Mining Techniques - Past and Present

**Chapter 1**

**Abstract**

Open Pit Mining

*Hani M. Alnawafleh*

ing, and artisan mining.

mountainous mining, and artisan mining.

**3**

production cycle

**1. Introduction**

*Awwad H. Altiti, Rami O. Alrawashdeh and*

Open pit mining method is one of the surface mining methods that has a traditional cone-shaped excavation and is usually employed to exploit a nearsurface, nonselective and low-grade zones deposits. It often results in high productivity and requires large capital investments, low operating costs, and good safety conditions. The main topics that will be discussed in this chapter will include an introduction into the general features of open pit mining, ore body characteristics and configurations, stripping ratios and stripping overburden methods, mine elements and parameters, open pit operation cycle, pit slope angle, stability of mine slopes, types of highwall failures, mine closure and reclamation, and different variants of surface mining methods including opencast mining, mountainous min-

**Keywords:** open pit mine, slope stability, mine reclamation, stripping ratio,

Open pit mining is defined as the method of extracting any near surface ore deposit using one or more horizontal benches to extract the ore while dumping overburden and tailings (waste) at a specified disposal site outside the final pit boundary. Open pit mining is used for the extraction of both metallic and nonmetallic ores. Open pit mining is considered different from quarrying in the sense that it selectively extracts ore rather than an aggregate or a dimensional stone product. Open pit mining is applied to disseminated ore bodies or steeply dipping veins or seams where the mining advance is toward increasing depths. Backfilling usually occurs until the pit is completed; even then, the high cost of filling these pits with all of the waste removed at the end of the mine life would seriously risk the project's economics. Few large open pits in the world could support such a costly obstacle. Open pit method is usually nonselective, and it includes all high and low-grade zones; whereas mining rate is nearly over 20,000 tons mined per day and often necessitates a large capital investment but generally results in high productivity, low operating cost, and good safety conditions [1]. The main purpose of this chapter is to discuss the general features of open pit mining, ore body characteristics and configurations, stripping ratios and stripping overburden methods, mine elements and parameters, open pit operation cycle, pit slope angle, stability of mine slopes, types of highwall failures, mine closure, and reclamation. The chapter will also discuss different variants of surface mining methods including opencast mining,

#### **Chapter 1**

## Open Pit Mining

*Awwad H. Altiti, Rami O. Alrawashdeh and Hani M. Alnawafleh*

#### **Abstract**

Open pit mining method is one of the surface mining methods that has a traditional cone-shaped excavation and is usually employed to exploit a nearsurface, nonselective and low-grade zones deposits. It often results in high productivity and requires large capital investments, low operating costs, and good safety conditions. The main topics that will be discussed in this chapter will include an introduction into the general features of open pit mining, ore body characteristics and configurations, stripping ratios and stripping overburden methods, mine elements and parameters, open pit operation cycle, pit slope angle, stability of mine slopes, types of highwall failures, mine closure and reclamation, and different variants of surface mining methods including opencast mining, mountainous mining, and artisan mining.

**Keywords:** open pit mine, slope stability, mine reclamation, stripping ratio, production cycle

#### **1. Introduction**

Open pit mining is defined as the method of extracting any near surface ore deposit using one or more horizontal benches to extract the ore while dumping overburden and tailings (waste) at a specified disposal site outside the final pit boundary. Open pit mining is used for the extraction of both metallic and nonmetallic ores. Open pit mining is considered different from quarrying in the sense that it selectively extracts ore rather than an aggregate or a dimensional stone product.

Open pit mining is applied to disseminated ore bodies or steeply dipping veins or seams where the mining advance is toward increasing depths. Backfilling usually occurs until the pit is completed; even then, the high cost of filling these pits with all of the waste removed at the end of the mine life would seriously risk the project's economics. Few large open pits in the world could support such a costly obstacle. Open pit method is usually nonselective, and it includes all high and low-grade zones; whereas mining rate is nearly over 20,000 tons mined per day and often necessitates a large capital investment but generally results in high productivity, low operating cost, and good safety conditions [1]. The main purpose of this chapter is to discuss the general features of open pit mining, ore body characteristics and configurations, stripping ratios and stripping overburden methods, mine elements and parameters, open pit operation cycle, pit slope angle, stability of mine slopes, types of highwall failures, mine closure, and reclamation. The chapter will also discuss different variants of surface mining methods including opencast mining, mountainous mining, and artisan mining.

#### **1.1 Features, technical and economic indicators of open pit development**

Compared to underground mining methods, the open pit mining method requires removing significant amount of overburden from the pit and moving it outside the mine. The cost of extraction of the ore from open pit constitutes the bulk of the total cost of mining operations, because the access to the ore body is so fast and requires less time compared to underground mining, i.e., extracting the ore below overburden can only begin with some lag time from the start of removing overburden. Also, open pit has virtually an unlimited ability to create and use highperformance large-sized mining and transportation equipment that can provide the highest technical and economic parameters. Open pit mining has higher productivity (3–5 times of underground methods), lower production costs, more safe and hygienic working conditions, more complete recovery of a mineral, and lower per unit production cost.

Open pit mining is characterized not only by its high share of total minerals production, but it is also considered as one of the surface mining methods that contributes to the construction of powerful performance quarries (100–150 million tons of rock a year reaching to a depth of 500 m). Capital cost of such huge open pits/quarries is very high, and the total cost for excavation of rock in the long term reaches hundreds of millions of dollars or more. Therefore, decisions on the construction of new or existing quarries should be economically justified. **Table 1** shows the advantages and disadvantages of open pit mining method [2, 3].

#### **1.2 Ore body characteristics and configurations**

Open pit mining is widely used with metallic ore bodies (aluminum, bauxite, copper, iron), and nearly all nonmetallic (coal, uranium, phosphate, etc.). It is a traditional cone-shaped excavation (although it can be of any shape, depending on the size and shape of the ore body) that is used when the ore body is typically pipeshaped, vein-type, and steeply dipping stratified or irregular [4]. The major open pit and ore body configurations are classified into the following:


removed to expose the ore for mining which generally results in a lower operating

In order to specify the maximum allowable stripping ratio (SRmax) of a surface mine, break even ratio can help to establishes the pit limits. SR max defined as the ratio of overburden to ore at the ultimate boundary of the pit, where the profit

SRmax ¼ ð Þ Value of ore � Production cost *=*Stripping cost (1)

cost [5]. The major types of stripping ratios are overall, instantaneous, and

**Advantages Disadvantages**

Limited by depth �500 m; technological limit imposed by equipment; and deposit beyond pit limits must be mined underground or left in place

Surface damaged may require reclamation; a bond

Requires large deposit to realize lowest cost, unless

Slope stability must be maintained; proper design and maintenance of benches plus good drainage

Requires provision of large waste disposal/dump

has to be added to the production cost

Weather can be detrimental; it can impede

Limited by stripping ratio

Lowest cost along with open cast mining High capital investment associated with large

equipment

very high grade

operations.

are essential

area

High productivity, i.e., highly mechanized and labor conserving (around 100–400 tons per employee-shift including both ore and waste)

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

High production rate (essentially unlimited, although small surface mines also possible)

Early production, development can be programmed to permit early start-up

key operators (e.g., drill, shovel)

changes

*Open Pit Mining*

productivity

may be considerable

underground hazards

*Flat lying seam or bed, flat terrain.*

**Table 1.**

Low labor requirement; can be unskilled except

Relatively flexible; can vary output if demand

Suitable for large equipment; permit high

Fairly low rock-breakage cost (drilling and blasting); superior to underground mining where

bench faces are less easily maintained

Simple development and access; minimal openings required although advanced stripping

Little if any bank support required; proper design and maintenance of benches can provide stability Good recovery; good health and safety; no

*Advantages and disadvantages of open pit mining method [2, 3].*

break-even.

**Figure 1.**

or,

**5**

margin is zero. It can be calculated as:

#### **1.3 Stripping ratio**

The parameter known as the *stripping ratio* represents the amount of uneconomic material that must be removed to uncover one unit of ore, i.e., the ratio of the number of tons of waste material removed to the number of tons of ore removed. Also, the ratio of the total volume of waste to the total volume of ore is defined as the *overall stripping ratio.* A lower stripping ratio means that less waste has to be


#### **Table 1.**

**1.1 Features, technical and economic indicators of open pit development**

unit production cost.

*Mining Techniques - Past, Present and Future*

**Figure 1**.

**Figure 2**.

**Figure 5**.

**1.3 Stripping ratio**

**4**

**1.2 Ore body characteristics and configurations**

pit and ore body configurations are classified into the following:

Compared to underground mining methods, the open pit mining method requires removing significant amount of overburden from the pit and moving it outside the mine. The cost of extraction of the ore from open pit constitutes the bulk of the total cost of mining operations, because the access to the ore body is so fast and requires less time compared to underground mining, i.e., extracting the ore below overburden can only begin with some lag time from the start of removing overburden. Also, open pit has virtually an unlimited ability to create and use highperformance large-sized mining and transportation equipment that can provide the highest technical and economic parameters. Open pit mining has higher productivity (3–5 times of underground methods), lower production costs, more safe and hygienic working conditions, more complete recovery of a mineral, and lower per

Open pit mining is characterized not only by its high share of total minerals production, but it is also considered as one of the surface mining methods that contributes to the construction of powerful performance quarries (100–150 million tons of rock a year reaching to a depth of 500 m). Capital cost of such huge open pits/quarries is very high, and the total cost for excavation of rock in the long term reaches hundreds of millions of dollars or more. Therefore, decisions on the construction of new or existing quarries should be economically justified. **Table 1** shows the advantages and disadvantages of open pit mining method [2, 3].

Open pit mining is widely used with metallic ore bodies (aluminum, bauxite, copper, iron), and nearly all nonmetallic (coal, uranium, phosphate, etc.). It is a traditional cone-shaped excavation (although it can be of any shape, depending on the size and shape of the ore body) that is used when the ore body is typically pipeshaped, vein-type, and steeply dipping stratified or irregular [4]. The major open

• Flat lying seam or bed, flat terrain (e.g., platinum reefs, coal), as shown in

• Massive deposit, flat terrain (e.g., iron-ore or sulfide deposits), as shown in

• Dipping seam or bed, flat terrain (e.g., anthracite), as shown in **Figure 3**.

• Massive deposit, high relief (e.g., copper sulfide), as shown in **Figure 4**.

• Thick-bedded deposits, little overburden (e.g., iron ore, coal) as shown in

The parameter known as the *stripping ratio* represents the amount of uneconomic material that must be removed to uncover one unit of ore, i.e., the ratio of the number of tons of waste material removed to the number of tons of ore removed. Also, the ratio of the total volume of waste to the total volume of ore is defined as the *overall stripping ratio.* A lower stripping ratio means that less waste has to be

*Advantages and disadvantages of open pit mining method [2, 3].*

**Figure 1.** *Flat lying seam or bed, flat terrain.*

removed to expose the ore for mining which generally results in a lower operating cost [5]. The major types of stripping ratios are overall, instantaneous, and break-even.

In order to specify the maximum allowable stripping ratio (SRmax) of a surface mine, break even ratio can help to establishes the pit limits. SR max defined as the ratio of overburden to ore at the ultimate boundary of the pit, where the profit margin is zero. It can be calculated as:

$$\text{SR}\_{\text{max}} = (\text{Value of ore} - \text{Production cost}) / \text{Stripping cost} \tag{1}$$

or,

SRmax <sup>¼</sup> Stripping allowance \$ð Þ *<sup>=</sup>*ton *<sup>=</sup>*Stripping cost m3

body beyond this maximum stripping ratio will have to be left or mined

• *Weight stripping ratio* = (27 � 1.7)/(2.5 � 1.36) = 13.5 tons of overburden per ton ore

SRmax � 2.5 m<sup>3</sup>

*Open Pit Mining*

underground.

*Example 1:*

density of 1.7 t/m<sup>3</sup>

*Solution:*

*Example 2:*

*Solution:*

waste for each ton ore.

**Figure 6.**

**7**

/ton (3.0 yd<sup>3</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

\$1.25, and \$1.50 per kg of refined metal at the smelter.

*Profit* = value of ore � production costs � stripping cost *Profit* = (7.04 � \$1.5) � \$5.9 � (15.53 � \$0.3) = 0

. Calculate the stripping ratios?

• *Volumetric stripping ratio* = 27/2.5 =10.8 m<sup>3</sup> of overburden per m<sup>3</sup> ore

• *Stripping ratio* = 27/(2.5 � 1.36) = 7.9 m3 of overburden per ton ore

*SRMax* = Value of ore � Production/Stripping cost per ton overburden *Recoverable copper per ton ore* = 0.8% � 88% � 1000 = 7.04 kg *At \$1.00/kg SRmax* = (7.04 � 5.90)/0.3 = 3.8 tons waste per ton ore *At \$1.25/kg SRmax* = (7.04 � 1.25) � 5.90/0.3 = 9.7 tons waste per ton ore *At \$1.50/kg SRmax* = (7.04 � 1.50) � 5.90/0.3 = 15.53 tons waste per ton ore

*A copper pit designed in this manner with varying ore grades and critical SRmax.*

The maximum allowable stripping ratio enables us to locate the ultimate pit boundary or limit based on prevailing economic, physical, and geometric conditions in the pit. A copper pit designed in this manner with varying ore grades and critical

A seam of coal has a density of 1.36 t/m3 and is 2.5 m thick. It is covered by 27 m of shale which has a

The head assay of a copper ore is 0.8% Cu. The expected overall copper recovery from the ore is 88%. Calculate the maximum stripping ratio if the total cost of production (excluding overburden removal) is \$5.90 per ton of ore and overburden removal costs are \$0.3 per ton of waste. Assume copper values of \$1.00,

To check that maximum stripping ratio has been reached; for \$1.50, it is possible to strip 15.53 tons

/ton) is shown in **Figure 6**. Ore occurring in the ore

*=*ton (2)

**Figure 2.** *Massive deposit, flat terrain.*

**Figure 3.** *Dipping seam or bed, flat terrain.*

**Figure 4.** *Massive deposit, high relief.*

**Figure 5.** *Thick-bedded deposits.*

*Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

> SRmax <sup>¼</sup> Stripping allowance \$ð Þ *<sup>=</sup>*ton *<sup>=</sup>*Stripping cost m3 *=*ton (2)

The maximum allowable stripping ratio enables us to locate the ultimate pit boundary or limit based on prevailing economic, physical, and geometric conditions in the pit. A copper pit designed in this manner with varying ore grades and critical SRmax � 2.5 m<sup>3</sup> /ton (3.0 yd<sup>3</sup> /ton) is shown in **Figure 6**. Ore occurring in the ore body beyond this maximum stripping ratio will have to be left or mined underground.

#### *Example 1:*

**Figure 2.**

**Figure 3.**

**Figure 4.**

**Figure 5.**

**6**

*Thick-bedded deposits.*

*Massive deposit, high relief.*

*Massive deposit, flat terrain.*

*Mining Techniques - Past, Present and Future*

*Dipping seam or bed, flat terrain.*

A seam of coal has a density of 1.36 t/m3 and is 2.5 m thick. It is covered by 27 m of shale which has a density of 1.7 t/m<sup>3</sup> . Calculate the stripping ratios? *Solution:*


#### *Example 2:*

The head assay of a copper ore is 0.8% Cu. The expected overall copper recovery from the ore is 88%. Calculate the maximum stripping ratio if the total cost of production (excluding overburden removal) is \$5.90 per ton of ore and overburden removal costs are \$0.3 per ton of waste. Assume copper values of \$1.00, \$1.25, and \$1.50 per kg of refined metal at the smelter.

*Solution:*

*SRMax* = Value of ore � Production/Stripping cost per ton overburden *Recoverable copper per ton ore* = 0.8% � 88% � 1000 = 7.04 kg *At \$1.00/kg SRmax* = (7.04 � 5.90)/0.3 = 3.8 tons waste per ton ore *At \$1.25/kg SRmax* = (7.04 � 1.25) � 5.90/0.3 = 9.7 tons waste per ton ore *At \$1.50/kg SRmax* = (7.04 � 1.50) � 5.90/0.3 = 15.53 tons waste per ton ore To check that maximum stripping ratio has been reached; for \$1.50, it is possible to strip 15.53 tons waste for each ton ore.

*Profit* = value of ore � production costs � stripping cost *Profit* = (7.04 � \$1.5) � \$5.9 � (15.53 � \$0.3) = 0

**Figure 6.** *A copper pit designed in this manner with varying ore grades and critical SRmax.*

#### **1.4 Stripping overburden methods**

Overburden is a waste rock material that must be removed to expose the underlying ore body. It is preferred to extract as little overburden as possible in order to access the ore of interest, but a larger volume of waste rock is removed when the mineral deposit is deep. Most removal operations (which includes drilling, loading, blasting, and haulage) are cyclical. This is true for hard rock overburden which must be drilled and blasted first. An exception to the cyclical effect is dredging method used in hydraulic surface mining and some types of loose material mining (soil) with bucket wheel excavators. The percentage of waste rock to ore excavated is defined as the stripping ratio. Stripping ratios of 2:1 up to 4:1 are common in large mining operations. Ratios above 6:1 tend to be less economically feasible depending on the type of ore extracted. Once removed, overburden can be used for road and tailings' construction or may have a non-mining commercial value as a backfilling material. In selecting a particular stripping method and its corresponding equipment, the ultimate aim is the removal of material (waste and burden) at the least possible cost [6]. Stripping methods are classified into:


#### *1.4.1 Declining stripping method*

In this method, each bench of ore has to be mined in sequence, and the waste in the particular bench has to be removed to the pit limit. The ore is easily accessible in the subsequent benches and the operating working space is widely available. Furthermore, all equipment usually work in the same level and so no contamination from waste blasting is left above the ore body. This method is highly productive especially at the beginning where equipment required is at minimal toward the end of the mine life. The primary disadvantage of this method is that the overall operating costs are at maximum during the initial years of operation when the maximum repayment of capital is needed and so cashflows are required to handle interest and repayment of capital (see **Figure 7**).

advantage of removing the extreme conditions of the former two stripping methods outlined. Equipment fleet size and labor requirements throughout the project life are relatively constant. In this method, a good profit can be generated initially to increase cash flows. The labor and equipment fleet can be increased to maximum capacity over a period of time, and then, they can decrease gradually toward the end of the mine life. Distinct mining and stripping areas can be operated

Open pit mines are constructed of series of benches that are bisected by mine access and haulage roads angling down from the rim of the pit to the bottom. The bench height is the vertical distance between each horizontal level of the pit. The elements of a bench are illustrated in **Figures 10** and **11**, unless geological conditions dictate, otherwise all benches should have the same height. The bench height should be designed as high as possible within the limits of the size and type of the machine or equipment selected for the required production. The bench should not be so high

simultaneously, allowing flexibility in planning (see **Figure 9**).

**1.5 Mine elements and parameters**

**Figure 8.**

**9**

**Figure 7.**

*Open Pit Mining*

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

*Declining stripping method.*

*Increasing stripping method.*

#### *1.4.2 Increasing stripping method*

In this method, stripping of overburden is performed as needed to uncover the ore. The working slopes of the waste faces are essentially maintained parallel to the overall pit slope angle. This method also allows for maximum profit in the initial years of operation and greatly reduces the investment risk in waste removal for ore to be mined at a future date. It is considered as a very popular method whereas mining economics or cutoff stripping ratio is likely to change in a very short time. This method is sometimes impractical because of its small spaces (narrow benches). It is available for operating a large number of equipment especially at the beginning of stripping (see **Figure 8**).

#### *1.4.3 Constant stripping method*

This method aims to remove the waste at a rate estimated by the overall stripping ratio. The working slope of the waste faces starts very shallow, but increases as mining depth increases until it equals the overall pit slope. This method has the

*Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

**1.4 Stripping overburden methods**

*Mining Techniques - Past, Present and Future*

a. declining;

c. constant.

b. Increasing; and

*1.4.1 Declining stripping method*

repayment of capital (see **Figure 7**).

*1.4.2 Increasing stripping method*

*1.4.3 Constant stripping method*

**8**

possible cost [6]. Stripping methods are classified into:

Overburden is a waste rock material that must be removed to expose the underlying ore body. It is preferred to extract as little overburden as possible in order to access the ore of interest, but a larger volume of waste rock is removed when the mineral deposit is deep. Most removal operations (which includes drilling, loading, blasting, and haulage) are cyclical. This is true for hard rock overburden which must be drilled and blasted first. An exception to the cyclical effect is dredging method used in hydraulic surface mining and some types of loose material mining (soil) with bucket wheel excavators. The percentage of waste rock to ore excavated is defined as the stripping ratio. Stripping ratios of 2:1 up to 4:1 are common in large mining operations. Ratios above 6:1 tend to be less economically feasible depending on the type of ore extracted. Once removed, overburden can be used for road and tailings' construction or may have a non-mining commercial value as a backfilling material. In selecting a particular stripping method and its corresponding equipment, the ultimate aim is the removal of material (waste and burden) at the least

In this method, each bench of ore has to be mined in sequence, and the waste in the particular bench has to be removed to the pit limit. The ore is easily accessible in the subsequent benches and the operating working space is widely available. Furthermore, all equipment usually work in the same level and so no contamination from waste blasting is left above the ore body. This method is highly productive especially at the beginning where equipment required is at minimal toward the end of the mine life. The primary disadvantage of this method is that the overall operating costs are at maximum during the initial years of operation when the maximum repayment of capital is needed and so cashflows are required to handle interest and

In this method, stripping of overburden is performed as needed to uncover the ore. The working slopes of the waste faces are essentially maintained parallel to the overall pit slope angle. This method also allows for maximum profit in the initial years of operation and greatly reduces the investment risk in waste removal for ore to be mined at a future date. It is considered as a very popular method whereas mining economics or cutoff stripping ratio is likely to change in a very short time. This method is sometimes impractical because of its small spaces (narrow benches). It is available for operating a large number of equipment especially at the beginning of stripping (see **Figure 8**).

This method aims to remove the waste at a rate estimated by the overall stripping ratio. The working slope of the waste faces starts very shallow, but increases as mining depth increases until it equals the overall pit slope. This method has the

**Figure 8.** *Increasing stripping method.*

advantage of removing the extreme conditions of the former two stripping methods outlined. Equipment fleet size and labor requirements throughout the project life are relatively constant. In this method, a good profit can be generated initially to increase cash flows. The labor and equipment fleet can be increased to maximum capacity over a period of time, and then, they can decrease gradually toward the end of the mine life. Distinct mining and stripping areas can be operated simultaneously, allowing flexibility in planning (see **Figure 9**).

#### **1.5 Mine elements and parameters**

Open pit mines are constructed of series of benches that are bisected by mine access and haulage roads angling down from the rim of the pit to the bottom. The bench height is the vertical distance between each horizontal level of the pit. The elements of a bench are illustrated in **Figures 10** and **11**, unless geological conditions dictate, otherwise all benches should have the same height. The bench height should be designed as high as possible within the limits of the size and type of the machine or equipment selected for the required production. The bench should not be so high

#### **Figure 9.** *Constant stripping method.*

of ore a day to large companies operated by governmental and private corporations that extract more than one million tons of material a day. The largest mining operations can involve many square kilometers in area. The production cycle also referred to as the mine unit operation that consists of ripping and dozing, drilling,

Typically, bulldozer, wheel dozers, and motor graders are the most common equipment used, in which material transport distance is short and it can be pushed by a blade. The dozer has a large blade capacity and it is designed specifically for bulk material excavation, whereas the motor grader is a machine with a long blade used to create a flat surface during the grading process. These machines cannot "lift" the material, i.e., they do not have a load elevation capacity (**Figure 12**).

The ore deposit can be mined by means of drilling and blasting in order to fracture the rock into a loadable size. Blasting parameters should be matched with mechanical machines for drilling of blast holes and charging of explosives. Blast holes are drilled in well-defined patterns, which consist of several parallel rows. In bench blasting, the normal blast hole patterns are square, rectangular, and staggered, **Figure 13**. The most effective pattern is the staggered pattern, which gives

the optimum distribution of the explosive energy in the rock.

blasting, loading, and hauling (see **Figure 12**).

**2.1 Ripping and dozing**

*Detailed mining operation in an open pit.*

**Figure 11.**

*Open Pit Mining*

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

**2.2 Drilling and blasting**

**11**

**Figure 10.** *Main mine elements and parameters.*

that it will cause safety problems. The bench height in open pit mines will usually range from 15 m in large mines (e.g., copper) to as little as 1 m in small mines (e.g., uranium) [7]. The slope angle of the pit walls is a critical factor. If the slope angle is too steep, the pit walls may collapse. If it is too shallow, excessive waste rock may need to be removed. The pit wall has to remain stable as long as mining activity continues. The stability of the pit walls should be examined as carefully as possible. For example, rock strength, faults, joints, and fractures are key factors in the evaluation of the proper slope angle.

#### **2. Open pit mine operations**

The main economic goal in open pit mining is to remove the smallest amount of material while obtaining the greatest return on investment by processing the most marketable mineral product. The higher the grade of the ore, the greater the value received. To reduce the capital investment, an operation plan has to be developed in order to precisely dictate the way in which the ore body has to be extracted. Open pit mines vary in scale from small private enterprises processing a few hundred tons

#### **Figure 11.** *Detailed mining operation in an open pit.*

of ore a day to large companies operated by governmental and private corporations that extract more than one million tons of material a day. The largest mining operations can involve many square kilometers in area. The production cycle also referred to as the mine unit operation that consists of ripping and dozing, drilling, blasting, loading, and hauling (see **Figure 12**).

#### **2.1 Ripping and dozing**

Typically, bulldozer, wheel dozers, and motor graders are the most common equipment used, in which material transport distance is short and it can be pushed by a blade. The dozer has a large blade capacity and it is designed specifically for bulk material excavation, whereas the motor grader is a machine with a long blade used to create a flat surface during the grading process. These machines cannot "lift" the material, i.e., they do not have a load elevation capacity (**Figure 12**).

#### **2.2 Drilling and blasting**

The ore deposit can be mined by means of drilling and blasting in order to fracture the rock into a loadable size. Blasting parameters should be matched with mechanical machines for drilling of blast holes and charging of explosives. Blast holes are drilled in well-defined patterns, which consist of several parallel rows. In bench blasting, the normal blast hole patterns are square, rectangular, and staggered, **Figure 13**. The most effective pattern is the staggered pattern, which gives the optimum distribution of the explosive energy in the rock.

that it will cause safety problems. The bench height in open pit mines will usually range from 15 m in large mines (e.g., copper) to as little as 1 m in small mines (e.g., uranium) [7]. The slope angle of the pit walls is a critical factor. If the slope angle is too steep, the pit walls may collapse. If it is too shallow, excessive waste rock may need to be removed. The pit wall has to remain stable as long as mining activity continues. The stability of the pit walls should be examined as carefully as possible. For example, rock strength, faults, joints, and fractures are key factors in the

The main economic goal in open pit mining is to remove the smallest amount of material while obtaining the greatest return on investment by processing the most marketable mineral product. The higher the grade of the ore, the greater the value received. To reduce the capital investment, an operation plan has to be developed in order to precisely dictate the way in which the ore body has to be extracted. Open pit mines vary in scale from small private enterprises processing a few hundred tons

evaluation of the proper slope angle.

**2. Open pit mine operations**

*Main mine elements and parameters.*

**Figure 9.**

**Figure 10.**

**10**

*Constant stripping method.*

*Mining Techniques - Past, Present and Future*

trucks that can be loaded in 3–5 cycles of the shovel. Many factors determine the preference of loading equipment. For example, with a hard digging rock, tracked shovels are more advisable. On the other hand, rubber-tyred loaders have lower capital cost and are better for loading materials that are low in volume and easy to dig. Furthermore, loaders are very mobile and well applicable for mining scenarios requiring rapid movements from one area to another. Loaders are also often used to load, haul, and dump material into crushers from blending stock piles placed near

Hydraulic shovels and cable shovels are common equipment used in open pit mining. Hydraulic shovels (**Figure 15**) are not chosen for digging hard rock, and cable shovels are generally available in larger sizes. Large cable shovels (**Figure 16**) with payloads of about 50 cubic meters and greater are used at mines where production exceeds 200,000 tons per day, whereas hydraulic shovels are more

crushers by haul trucks, **Figure 14**.

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

*Open Pit Mining*

**Figure 14.**

**Figure 15.** *Hydraulic shovels.*

**Figure 16.** *Cable or rope shovels.*

**13**

*Loading material using front end loader.*

**Figure 12.** *Open pit operations cycle.*

#### **2.3 Loading and hauling**

Nowadays, surface mining is conducted using shovels, front end loaders or hydraulic shovels. In open pit mining, loading equipment is matched with haul

#### *Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

trucks that can be loaded in 3–5 cycles of the shovel. Many factors determine the preference of loading equipment. For example, with a hard digging rock, tracked shovels are more advisable. On the other hand, rubber-tyred loaders have lower capital cost and are better for loading materials that are low in volume and easy to dig. Furthermore, loaders are very mobile and well applicable for mining scenarios requiring rapid movements from one area to another. Loaders are also often used to load, haul, and dump material into crushers from blending stock piles placed near crushers by haul trucks, **Figure 14**.

Hydraulic shovels and cable shovels are common equipment used in open pit mining. Hydraulic shovels (**Figure 15**) are not chosen for digging hard rock, and cable shovels are generally available in larger sizes. Large cable shovels (**Figure 16**) with payloads of about 50 cubic meters and greater are used at mines where production exceeds 200,000 tons per day, whereas hydraulic shovels are more

**Figure 14.** *Loading material using front end loader.*

**Figure 15.** *Hydraulic shovels.*

**Figure 16.** *Cable or rope shovels.*

**2.3 Loading and hauling**

*Blast holes drilling patterns.*

**Figure 13.**

**12**

**Figure 12.**

*Open pit operations cycle.*

*Mining Techniques - Past, Present and Future*

Nowadays, surface mining is conducted using shovels, front end loaders or hydraulic shovels. In open pit mining, loading equipment is matched with haul flexible on the mine face and they enable greater operator control to selectively load from both directions (top and bottom of the mine face).

The importance of haul trucks in the history of surface mining cannot be overstated. Hand labor, wheelbarrows, horse-drawn vehicles, and ore cars were the principal means of earth-moving equipment until the early twentieth century. The advent of the internal combustion engine led to the development of the haul truck in the mining industry. Open pit mining requires a great demand for truck transport of ore and waste rock. The efficiency and greater load capacity of electrical and diesel-powered haul trucks became the preferred method for hauling in surface mining, gradually replacing rail haulage by the 1960s. Today, the average cost of a new haul truck is \$3.5 million [8]. Most trucks have capacities ranging from less than 50 tons per load to 363 tons per load in large trucks such as Caterpillars 797 series load truck. Some mining companies choose to replace trucks with conveyor belt systems. For example, the Brazilian mining company "Vale" has recently replaced its mine trucks with 23 miles of conveyor belts at its iron ore mine, linking the ore deposits to the company's processing plant [9, 10].

#### **3. Pit slope angle and stability**

Slope angle is required during the early feasibility study. The degree of confidence on calculating slope angle depends upon the condition applicable. The major pit slope angle conditions can be divided into:

mechanisms will enable us to identify potential problems before they become actual problems and to limit exposure to dangerous conditions. The most common types of failure include plane failure, wedge failure, toppling failure, and circular failure. Except for the circular failure, these usually occur along preexisting discontinuities.

This slide in **Figure 18** illustrates a typical plane failure of a highwall. Notice that the rockslide occurs along this discontinuity which daylights on the highwall and dips toward the pit. If this sliding plane does not daylight, or dips away from the pit, the slope is stable. Even if the joint daylights, in order for the slide to occur, the weight of this sliding block must exceed the frictional resistance along the discontinuity. **Figure 19** shows an example of a slope, which is plagued by large planar failures, and leads to a slide off rocks along natural, parallel, and bedding planes.

A wedge failure occurs when two discontinuities meet and their intersecting line daylights on the slope face and dips toward the pit. If these conditions do not occur,

Example of each are the following:

*3.1.1 Planar failure*

*Mine slope geomechanics.*

*Open Pit Mining*

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

**Figure 17.**

*3.1.2 Wedge failure*

**Figure 18.** *Planar failure.*

**15**


During the pre-production period, the operating slopes should, however, be as steep as possible. The working slope can then be flattened until they reach the outer surface intercepts. The horizontal flow of stress through a vertical section both with and without the presence of the final pit is shown in **Figure 17**.

With the excavation of the pit, the preexisting horizontal stresses are forced to flow beneath the pit bottom. The vertical stresses are also reduced due to the removal of the rock. The rock lying between the pit outline is largely distressed. As a result of stress removal, cracks and joints can open. Cohesive and friction forces restraining the rock in place are reduced. Groundwater can more easily flow reducing the effective normal force on potential failure planes. With increasing pit depth, the extent of the stressed zone increase and the failure becomes more severe.

#### **3.1 Types of highwall failures**

There are several mechanisms by which highwall instability can occur. While we cannot expect to prevent all highwall failures, a better understanding of these

**Figure 17.** *Mine slope geomechanics.*

flexible on the mine face and they enable greater operator control to selectively load

Slope angle is required during the early feasibility study. The degree of confidence on calculating slope angle depends upon the condition applicable. The major

a. mining a shallow high-grade ore body in favorable geological and climatic conditions. Slope angles are unimportant economically and flat slopes can be

conditions. Slope angles are important but not critical in determining economics of mining. Approximate analysis of slope stability is normally adequate; and

conditions. Slope angles are critical in terms of both economics of mining and safely of operation. Detailed geological and groundwater studies followed by

During the pre-production period, the operating slopes should, however, be as steep as possible. The working slope can then be flattened until they reach the outer surface intercepts. The horizontal flow of stress through a vertical section both with

With the excavation of the pit, the preexisting horizontal stresses are forced to

There are several mechanisms by which highwall instability can occur. While we

cannot expect to prevent all highwall failures, a better understanding of these

flow beneath the pit bottom. The vertical stresses are also reduced due to the removal of the rock. The rock lying between the pit outline is largely distressed. As a result of stress removal, cracks and joints can open. Cohesive and friction forces restraining the rock in place are reduced. Groundwater can more easily flow reducing the effective normal force on potential failure planes. With increasing pit depth, the extent of the stressed zone increase and the failure becomes more severe.

b. mining a variable grade ore body in reasonable geological and climatic

c. mining a low-grade ore body in unfavorable geological and climatic

The importance of haul trucks in the history of surface mining cannot be overstated. Hand labor, wheelbarrows, horse-drawn vehicles, and ore cars were the principal means of earth-moving equipment until the early twentieth century. The advent of the internal combustion engine led to the development of the haul truck in the mining industry. Open pit mining requires a great demand for truck transport of ore and waste rock. The efficiency and greater load capacity of electrical and diesel-powered haul trucks became the preferred method for hauling in surface mining, gradually replacing rail haulage by the 1960s. Today, the average cost of a new haul truck is \$3.5 million [8]. Most trucks have capacities ranging from less than 50 tons per load to 363 tons per load in large trucks such as Caterpillars 797 series load truck. Some mining companies choose to replace trucks with conveyor belt systems. For example, the Brazilian mining company "Vale" has recently replaced its mine trucks with 23 miles of conveyor belts at its iron ore mine, linking

from both directions (top and bottom of the mine face).

*Mining Techniques - Past, Present and Future*

the ore deposits to the company's processing plant [9, 10].

used. No consideration of slope stability is required;

comprehensive stability analysis are usually required.

and without the presence of the final pit is shown in **Figure 17**.

**3. Pit slope angle and stability**

**3.1 Types of highwall failures**

**14**

pit slope angle conditions can be divided into:

mechanisms will enable us to identify potential problems before they become actual problems and to limit exposure to dangerous conditions. The most common types of failure include plane failure, wedge failure, toppling failure, and circular failure. Except for the circular failure, these usually occur along preexisting discontinuities. Example of each are the following:

#### *3.1.1 Planar failure*

This slide in **Figure 18** illustrates a typical plane failure of a highwall. Notice that the rockslide occurs along this discontinuity which daylights on the highwall and dips toward the pit. If this sliding plane does not daylight, or dips away from the pit, the slope is stable. Even if the joint daylights, in order for the slide to occur, the weight of this sliding block must exceed the frictional resistance along the discontinuity. **Figure 19** shows an example of a slope, which is plagued by large planar failures, and leads to a slide off rocks along natural, parallel, and bedding planes.

#### *3.1.2 Wedge failure*

A wedge failure occurs when two discontinuities meet and their intersecting line daylights on the slope face and dips toward the pit. If these conditions do not occur,

**Figure 18.** *Planar failure.*

**Figure 19.** *Large planar failure.*

you cannot have a wedge failure. The weight of the block also has to exceed the frictional resistance along the failure surface to have failure, **Figure 20**.

As shown in **Figure 21**, the failure can follow trends since joints tend to occur in repeating patterns. Note here the failure on the top bench, and on the next bench, should probably expect another at the next level down.

#### *3.1.3 Toppling failure*

Toppling failures look like **Figure 22**. A toppling failure can occur when the discontinuities dip very close to vertical but away from the pit. The discontinuities can be natural or they can be caused by the mining process.

If the mine progresses from left to right, there will be continuous problems, because of the way these cracks are oriented. On the other hand, if the mine goes from right to left, mine operators do not have to worry about toppling-type failure; so, decisions made during mine planning can have a profound effect on the stability

**Figure 20.** *Wedge failure.*

of the highwalls. **Figure 23** shows a picture of a toppling failure that resulted in a

In slopes excavated in soil or highly jointed and weathered rock mass where

(**Figures 24** and **25**) results from a process of localization of deformations. It is an arch type of landslides; however, the specific shape of this failure surface and the

there are no geological structures to control the failure, the most unstable failure surface is approximately a circular arc. This circular failure surface

associated failure mechanism cannot be generalized [11].

fatality to a blast hole drill operator.

*3.1.4 Circular failure*

*Circular failure mechanism.*

**Figure 23.**

**Figure 22.** *Toppling failure.*

*Open Pit Mining*

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

**Figure 24.**

**17**

*Toppling failure example.*

**Figure 21.** *Trend in wedge failure.*

*Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

**Figure 22.** *Toppling failure.*

you cannot have a wedge failure. The weight of the block also has to exceed the

As shown in **Figure 21**, the failure can follow trends since joints tend to occur in repeating patterns. Note here the failure on the top bench, and on the next bench,

Toppling failures look like **Figure 22**. A toppling failure can occur when the discontinuities dip very close to vertical but away from the pit. The discontinuities

If the mine progresses from left to right, there will be continuous problems, because of the way these cracks are oriented. On the other hand, if the mine goes from right to left, mine operators do not have to worry about toppling-type failure; so, decisions made during mine planning can have a profound effect on the stability

frictional resistance along the failure surface to have failure, **Figure 20**.

should probably expect another at the next level down.

*Mining Techniques - Past, Present and Future*

can be natural or they can be caused by the mining process.

*3.1.3 Toppling failure*

**Figure 19.** *Large planar failure.*

**Figure 20.** *Wedge failure.*

**Figure 21.**

**16**

*Trend in wedge failure.*

**Figure 24.** *Circular failure mechanism.*

of the highwalls. **Figure 23** shows a picture of a toppling failure that resulted in a fatality to a blast hole drill operator.

#### *3.1.4 Circular failure*

In slopes excavated in soil or highly jointed and weathered rock mass where there are no geological structures to control the failure, the most unstable failure surface is approximately a circular arc. This circular failure surface (**Figures 24** and **25**) results from a process of localization of deformations. It is an arch type of landslides; however, the specific shape of this failure surface and the associated failure mechanism cannot be generalized [11].

Land use plan at the end of mining has to be set in order to determine what the mine site will look like and how the lands will be used after the mine is closed and fully reclaimed. The mine must operate and close such that the land and water in and around the mine site are less disturbed and environmentally safe and sound like original. It is the responsibility of the mining company to pay for reclamation and closure costs. To ensure that funds are available for closure, the mining company will normally be required to post a financial security (a reclamation bond) before

"Progressive reclamation" is usually part of the overall closure plan. Progressive reclamation means that once a part of the mine site is no longer needed, it will be reclaimed rather than waiting for all aspects of operation to cease. For example, waste rock piles will be reclaimed as soon as they have reached their permitted size. The general rehabilitation goals require rehabilitation of areas disturbed by mining to result in sites that are safe to humans and wildlife, nonpolluting, stable, and able to sustain an agreed postmining land use. The process of reclamation

a. *Recontouring*: the ground is re-sloped and contoured to a profile that will be stable and that provides proper drainage, facilitates the growth of vegetation,

b. *Capping with a growth medium*: waste rock piles and other areas of the mine site will need to be covered with a soil material that is suitable for the growth

c. *Seeding and fertilizing*: this usually takes place over many years. Fast growing grasses may be planted in order to stabilize the soil followed by shrubs and

d. *Monitoring*: plants in areas that are to be used for grazing will be tested to ensure they contain acceptable levels of metals and other possible contaminants.

**5. Variants of surface mining methods: strip mining, mountainous**

Variants of open pit mining are limited to a number of other surface mining methods, which include strip mining, high wall mining, and quarrying. Strip (open cast) mining is used extensively for the surface mining of important commodities such as coal and phosphate ores. Casting is the process of excavation and dumping into a final location. This type of mining involves removing the overburden and extracting the valuable mineral deposit. Strip mining is applicable to shallow, flatlying deposits [15]. It is a method that is generally applied on a large scale with low mining costs and high productivity and that has minimum land degradation [16, 17]. In Jordan, strip is used for the extraction of oil shale and phosphate ores. These mines are located at the central and southern parts of the country (e.g.,

Strip mining differs from open pit in that the overburden is not transported to waste dumps but cast directly into adjacent mind-out panels, i.e., reclamation is contemporaneous with extraction. These mines often occupy a large area of land for ore excavation and overburden disposal. Strips are large rectangular parallel pits that extend to more than a mile in length [18]. After the removal of vegetation and topsoil, the mining begins with an initial rectangular box cut. The dragline is used

mining starts.

*Open Pit Mining*

of plants.

**Figure 27**).

**19**

normally involves the following steps [12–14]:

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

and provides various habitats for wildlife.

trees depending on the end use plan.

**mining, and artisan mining**

**Figure 25.** *Circular slope failure at the open pit of the Bingham Canyon Mine in Utah.*

### **4. Mine closure and reclamation**

In general, mining has a significant negative impact on environment. Due to its nature, it leads to severe degradation of the landscape. Many factors such as drainage, air, soil and water quality, noise levels, ground vibrations, human health, and habitation are mostly affected by mining activities. When the extraction of mine reserve is over, the distorted landscape has to be reclaimed in order to reduce the damaging effects of open pit mining and bring back the landscape and its surroundings, see **Figure 26**.

**Figure 26.** *Open pit mining before and after reclamation.*

#### *Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

Land use plan at the end of mining has to be set in order to determine what the mine site will look like and how the lands will be used after the mine is closed and fully reclaimed. The mine must operate and close such that the land and water in and around the mine site are less disturbed and environmentally safe and sound like original. It is the responsibility of the mining company to pay for reclamation and closure costs. To ensure that funds are available for closure, the mining company will normally be required to post a financial security (a reclamation bond) before mining starts.

"Progressive reclamation" is usually part of the overall closure plan. Progressive reclamation means that once a part of the mine site is no longer needed, it will be reclaimed rather than waiting for all aspects of operation to cease. For example, waste rock piles will be reclaimed as soon as they have reached their permitted size.

The general rehabilitation goals require rehabilitation of areas disturbed by mining to result in sites that are safe to humans and wildlife, nonpolluting, stable, and able to sustain an agreed postmining land use. The process of reclamation normally involves the following steps [12–14]:


#### **5. Variants of surface mining methods: strip mining, mountainous mining, and artisan mining**

Variants of open pit mining are limited to a number of other surface mining methods, which include strip mining, high wall mining, and quarrying. Strip (open cast) mining is used extensively for the surface mining of important commodities such as coal and phosphate ores. Casting is the process of excavation and dumping into a final location. This type of mining involves removing the overburden and extracting the valuable mineral deposit. Strip mining is applicable to shallow, flatlying deposits [15]. It is a method that is generally applied on a large scale with low mining costs and high productivity and that has minimum land degradation [16, 17]. In Jordan, strip is used for the extraction of oil shale and phosphate ores. These mines are located at the central and southern parts of the country (e.g., **Figure 27**).

Strip mining differs from open pit in that the overburden is not transported to waste dumps but cast directly into adjacent mind-out panels, i.e., reclamation is contemporaneous with extraction. These mines often occupy a large area of land for ore excavation and overburden disposal. Strips are large rectangular parallel pits that extend to more than a mile in length [18]. After the removal of vegetation and topsoil, the mining begins with an initial rectangular box cut. The dragline is used

**4. Mine closure and reclamation**

*Mining Techniques - Past, Present and Future*

*Circular slope failure at the open pit of the Bingham Canyon Mine in Utah.*

**Figure 25.**

**Figure 26.**

**18**

*Open pit mining before and after reclamation.*

surroundings, see **Figure 26**.

In general, mining has a significant negative impact on environment. Due to its nature, it leads to severe degradation of the landscape. Many factors such as drainage, air, soil and water quality, noise levels, ground vibrations, human health, and habitation are mostly affected by mining activities. When the extraction of mine reserve is over, the distorted landscape has to be reclaimed in order to reduce the

damaging effects of open pit mining and bring back the landscape and its

for overburden removal. As the overburden is removed from one portion of a mineral deposit, it is used to fill in the trench left by the previous removal [19]. The

**Figure 28** shows typical dragline operation. Stripping process continues along parallel strips. Where the deposit becomes thinner, or dipping more below the surface, or in the case of dramatic increase in the stripping ratio, the mining operation must be ceased [19]. Shovel-truck system is currently adapted for extracting phosphate ore in several phosphate mines in Jordan (**Figure 29**); especially in Al-Shidiyah, Al-Abiad, and Al-Hasa mines. Since shovel truck removal of

backfilled area is then replanted during the reclamation process.

**Figure 31.**

**21**

**Figure 30.**

*Open Pit Mining*

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

*Overburden removal at Attarat Oil shale mine, Jordan.*

*Dragline removes overburden at Al-Shidiyah phosphate mine, Jordan.*

**Figure 27.** *Oil shale extraction project at Attarat Oil Shale mine, Jordan.*

**Figure 28.** *Typical dragline operation [20].*

**Figure 29.** *During loading A1 phosphate layer at Al-Shidiyah phosphate mines.*

#### *Open Pit Mining DOI: http://dx.doi.org/10.5772/intechopen.92208*

for overburden removal. As the overburden is removed from one portion of a mineral deposit, it is used to fill in the trench left by the previous removal [19]. The backfilled area is then replanted during the reclamation process.

**Figure 28** shows typical dragline operation. Stripping process continues along parallel strips. Where the deposit becomes thinner, or dipping more below the surface, or in the case of dramatic increase in the stripping ratio, the mining operation must be ceased [19]. Shovel-truck system is currently adapted for extracting phosphate ore in several phosphate mines in Jordan (**Figure 29**); especially in Al-Shidiyah, Al-Abiad, and Al-Hasa mines. Since shovel truck removal of

**Figure 30.** *Dragline removes overburden at Al-Shidiyah phosphate mine, Jordan.*

**Figure 31.** *Overburden removal at Attarat Oil shale mine, Jordan.*

**Figure 27.**

**Figure 28.**

**Figure 29.**

**20**

*Typical dragline operation [20].*

*Oil shale extraction project at Attarat Oil Shale mine, Jordan.*

*Mining Techniques - Past, Present and Future*

*During loading A1 phosphate layer at Al-Shidiyah phosphate mines.*

overburden generally costs at least three times as much as dragline stripping, the dragline is currently implemented for removing overburden from phosphate ore in those mines (**Figure 30**). On the other hand, shovel truck removal of overburden is currently used in Attarat oil shale mine (**Figure 31**).

**References**

*Open Pit Mining*

p. 2161

Moscow; 1986. p. 312

techniques. Journal for the

[5] Introductory HH. Mining

2019;**29**(2):217-228

15 November 2019]

2019]

**23**

[1] Wetherelt A, Peter K, Wielen V. Introduction to open pit mining. In: SME Mining Engineering Handbook. 2nd ed. Colorado: Society for Mining, Metallurgy, and Exploration Inc; 2011.

*DOI: http://dx.doi.org/10.5772/intechopen.92208*

[10] McShane J. Metal Products Advances in Material Hauling for Mining Operations. 2020. Available from: https://www.mcshanemetalprod ucts.com/blog-post/advances-materia l-hauling-mining-operations/ [Accessed:

[11] Fleurisson J. Slope design and implementation in open pit mines: Geological and geomechanical

approach. Procedia Engineering. 2011;

[12] Stevens R. Mineral Exploration and Mining Essentials. British Colombia: Pakawau GeoManagement Inc./British Columbia Institute of Technology; 2014.

[13] Kuter N. Reclamation of Degraded Landscapes Due to Opencast Mining. Cankiri, Turkey: Department of Landscape Architecture, Faculty of Forestry, Cankiri Karatekin University;

2013. DOI: 10.5722/55796

[14] Liu H. Strategic Planning for Dragline Excavation Sequencing [PhD thesis]. Australia: The University of Queensland; 2018. Available from: https://espace.library.uq.edu.au/ [Accessed: 18 April 2020]

[15] Haldar S. Mineral Exploration: Principles and Applications. 2nd ed. Oxford: Elsevier; 2018. p. 378. ISBN:

Darling P, editor. SME Mining Engineering Handbook. Vol. 1. Colorado: SME; 2011. pp. 1031-1046

https://www.researchgate.net/ publication/301824314\_Mining\_ Methods\_Part\_I-Surface\_mining. [Accessed: 15 December 2019]

[16] Brown I. Strip mining. Ch. 10.11. In:

[17] Harraz H. Mining Methods: Part I-Surface Mining. 2010. Available from:

9780128140222

10 November 2019]

**46**:27-38

p. 317

[2] Tomakov P, Naumov I. Technology Mechanization and Organization of Surface Mining. 2nd ed. NEDRA:

[3] Bullivant D. Current surface mining

Transportation of Materials in Bulk: Bulk Solids Handling. 1987;**7**:827-833

[4] Hustrulid W, Kuchta M, Martin R. Open Pit Mine Planning and Design— Volume 1: Fundamental. 3rd ed.

London: Taylor and Francis; 2013. p. 995

Engineering. 2nd ed. New York: Wiley-Interscience Publication; 2002. p. 564

[7] Harraz H. Mining Methods: Surface Mining Planning and Design of Open Pit Mining [Internet]. 2016. Available from: https://www.slideshare.net/hzharraz/ surface-mining-planning-and-designof-open-pit-mining [Accessed:

[8] Ascarza W. Mine Tales: Huge Haul Trucks Changed the Face of the Mining Industry. 2014. Available from: https:// tucson.com [Accessed: 15 November

[9] Dessureault S. Equipment Operations Technology, University of Arizona Mining and Geological Engineering Course Notes–2005; 2015. p. 208

[6] Oggeri C, Fenoglio T, Godio A, Vinai R. Overburden management in open pits: Options and limits in large limestone quarries. International Journal of Mining Science and Technology.

In the mountainous and hilly terrains, contour mining is applied. It is also known as mountaintop mining. The mining of flat deposits in these areas follows the contour around the hill and into the hillside up to the economic limits. The extraction becomes difficult with inclination and depth increase. The top of a mountain is removed to recover the ore contained in the mountain that resulted in huge quantity of excess spoil that is placed in valleys that affected the streams flowing within these valleys [21].

Artisanal mining is a small scale mining method, which includes enterprises or individuals that employ workers in developing countries who are poor and have few other options for supporting their families and who usually use manually intensive methods for mining (e.g., panning in case of gold). Artisanal miners use elementary techniques for mineral extraction and often operate under hazardous, laborintensive, highly disorganized, and illegal conditions [20, 22].

#### **Author details**

Awwad H. Altiti, Rami O. Alrawashdeh\* and Hani M. Alnawafleh Mining Engineering Program, College of Engineering, Al-Hussein Bin Talal University, Ma'an, Jordan

\*Address all correspondence to: r\_rawash@yahoo.com.au

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

overburden generally costs at least three times as much as dragline stripping, the dragline is currently implemented for removing overburden from phosphate ore in those mines (**Figure 30**). On the other hand, shovel truck removal of overburden is

as mountaintop mining. The mining of flat deposits in these areas follows the contour around the hill and into the hillside up to the economic limits. The extraction becomes difficult with inclination and depth increase. The top of a mountain is removed to recover the ore contained in the mountain that resulted in huge quantity of excess spoil that is placed in valleys that affected the streams flowing within

In the mountainous and hilly terrains, contour mining is applied. It is also known

Artisanal mining is a small scale mining method, which includes enterprises or individuals that employ workers in developing countries who are poor and have few other options for supporting their families and who usually use manually intensive methods for mining (e.g., panning in case of gold). Artisanal miners use elementary techniques for mineral extraction and often operate under hazardous, labor-

currently used in Attarat oil shale mine (**Figure 31**).

*Mining Techniques - Past, Present and Future*

intensive, highly disorganized, and illegal conditions [20, 22].

Awwad H. Altiti, Rami O. Alrawashdeh\* and Hani M. Alnawafleh

\*Address all correspondence to: r\_rawash@yahoo.com.au

provided the original work is properly cited.

Mining Engineering Program, College of Engineering, Al-Hussein Bin Talal

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

these valleys [21].

**Author details**

**22**

University, Ma'an, Jordan

[1] Wetherelt A, Peter K, Wielen V. Introduction to open pit mining. In: SME Mining Engineering Handbook. 2nd ed. Colorado: Society for Mining, Metallurgy, and Exploration Inc; 2011. p. 2161

[2] Tomakov P, Naumov I. Technology Mechanization and Organization of Surface Mining. 2nd ed. NEDRA: Moscow; 1986. p. 312

[3] Bullivant D. Current surface mining techniques. Journal for the Transportation of Materials in Bulk: Bulk Solids Handling. 1987;**7**:827-833

[4] Hustrulid W, Kuchta M, Martin R. Open Pit Mine Planning and Design— Volume 1: Fundamental. 3rd ed. London: Taylor and Francis; 2013. p. 995

[5] Introductory HH. Mining Engineering. 2nd ed. New York: Wiley-Interscience Publication; 2002. p. 564

[6] Oggeri C, Fenoglio T, Godio A, Vinai R. Overburden management in open pits: Options and limits in large limestone quarries. International Journal of Mining Science and Technology. 2019;**29**(2):217-228

[7] Harraz H. Mining Methods: Surface Mining Planning and Design of Open Pit Mining [Internet]. 2016. Available from: https://www.slideshare.net/hzharraz/ surface-mining-planning-and-designof-open-pit-mining [Accessed: 15 November 2019]

[8] Ascarza W. Mine Tales: Huge Haul Trucks Changed the Face of the Mining Industry. 2014. Available from: https:// tucson.com [Accessed: 15 November 2019]

[9] Dessureault S. Equipment Operations Technology, University of Arizona Mining and Geological Engineering Course Notes–2005; 2015. p. 208

[10] McShane J. Metal Products Advances in Material Hauling for Mining Operations. 2020. Available from: https://www.mcshanemetalprod ucts.com/blog-post/advances-materia l-hauling-mining-operations/ [Accessed: 10 November 2019]

[11] Fleurisson J. Slope design and implementation in open pit mines: Geological and geomechanical approach. Procedia Engineering. 2011; **46**:27-38

[12] Stevens R. Mineral Exploration and Mining Essentials. British Colombia: Pakawau GeoManagement Inc./British Columbia Institute of Technology; 2014. p. 317

[13] Kuter N. Reclamation of Degraded Landscapes Due to Opencast Mining. Cankiri, Turkey: Department of Landscape Architecture, Faculty of Forestry, Cankiri Karatekin University; 2013. DOI: 10.5722/55796

[14] Liu H. Strategic Planning for Dragline Excavation Sequencing [PhD thesis]. Australia: The University of Queensland; 2018. Available from: https://espace.library.uq.edu.au/ [Accessed: 18 April 2020]

[15] Haldar S. Mineral Exploration: Principles and Applications. 2nd ed. Oxford: Elsevier; 2018. p. 378. ISBN: 9780128140222

[16] Brown I. Strip mining. Ch. 10.11. In: Darling P, editor. SME Mining Engineering Handbook. Vol. 1. Colorado: SME; 2011. pp. 1031-1046

[17] Harraz H. Mining Methods: Part I-Surface Mining. 2010. Available from: https://www.researchgate.net/ publication/301824314\_Mining\_ Methods\_Part\_I-Surface\_mining. [Accessed: 15 December 2019]

[18] Tatiya RR. Surface and Underground Excavations*—*Methods, Techniques and Equipment. London: A. A. Balkema Publishers, a member of Taylor & Francis Group plc.; 2005. ISBN: 90 5809 627 0

**Chapter 2**

**Abstract**

**1. Introduction**

**25**

Developments Made for

Geomining Conditions

mass coal production from Indian underground mines.

sagging, rib/snook, breaker-line support, cut-out distance

*and Amit Kumar Singh*

Mechanised Extraction of

Locked-Up Coal Pillars in Indian

Bord and Pillar method of underground mining has been used extensively to develop Indian coal seams into pillars and galleries. This results in only 20–30% recovery of coal and rest coal remain locked up in developed pillars. Indian coalfields are famous in the world for its uniqueness and complexity of the geomining conditions which makes the extraction of the locked-up coal pillars a difficult and hazardous activity using different underground mining methods. Indian mining industry has introduced mechanisation since last 10 years to deal with the various underground rock mechanics issues in order to improve the efficiency and safety during recovery of locked-up coal pillars. But mere introduction of mechanisation did not solve all the rock mechanics problems due to requirement of indigenous design of different involved geotechnical elements for Indian geomining conditions. CSIR-CIMFR is a national research organisation engaged in improving conditions of underground coal mines. It has developed rock mechanics advances, namely, design of irregular shaped heightened rib/snook, roof bolt-based breaker-line support, warning limit of roof sagging, and cut-out distance for continuous miner-based mechanised depillaring. This chapter presents the developments made and highlights challenges to pursue future research studies for mechanised depillaring-based

**Keywords:** continuous miner, mechanised depillaring, rock mechanics issues, roof

Around 96% of the total coal production in India is currently being produced by

mechanised technologies over underground as the former has rock mechanics issues as only slope/dump stability. However, opencast mining method has limitations of

opencast mining method and the contribution of underground mining is on a declining trend from 22% in 2001 to 4% in 2019. Opencast is favoured due to availability of reserves at shallow depth of cover and heavy earth moving

*Ashok Kumar, Dheeraj Kumar, Arun Kumar Singh,*

*Sahendra Ram, Rakesh Kumar, Mudassar Raja*

[19] Liu H. Strategic Planning for Dragline Excavation Sequencing [PhD thesis]. Australia: The University of Queensland; 2018. [Unpublished]

[20] Erdem B, Duran Z, Çelebi N. A model for direct dragline casting in a dipping coal-seam. The Journal of the South African Institute of Mining and Metallurgy. 2004:9-16

[21] Copeland C. Mountaintop Mining: Background on Current Controversies. Congressional Research Service.7-5700; 2015. Available from: www.crs.gov. RS21421

[22] Hinton J, Veiga M, Beinhoff C. Women and artisanal mining: Gender roles and the road ahead. Chapter 11. In: Hilson G, editor. The Socio-Economic Impacts of Artisanal and Small-Scale Mining in Developing Countries. The Netherlands: August Aime Balkema, Swets Publishers; 2003

#### **Chapter 2**

[18] Tatiya RR. Surface and

ISBN: 90 5809 627 0

Metallurgy. 2004:9-16

Swets Publishers; 2003

RS21421

**24**

Underground Excavations*—*Methods, Techniques and Equipment. London: A. A. Balkema Publishers, a member of Taylor & Francis Group plc.; 2005.

*Mining Techniques - Past, Present and Future*

[19] Liu H. Strategic Planning for Dragline Excavation Sequencing [PhD thesis]. Australia: The University of Queensland; 2018. [Unpublished]

[20] Erdem B, Duran Z, Çelebi N. A model for direct dragline casting in a dipping coal-seam. The Journal of the South African Institute of Mining and

[21] Copeland C. Mountaintop Mining: Background on Current Controversies. Congressional Research Service.7-5700; 2015. Available from: www.crs.gov.

[22] Hinton J, Veiga M, Beinhoff C. Women and artisanal mining: Gender roles and the road ahead. Chapter 11. In: Hilson G, editor. The Socio-Economic Impacts of Artisanal and Small-Scale Mining in Developing Countries. The Netherlands: August Aime Balkema,

## Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining Conditions

*Ashok Kumar, Dheeraj Kumar, Arun Kumar Singh, Sahendra Ram, Rakesh Kumar, Mudassar Raja and Amit Kumar Singh*

#### **Abstract**

Bord and Pillar method of underground mining has been used extensively to develop Indian coal seams into pillars and galleries. This results in only 20–30% recovery of coal and rest coal remain locked up in developed pillars. Indian coalfields are famous in the world for its uniqueness and complexity of the geomining conditions which makes the extraction of the locked-up coal pillars a difficult and hazardous activity using different underground mining methods. Indian mining industry has introduced mechanisation since last 10 years to deal with the various underground rock mechanics issues in order to improve the efficiency and safety during recovery of locked-up coal pillars. But mere introduction of mechanisation did not solve all the rock mechanics problems due to requirement of indigenous design of different involved geotechnical elements for Indian geomining conditions. CSIR-CIMFR is a national research organisation engaged in improving conditions of underground coal mines. It has developed rock mechanics advances, namely, design of irregular shaped heightened rib/snook, roof bolt-based breaker-line support, warning limit of roof sagging, and cut-out distance for continuous miner-based mechanised depillaring. This chapter presents the developments made and highlights challenges to pursue future research studies for mechanised depillaring-based mass coal production from Indian underground mines.

**Keywords:** continuous miner, mechanised depillaring, rock mechanics issues, roof sagging, rib/snook, breaker-line support, cut-out distance

#### **1. Introduction**

Around 96% of the total coal production in India is currently being produced by opencast mining method and the contribution of underground mining is on a declining trend from 22% in 2001 to 4% in 2019. Opencast is favoured due to availability of reserves at shallow depth of cover and heavy earth moving mechanised technologies over underground as the former has rock mechanics issues as only slope/dump stability. However, opencast mining method has limitations of

depth and associated environmental concerns. Underground mining is a way forward towards clean coal production technology and sustainable development. Depletion of coal at shallow depth is paving the way towards underground mining. **2. Rock mechanics challenges in mechanised depillaring**

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

virgin coal seams.

addressed indigenously.

**2.1 Irregular shaped heightened rib/snook**

mines the safety and efficiency of the MD.

**27**

Underground mining in India has not boomed to that extent due to the less rock mechanics advances in B&P mining method. Depillaring continues to be one of the most challenging and hazardous activities in underground coal mining due to different accidents by roof/side falls and poor performance of structures. It is the main stage of production with around 60–80% of coal recovery. MD was first introduced in 2003 at Anjan Hill Mine of Chirimiri Area of South Eastern Coalfields Limited a subsidiary of Coal India Limited. Irregular shaped rib/snook created during pillar extraction and resin grouted roof-bolts are used as goaf edge support for the first time in India. Due to non-availability of empirical formulation to design such rib/snook and roof bolts-based goaf edge support, MD achieved mixed results in Indian coalfields. Also, the time interval between flashing of light in auto warning tell-tale instrument and roof fall was recorded to fix a warning threshold limit of roof sagging. It was successful at Anjan Hill Mine and MD was further introduced at a number of Indian coal mines to extract standing coal pillars and

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

It was found that the resin grouted roof-bolts as breaker line support (RBBLS) installed directly at the goaf edge did not work effectively and the roof fall extended inside the working and caused collapse of rib/snook and burial of CM [2, 3]. A small increase in area of rib/snook by 20–40% increased the stand-up time of roof in goaf by 5–10 hours. Hanging roof is a serious problem during MD as it creates the issue of front abutment stress causing goaf encroachment and burial of CM. Safety and productivity are the main concern during the underground mining. Geotechnical investigations found that caveability of overlying strata and size of remnants are the two important factors which affect the safety and productivity. Insufficient knowledge of geological discontinuities further aggravates these issues. Rock mechanics challenges at the goaf edge during MD are very complex which needs to be

Natural supports (pillar/fender/rib/snook/stook) are an important element for

During the retreat rib/snook created are further reduced judiciously for regular caving of roof in the goaf which involves dangerous risk of accident. Narrow rib/ snook crushes easily compared to wider snook and size of snook decides the fall area, pattern and filling. Massive/strong overlying strata are more affected by the rib/snook size compared to weak/laminated strata. The practice of leaving too large and too many rib/snook in the goaf over supports the roof cantilever/beam resulting

the success of MD. Size of pillar remnant is critical for the regular caving of overlying hanging strata in goaf during MD. Different countries used different nomenclature for the remnants like snook/stook 'x'/final stump/rib/narrow fender (**Figure 1**). Risk of sudden major roof falls is reduced by leaving a proper sized rib/ snook against the goaf. It acts like a barrier between the slicing operation and goaf. Pillar is split into two equal halves and each half is called fender/stook. After splitting, one fender keeps supporting the slicing operation in another reduced sized fender. Rib/snook is remains of fender left to temporarily support the cantilevering/ beaming roof to permit safe extraction and fall gradually after the extraction is completed. Stability and competency of fender and rib/snook is important for the maximum possible extraction during MD. Natural supports provide more support to the roof than any artificial designed support (cog/chock/bolt/mobile breaker-line roof support). Interaction between the support (natural/artificial) and roof deter-

Indian coal mining industry had rampantly developed a number of coal seams using Bord and Pillar (B&P) mining method on square/rectangular pillars and galleries with around 20–30% coal recovery as per Regulation 111 of the Coal Mines Regulation [1]. Development of coal seam using B&P mining method requires less technical knowledge of rock mechanics. Depillaring of the developed coal pillars becomes challenging due to complex geomining conditions of Indian coalfields namely nature of roof, geological discontinuities and surface/subsurface structures. Conventional depillaring (CD) using drilling-blasting faced issues of goaf encroachment, high induced stresses and failure of underground structures. Coal producing industries started looking for suitable mass coal producing underground technologies to meet the desired coal production. Longwall mining method was introduced long back in India during 1970s but did not get success due to the direct application of foreign technology in Indian complex geomining conditions without any *in-situ* field investigation.

Continuous miner (CM) based mechanised depillaring (MD) has been introduced as a mass coal producing technology to extract the standing coal pillars. It has proved to be successful in India and CM has been deployed in a number of Indian coal mines and many more are yet to come. It has gained the faith of industry by proving its potential of safety and production. Reason of success of CM based MD in Indian coalfields are indigenous design of different geotechnical elements like irregular shaped heightened rib/snook, roof bolts-based breaker-line as goaf edge support, warning limit of roof sagging in geotechnical instrument and cut-out distance in different geomining conditions. Average daily production from a CM face is around 2000 t which is around 10 times of the daily production from a CD face using drilling-blasting. Success of any underground mining method depends upon the performance of underground structures under extreme difficult high induced stress condition. **Table 1** shows the details of MD during development and depillaring in Indian coalfields using CM.


#### **Table 1.** *Details of mechanised depillaring operations at different Indian coalfields.*

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

#### **2. Rock mechanics challenges in mechanised depillaring**

Underground mining in India has not boomed to that extent due to the less rock mechanics advances in B&P mining method. Depillaring continues to be one of the most challenging and hazardous activities in underground coal mining due to different accidents by roof/side falls and poor performance of structures. It is the main stage of production with around 60–80% of coal recovery. MD was first introduced in 2003 at Anjan Hill Mine of Chirimiri Area of South Eastern Coalfields Limited a subsidiary of Coal India Limited. Irregular shaped rib/snook created during pillar extraction and resin grouted roof-bolts are used as goaf edge support for the first time in India. Due to non-availability of empirical formulation to design such rib/snook and roof bolts-based goaf edge support, MD achieved mixed results in Indian coalfields. Also, the time interval between flashing of light in auto warning tell-tale instrument and roof fall was recorded to fix a warning threshold limit of roof sagging. It was successful at Anjan Hill Mine and MD was further introduced at a number of Indian coal mines to extract standing coal pillars and virgin coal seams.

It was found that the resin grouted roof-bolts as breaker line support (RBBLS) installed directly at the goaf edge did not work effectively and the roof fall extended inside the working and caused collapse of rib/snook and burial of CM [2, 3]. A small increase in area of rib/snook by 20–40% increased the stand-up time of roof in goaf by 5–10 hours. Hanging roof is a serious problem during MD as it creates the issue of front abutment stress causing goaf encroachment and burial of CM. Safety and productivity are the main concern during the underground mining. Geotechnical investigations found that caveability of overlying strata and size of remnants are the two important factors which affect the safety and productivity. Insufficient knowledge of geological discontinuities further aggravates these issues. Rock mechanics challenges at the goaf edge during MD are very complex which needs to be addressed indigenously.

#### **2.1 Irregular shaped heightened rib/snook**

Natural supports (pillar/fender/rib/snook/stook) are an important element for the success of MD. Size of pillar remnant is critical for the regular caving of overlying hanging strata in goaf during MD. Different countries used different nomenclature for the remnants like snook/stook 'x'/final stump/rib/narrow fender (**Figure 1**). Risk of sudden major roof falls is reduced by leaving a proper sized rib/ snook against the goaf. It acts like a barrier between the slicing operation and goaf. Pillar is split into two equal halves and each half is called fender/stook. After splitting, one fender keeps supporting the slicing operation in another reduced sized fender. Rib/snook is remains of fender left to temporarily support the cantilevering/ beaming roof to permit safe extraction and fall gradually after the extraction is completed. Stability and competency of fender and rib/snook is important for the maximum possible extraction during MD. Natural supports provide more support to the roof than any artificial designed support (cog/chock/bolt/mobile breaker-line roof support). Interaction between the support (natural/artificial) and roof determines the safety and efficiency of the MD.

During the retreat rib/snook created are further reduced judiciously for regular caving of roof in the goaf which involves dangerous risk of accident. Narrow rib/ snook crushes easily compared to wider snook and size of snook decides the fall area, pattern and filling. Massive/strong overlying strata are more affected by the rib/snook size compared to weak/laminated strata. The practice of leaving too large and too many rib/snook in the goaf over supports the roof cantilever/beam resulting

depth and associated environmental concerns. Underground mining is a way forward towards clean coal production technology and sustainable development. Depletion of coal at shallow depth is paving the way towards underground mining. Indian coal mining industry had rampantly developed a number of coal seams using Bord and Pillar (B&P) mining method on square/rectangular pillars and galleries with around 20–30% coal recovery as per Regulation 111 of the Coal Mines Regulation [1]. Development of coal seam using B&P mining method requires less technical knowledge of rock mechanics. Depillaring of the developed coal pillars becomes challenging due to complex geomining conditions of Indian coalfields namely nature of roof, geological discontinuities and surface/subsurface structures.

Conventional depillaring (CD) using drilling-blasting faced issues of goaf

any *in-situ* field investigation.

*Mining Techniques - Past, Present and Future*

depillaring in Indian coalfields using CM.

**Gallery width (m)**

A 50–163 33 33 6.6 Sandy shale Split and

G 160–325 35 36 6.0 Sandstone Split and

P 50–120 18.5 19.5 6.6 Shale Christmas

V 50–100 18.5 19.5 6.6 Shale Christmas

*Details of mechanised depillaring operations at different Indian coalfields.*

**Immediate roof**

**Manner of pillar extraction**

slice

slice

tree

tree

**Snook size (m<sup>2</sup> )**

**Roof sagging limit in AWTT (mm)**

26 5 mm as both warning and withdrawal limits

102 5 mm as warning and 10 mm as withdrawal limits

22 5 mm as warning and 8 mm as withdrawal limits

22 5 mm as warning and 8 mm as withdrawal limits

**Cut-out distance (m)**

14 m in split and 10 m in slice

15 m in split and 12 m in slice

12 m in split and 9.5 m in slice

12 m in split and 9.5 m in slice

**Depth Pillar size (m m)**

**Name of mine**

**Table 1.**

**26**

encroachment, high induced stresses and failure of underground structures. Coal producing industries started looking for suitable mass coal producing underground technologies to meet the desired coal production. Longwall mining method was introduced long back in India during 1970s but did not get success due to the direct application of foreign technology in Indian complex geomining conditions without

Continuous miner (CM) based mechanised depillaring (MD) has been introduced as a mass coal producing technology to extract the standing coal pillars. It has proved to be successful in India and CM has been deployed in a number of Indian coal mines and many more are yet to come. It has gained the faith of industry by proving its potential of safety and production. Reason of success of CM based MD in Indian coalfields are indigenous design of different geotechnical elements like irregular shaped heightened rib/snook, roof bolts-based breaker-line as goaf edge support, warning limit of roof sagging in geotechnical instrument and cut-out distance in different geomining conditions. Average daily production from a CM face is around 2000 t which is around 10 times of the daily production from a CD face using drilling-blasting. Success of any underground mining method depends upon the performance of underground structures under extreme difficult high induced stress condition. **Table 1** shows the details of MD during development and

#### **Figure 1.**

*Different sizes of rib/snook created during the conventional and mechanised depillaring (modified after Singh et al. [4]). (a) Manner of extraction and regular shaped rib during conventional depillaring. (b) Single pass extraction/fish-bone/Christmas tree. (c) Splitting and slicing/pocket and fender.*

in increased stand-up time of roof. This results in transfer of abutment stress towards fender and solid pillars in the working. Laminated/weak strata and shallow depth cover strata have less tendency of bridging compared to strong/massive at higher depth of cover. For weaker strata even a small rib/snook acts like a solid pillar at shallow depth of cover.

Small increase in area of rib/snook may lead to increased stand-up time of roof. Different shapes and sizes of rib/snook created during the three different manner of extraction are shown in **Figure 1**. The shape of rib/snook is often irregular in shape due to the manoeuvrability of CM and existing rectangular/square pillars. Shapes and estimation of area of such shapes of rib/snook formed during CD and MD is shown in **Figure 2**. No empirical formula is applicable or available to estimate the strength of such irregular rib/snook **Figure 2(b)** and **(c)**. Seam height, depth of cover and nature of roof strata plays important role in deciding the competency of a given size of rib/snook. A conceptual model is developed for establishing a relationship of stand-up time of different nature of roof with the different sizes of rib/ snook during MD as shown in **Figure 3**.

stability of rib/snook becomes a concern for the safety of men and machineries. Some cases of burial of CM occurred at few mines due to failure of incompetent rib/ snook explained in Singh et al. [2]. Singh et al. [4] conducted a parametric study based on the field studies on numerical models by varying the nature of roof and depth of cover. This study found to be useful in designing a competent rib/snook

*Stand-up time of different nature of roof in goaf with variation with rib/snook area.*

*Area of different shapes and sizes of rib/snook created during the conventional and mechanised depillaring. (a) Shape of snook during conventional depillaring method. (b) Shape of snook during Christmas tree/fish bone*

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

*method. (c) Shape of snook during split and fender method.*

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

during MD.

**29**

**Figure 3.**

**Figure 2.**

Singh et al. [4] studied the performance of rib/snook at different underground mines practising MD at different depths and nature of roof. CM carried out the slicing operation under the shadow of created competent rib/snook. Therefore,

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

#### **Figure 2.**

in increased stand-up time of roof. This results in transfer of abutment stress towards fender and solid pillars in the working. Laminated/weak strata and shallow depth cover strata have less tendency of bridging compared to strong/massive at higher depth of cover. For weaker strata even a small rib/snook acts like a solid

*extraction/fish-bone/Christmas tree. (c) Splitting and slicing/pocket and fender.*

*Different sizes of rib/snook created during the conventional and mechanised depillaring (modified after Singh et al. [4]). (a) Manner of extraction and regular shaped rib during conventional depillaring. (b) Single pass*

Small increase in area of rib/snook may lead to increased stand-up time of roof. Different shapes and sizes of rib/snook created during the three different manner of extraction are shown in **Figure 1**. The shape of rib/snook is often irregular in shape due to the manoeuvrability of CM and existing rectangular/square pillars. Shapes and estimation of area of such shapes of rib/snook formed during CD and MD is shown in **Figure 2**. No empirical formula is applicable or available to estimate the strength of such irregular rib/snook **Figure 2(b)** and **(c)**. Seam height, depth of cover and nature of roof strata plays important role in deciding the competency of a given size of rib/snook. A conceptual model is developed for establishing a relationship of stand-up time of different nature of roof with the different sizes of rib/

Singh et al. [4] studied the performance of rib/snook at different underground mines practising MD at different depths and nature of roof. CM carried out the slicing operation under the shadow of created competent rib/snook. Therefore,

pillar at shallow depth of cover.

*Mining Techniques - Past, Present and Future*

**Figure 1.**

**28**

snook during MD as shown in **Figure 3**.

*Area of different shapes and sizes of rib/snook created during the conventional and mechanised depillaring. (a) Shape of snook during conventional depillaring method. (b) Shape of snook during Christmas tree/fish bone method. (c) Shape of snook during split and fender method.*

**Figure 3.** *Stand-up time of different nature of roof in goaf with variation with rib/snook area.*

stability of rib/snook becomes a concern for the safety of men and machineries. Some cases of burial of CM occurred at few mines due to failure of incompetent rib/ snook explained in Singh et al. [2]. Singh et al. [4] conducted a parametric study based on the field studies on numerical models by varying the nature of roof and depth of cover. This study found to be useful in designing a competent rib/snook during MD.

#### **2.2 Roof bolt-based breaker-line as goaf edge support**

Goaf edge during MD poses a challenging rock mechanics issue especially during the reduction of fender into rib/snook. Rib/snook formed cannot alone act against the goaf encroachment as it needs the support of breaker/hinge-line to break the bridging beam/cantilever roof. Performance of RBBLS in different mines had been monitored visually and also, using instrumented roof bolt. It was found that the position of hinge/breaker-line is affected by the nature of roof rock and size of competent fender/rib/snook/stook 'x', split gallery and out-bye intersections. Function of the hinge/breaker-line is to enhance the strength of rib/snook against caving roof and prevent the encroachment inside the working.

RBBLS forms an important geotechnical element of MD for its success. Pillar/ fender at the goaf edge experienced fracturing of its sides (called spalling) which leads to shifting of position of RBBLS by 0.5–2.0 m towards the out-bye side depending upon the extent of spalling. After shifting the position, the efficiency of RBBLS enhanced (**Figure 4**). Ram et al. [5] designed the roof bolts-based breaker line as goaf edge support in Indian MD coalfields using the field and numerical simulation studies based on parametric variation of nature of roof and depth.

#### **2.3 Warning limit of roof sagging in geotechnical instrument**

Auto warning tell-tale is a geotechnical instrument which has a LED light for flashing in dark environment when the roof sagging crosses the threshold limit fixed in it. There are two important factors which decide success of AWTT in MD, namely, setting of safe roof sagging threshold limit and the fixation of anchorage point. Generally, the anchorage is fixed at a horizon of 10 m in the roof which is found to be a successful practice as the roof below it is vulnerable to failure during local fall after extraction. Roof sagging value is found to be varying in different methods of mining and factors like size of remnant, thickness and elasticity of roof affected it. Therefore, Kumar et al. [6] studied the roof sagging limit set in AWTT at different MD faces. Further, a parametric study to estimate a safe warning roof sagging limit is decided based on field studies and numerical simulation.

A typical observation by AWTT is shown in **Figure 5** indicating the timeinterval between flashing and roof fall in a MD panel. Initially, due to the support by barrier pillar from three sides and solid pillar from one side, the time taken for roof fall is the maximum. As the extraction progresses away from the barrier on dipside, the time-interval between flashing of AWTT and roof fall reduced due to the

formation of cantilever from beam. Variation in recording of roof displacement is studied in a MD panel through tell-tales (auto warning/single height/rotary). Most of the observations of roof sagging is found to be between 11 and 20 mm (**Figure 6**)

*Time-interval between flashing and roof fall in a MD panel measured using auto warning tell-tale.*

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

Rock load height increases with increase in width of a gallery and found to be independent of its height. Cut-out distance defines the productivity of CM; therefore, it becomes an important geotechnical element to be designed in a panel. It is defined as the safe and stable span for a fixed width of gallery excavated by CM in a single lift without application of any applied/reactive support. Field studies are conducted at a number of Indian MD coalfields. It is found that width of the excavated gallery and nature of overlying strata are the two most influencing parameters which affects the cut-out distance to be practised in a given geo-mining

It has been also found that cut-out distance is to be kept different for a develop-

ment and depillaring operations. Lesser rock mechanics issues are encountered during development activity by CM whereas depillaring involves dynamic activity

as recorded from different tell-tales used in the mine.

*Range of roof displacement observed in a panel through tell-tales.*

**2.4 Cut-out distance**

**Figure 5.**

**Figure 6.**

conditions.

**31**

**Figure 4.** *Controlled caving inside the goaf after placement of an efficient breaker line supports at the goaf edge.*

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

**Figure 5.** *Time-interval between flashing and roof fall in a MD panel measured using auto warning tell-tale.*

**Figure 6.**

**2.2 Roof bolt-based breaker-line as goaf edge support**

*Mining Techniques - Past, Present and Future*

caving roof and prevent the encroachment inside the working.

**2.3 Warning limit of roof sagging in geotechnical instrument**

**Figure 4.**

**30**

Goaf edge during MD poses a challenging rock mechanics issue especially during the reduction of fender into rib/snook. Rib/snook formed cannot alone act against the goaf encroachment as it needs the support of breaker/hinge-line to break the bridging beam/cantilever roof. Performance of RBBLS in different mines had been monitored visually and also, using instrumented roof bolt. It was found that the position of hinge/breaker-line is affected by the nature of roof rock and size of competent fender/rib/snook/stook 'x', split gallery and out-bye intersections. Function of the hinge/breaker-line is to enhance the strength of rib/snook against

RBBLS forms an important geotechnical element of MD for its success. Pillar/ fender at the goaf edge experienced fracturing of its sides (called spalling) which leads to shifting of position of RBBLS by 0.5–2.0 m towards the out-bye side depending upon the extent of spalling. After shifting the position, the efficiency of RBBLS enhanced (**Figure 4**). Ram et al. [5] designed the roof bolts-based breaker line as goaf edge support in Indian MD coalfields using the field and numerical simulation studies based on parametric variation of nature of roof and depth.

Auto warning tell-tale is a geotechnical instrument which has a LED light for flashing in dark environment when the roof sagging crosses the threshold limit fixed in it. There are two important factors which decide success of AWTT in MD, namely, setting of safe roof sagging threshold limit and the fixation of anchorage point. Generally, the anchorage is fixed at a horizon of 10 m in the roof which is found to be a successful practice as the roof below it is vulnerable to failure during local fall after extraction. Roof sagging value is found to be varying in different methods of mining and factors like size of remnant, thickness and elasticity of roof affected it. Therefore, Kumar et al. [6] studied the roof sagging limit set in AWTT at different MD faces. Further, a parametric study to estimate a safe warning roof sagging limit is decided based on field studies and numerical simulation.

A typical observation by AWTT is shown in **Figure 5** indicating the timeinterval between flashing and roof fall in a MD panel. Initially, due to the support by barrier pillar from three sides and solid pillar from one side, the time taken for roof fall is the maximum. As the extraction progresses away from the barrier on dipside, the time-interval between flashing of AWTT and roof fall reduced due to the

*Controlled caving inside the goaf after placement of an efficient breaker line supports at the goaf edge.*

*Range of roof displacement observed in a panel through tell-tales.*

formation of cantilever from beam. Variation in recording of roof displacement is studied in a MD panel through tell-tales (auto warning/single height/rotary). Most of the observations of roof sagging is found to be between 11 and 20 mm (**Figure 6**) as recorded from different tell-tales used in the mine.

#### **2.4 Cut-out distance**

Rock load height increases with increase in width of a gallery and found to be independent of its height. Cut-out distance defines the productivity of CM; therefore, it becomes an important geotechnical element to be designed in a panel. It is defined as the safe and stable span for a fixed width of gallery excavated by CM in a single lift without application of any applied/reactive support. Field studies are conducted at a number of Indian MD coalfields. It is found that width of the excavated gallery and nature of overlying strata are the two most influencing parameters which affects the cut-out distance to be practised in a given geo-mining conditions.

It has been also found that cut-out distance is to be kept different for a development and depillaring operations. Lesser rock mechanics issues are encountered during development activity by CM whereas depillaring involves dynamic activity

where overlying strata are highly vulnerable to large induced stresses compared to development. However, it is kept to be a constant value in both development and depillaring operation for easier practice and understanding by the miners. It can be increased during development for faster preparation of the panel and reduced during depillaring for safety and productivity of the mine.

#### **2.5 Thickness of coal seam**

Thickness is a serious issue in Indian coalfields as a major amount of coal is lost due to unplanned development of a seam along roof/floor/middle horizon. A number of thick coal seams in the country are left developed along different horizons locking huge amount of coal [7]. Extraction of full thickness of a thick coal seam at a time is important for Indian underground coal mines. Earlier blasting gallery (BG) method was used by the Indian industry to extract the complete thickness of a thick coal seam in a single lift [8, 9]. But this method failed to improve the safety as well as faster and efficient recovery of coal extraction from BG panels. Height of the pillars at the goaf edge increased from the inbye side due to full extraction of the coal seam thickness during BG. Barrier pillars and pillars at the goaf edge in the panel were vulnerable to goaf encroachment and their premature collapse occurred due to strength dilution by indirect increase in height. Stability of heightened coal pillar was studied by Kumar et al. [10] using numerical simulation and established a relation between strength estimated through numerical modelling with that of CSIR-CIMFR formula, shown below.

$$\mathbf{S\_{CMRI}} = \mathbf{1.28}\,\mathbf{S\_{NM}} - \mathbf{9.5} \tag{1}$$

Experiences of working at higher depth are important for the Indian industry as it is planning to go deeper for coal extraction in near future. Recent experiences gained by IGN, Czech Republic in collaboration with CSIR-CIMFR, are beneficial for the Indian mining industry. Underground structures at higher depth of cover needs to be designed judiciously for the maximum coal recovery by leaving less amount of coal in the goaf. Further, it would not create the issues of spontaneous heating, goaf encroachment and coal bump. Also, there is a need to design an optimum barrier pillar at higher depth of cover exceeding 300 m which crushes with retreat of working in the panel. Concept of rib/snook design in MD needs to be used for design for pillar at higher depth of cover. It should be capable to support the roof and stand stable till the extraction is over under its shadow and should fail in a controlled manner in goaf due to increase stresses. Following such design norm would help in sustainable development with maximum utilisation of resources with

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

Different nature of overlying strata has different unsupported span for its caving. During first row of coal pillar extraction in MD, the goaf span is not sufficient for caving and therefore it is suggested to go for the maximum possible extraction due to the support from barrier and solid pillars from all the sides. Generally, roof fall is experienced when the length of the goaf span is equal to the panel length. Presence of thick difficult to cave massive competent strata does not cave even after this span due to the higher strength and thickness [14]. Hanging of such strata creates issues of goaf encroachment, over riding of pillars and sometimes air blast

Different techniques have been used to deal with such strata during MD. MD is practised in Pinoura and Vindhya mine having easily caveable roof with frequent roof fall to VK-7 and Churcha mine having massive Deccan trap/sill delaying roof fall. Bulking factor plays a major role in caving of roof and estimation of subsidence on the surface. Sometimes the difficult to cave massive strata is located after a parting in the roof. In this case the bulking of the caved material fills the void. If the roof is difficult to cave-in and present as immediate strata then it remains hanging in goaf for a longer span of exposure and remedial measures like induced blasting or small panel (non-effective width) technique is adopted. High induced stress is created due to large span of overhang in the goaf. **Figure 7** shows the area of

The value of caveability index (*I*) decides the easiness/difficulty hanging overlying strata to cave in goaf. It was established by Sarkar and Singh [15] for characterisation of the overlying strata in Longwall mining method. It is defined as:

<sup>5</sup> (2)

, *l* = average length of core in

*<sup>I</sup>* <sup>¼</sup> *<sup>σ</sup><sup>l</sup> n T*<sup>0</sup>*:*<sup>5</sup>

cm,*T* = thickness of the strong bed in m, and the factor *n* has a value of 1.2 in the case of uniformly massive rocks with a weighted average of RQD of 80% and above.

This caveability index developed for Longwall mining is not applicable in case of MD as it has a number of openings around the goaf edge and left-out ribs/snooks. There is a need to develop such index for MD which would help to extract coal by

less wastage.

**2.7 Goaf span and caveability**

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

and coal/rock bump.

In all other cases *n* = 1.

**33**

exposure and progressive area of fall in a MD panel.

where *σ* = uniaxial compressive strength in kg/cm<sup>2</sup>

CM especially under extremely difficult to cave massive strata.

where SNM = pillar strength estimated through numerical modelling and SCMRI = pillar strength estimated through empirical formulation.

Modification in manner of pillar extraction by CM helped in complete recovery of a 6 m thick coal at a time. CM extracted the floor coal up to 1.5–2.0 m during retreat in a slice. This created an issue of heightened irregular shaped rib/snook. Stability of such heightened rib/snook during MD was studied by Kumar et al. [7] by changing the heights of rib/snook from 3.0 to 6.0 m for a given area, nature of roof and depth. It needs to be further studied by changing the depth of cover and nature of roof with the variation in heights of rib/snook.

#### **2.6 Issues of stress and pillar design at higher depth**

Depth is a major issue for design of underground mining structures as B&P mining method is no more feasible at overburden cover greater than 400 m. Longwall is feasible at such depth of cover but indigenous design of barrier/chain/ rib pillar is important. A new concept of barrierless design of longwall panel has been introduced in China. Similar concept can be used in B&P for the design of barrier pillars. Optimum design of pillars helps in maximum coal recovery and minimum wastage as left-out remnants in goaf. Worldwide available empirical formula for estimation of pillar strength does not explain the effect of depth on their strength except Sheorey [11]. Higher depth creates the case of high value of vertical in-situ stress which affects the performance of underground structures [12]. Available empirical formulation becomes redundant for the strength estimation of underground structures at higher depth. CSIR-CIMFR empirical strength formula may be used to estimate pillar strength but it did not consider the failed and stable cases of pillar at such high depth of cover [13].

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

Experiences of working at higher depth are important for the Indian industry as it is planning to go deeper for coal extraction in near future. Recent experiences gained by IGN, Czech Republic in collaboration with CSIR-CIMFR, are beneficial for the Indian mining industry. Underground structures at higher depth of cover needs to be designed judiciously for the maximum coal recovery by leaving less amount of coal in the goaf. Further, it would not create the issues of spontaneous heating, goaf encroachment and coal bump. Also, there is a need to design an optimum barrier pillar at higher depth of cover exceeding 300 m which crushes with retreat of working in the panel. Concept of rib/snook design in MD needs to be used for design for pillar at higher depth of cover. It should be capable to support the roof and stand stable till the extraction is over under its shadow and should fail in a controlled manner in goaf due to increase stresses. Following such design norm would help in sustainable development with maximum utilisation of resources with less wastage.

#### **2.7 Goaf span and caveability**

where overlying strata are highly vulnerable to large induced stresses compared to development. However, it is kept to be a constant value in both development and depillaring operation for easier practice and understanding by the miners. It can be increased during development for faster preparation of the panel and reduced

Thickness is a serious issue in Indian coalfields as a major amount of coal is lost due to unplanned development of a seam along roof/floor/middle horizon. A number of thick coal seams in the country are left developed along different horizons locking huge amount of coal [7]. Extraction of full thickness of a thick coal seam at a time is important for Indian underground coal mines. Earlier blasting gallery (BG) method was used by the Indian industry to extract the complete thickness of a thick coal seam in a single lift [8, 9]. But this method failed to improve the safety as well as faster and efficient recovery of coal extraction from BG panels. Height of the pillars at the goaf edge increased from the inbye side due to full extraction of the coal seam thickness during BG. Barrier pillars and pillars at the goaf edge in the panel were vulnerable to goaf encroachment and their premature collapse occurred due to strength dilution by indirect increase in height. Stability of heightened coal pillar was studied by Kumar et al. [10] using numerical simulation and established a relation between strength estimated through numerical modelling with that of

where SNM = pillar strength estimated through numerical modelling and

Modification in manner of pillar extraction by CM helped in complete recovery of a 6 m thick coal at a time. CM extracted the floor coal up to 1.5–2.0 m during retreat in a slice. This created an issue of heightened irregular shaped rib/snook. Stability of such heightened rib/snook during MD was studied by Kumar et al. [7] by changing the heights of rib/snook from 3.0 to 6.0 m for a given area, nature of roof and depth. It needs to be further studied by changing the depth of cover and

Depth is a major issue for design of underground mining structures as B&P mining method is no more feasible at overburden cover greater than 400 m. Longwall is feasible at such depth of cover but indigenous design of barrier/chain/ rib pillar is important. A new concept of barrierless design of longwall panel has been introduced in China. Similar concept can be used in B&P for the design of barrier pillars. Optimum design of pillars helps in maximum coal recovery and minimum wastage as left-out remnants in goaf. Worldwide available empirical formula for estimation of pillar strength does not explain the effect of depth on their strength except Sheorey [11]. Higher depth creates the case of high value of vertical in-situ stress which affects the performance of underground structures [12]. Available empirical formulation becomes redundant for the strength estimation of underground structures at higher depth. CSIR-CIMFR empirical strength formula may be used to estimate pillar strength but it did not consider the failed and stable

SCMRI = pillar strength estimated through empirical formulation.

nature of roof with the variation in heights of rib/snook.

**2.6 Issues of stress and pillar design at higher depth**

cases of pillar at such high depth of cover [13].

**32**

*SCMRI* ¼ 1*:*28 *SNM* � 9*:*5 (1)

during depillaring for safety and productivity of the mine.

**2.5 Thickness of coal seam**

*Mining Techniques - Past, Present and Future*

CSIR-CIMFR formula, shown below.

Different nature of overlying strata has different unsupported span for its caving. During first row of coal pillar extraction in MD, the goaf span is not sufficient for caving and therefore it is suggested to go for the maximum possible extraction due to the support from barrier and solid pillars from all the sides. Generally, roof fall is experienced when the length of the goaf span is equal to the panel length. Presence of thick difficult to cave massive competent strata does not cave even after this span due to the higher strength and thickness [14]. Hanging of such strata creates issues of goaf encroachment, over riding of pillars and sometimes air blast and coal/rock bump.

Different techniques have been used to deal with such strata during MD. MD is practised in Pinoura and Vindhya mine having easily caveable roof with frequent roof fall to VK-7 and Churcha mine having massive Deccan trap/sill delaying roof fall. Bulking factor plays a major role in caving of roof and estimation of subsidence on the surface. Sometimes the difficult to cave massive strata is located after a parting in the roof. In this case the bulking of the caved material fills the void. If the roof is difficult to cave-in and present as immediate strata then it remains hanging in goaf for a longer span of exposure and remedial measures like induced blasting or small panel (non-effective width) technique is adopted. High induced stress is created due to large span of overhang in the goaf. **Figure 7** shows the area of exposure and progressive area of fall in a MD panel.

The value of caveability index (*I*) decides the easiness/difficulty hanging overlying strata to cave in goaf. It was established by Sarkar and Singh [15] for characterisation of the overlying strata in Longwall mining method. It is defined as:

$$I = \frac{\sigma l^n T^{0.5}}{5} \tag{2}$$

where *σ* = uniaxial compressive strength in kg/cm<sup>2</sup> , *l* = average length of core in cm,*T* = thickness of the strong bed in m, and the factor *n* has a value of 1.2 in the case of uniformly massive rocks with a weighted average of RQD of 80% and above. In all other cases *n* = 1.

This caveability index developed for Longwall mining is not applicable in case of MD as it has a number of openings around the goaf edge and left-out ribs/snooks. There is a need to develop such index for MD which would help to extract coal by CM especially under extremely difficult to cave massive strata.

**2.9 Determination of in situ strength of rock mass**

under design which is vulnerable to fail.

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

sudden caving lead to sometimes air blast.

with depth of cover and nature of roof strata.

**3. Rock mechanics advances in mechanised depillaring**

depth of cover.

issues.

**35**

**3.1 Design of rib/snook**

**2.10 Rock burst/coal bump**

It is easier to estimate the physico-mechanical properties of coal and rock in the laboratory using different rock testing equipment. These properties do not reflect the actual properties of in-situ coal/rock mass. There is available Sheorey failure criterion but it is age old and needs to be re-established for the higher depth of cover cases. Also, the strength estimated in laboratory are on a higher side and if these are considered for design of underground structures then there are likely chances of an

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

Strength of rock mass is important for the stability of underground structures in rock and its realistic assessment for coal measure strata presents a unique challenge. Rock mass classifications have tried to quantify the behaviour of the rock mass. Failure criterion is helpful in prediction of strength of rock mass. But, the anisotropic and inhomogeneous behaviour of coal pillar restricts the scope of rock mass failure criteria for higher depth of cover. There is a need to revisit RMR classification system for failure criteria of intact coal measure formations at higher

Stress concentration on underground structures results into accumulation of strain energy inside it resulting into coal bump/rock burst. Coal measure formations have the capability to store large amount of strain energy before failing. It involves the violent failure of rock/coal around an excavation causing severe injury to the miners. Indian coalfields have rare experience of dealing with coal bump/rock burst due to working under moderate nature of roof at shallow depth of cover. Some incidences of coal bump/rock burst have been experienced due to hanging of overlying strata for a longer span in goaf after pillar extraction which creates high abutment stresses over the solid pillars. It is difficult to deal with such strata as their

Deep coal mines with massive/strong roof and high stress-conditions experience coal bump/rock burst. Severity of the rock bump increases with increase in depth and stress. Instrumentation and monitoring using geotechnical instruments and micro seismic methods are helpful in understanding and prevention of such occurrences. Energy stored depends upon the physico-mechanical properties of strata. Various destressing techniques have been practised worldwide to deal with such

Parametric study by varying the nature of roof and depth of cover was carried out in FLAC3D by Singh et al. [4] to estimate the size of irregular shaped rib/snook during MD of existing square/rectangular shaped pillars. Further, height of rib was also varied [7] during extraction of complete thickness of a thick coal seam at a time using numerical simulation to estimate a stable competent size. Results of field and numerical simulation were used to estimate a competent rib/snook. Conceptual model was formulated to have a general idea about variation in size of rib/snook

Area of competent sizes of ribs/snooks with variation in depth of cover and

nature of the roof strata are analysed through a multivariate regression. A

**Figure 7.** *Details of area of exposure and roof falls occurred in MD panel.*

#### **2.8 Geological discontinuities under influence of in-situ stress**

Underground mining operation has witnessed failure of roof during widening and heightening of the developed galleries for adaptability and manoeuvrability of CM (**Figure 8**). This failure occurs due to hidden joints/slips with wash-outs, intercalation, and cross-stratification of shale and sandstone (**Figure 8**). Further, this failure was controlled by using the appropriate support system as per the results of numerical simulation and field investigations. Support becomes an important element under such disturbed nature of roof. Artificial supports in the immediate roof are installed generally after a length of 12 m (cut-out distance of CM) in a gallery width of 6 m. Geological discontinuities (hidden slips, wash-outs, crossstratifications and intercalations of shale and sandstone) in immediate roof strata affected the advancement of drivages using CM in a panel. Freshly exposed immediate roof strata up to 1.8 m failed over the remotely operated CM. The local fall was dangerous to the drivages as it affected the safety, production and productivity of the mine. After the roof fall, cut-out distance was reduced to 4 m but the roof instability continued in the drivages. Further, support system was redesigned (increased density and length of bolts with wire mesh) to successfully control the roof instability for the reduced cut-out distance of 4 m.

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

#### **2.9 Determination of in situ strength of rock mass**

It is easier to estimate the physico-mechanical properties of coal and rock in the laboratory using different rock testing equipment. These properties do not reflect the actual properties of in-situ coal/rock mass. There is available Sheorey failure criterion but it is age old and needs to be re-established for the higher depth of cover cases. Also, the strength estimated in laboratory are on a higher side and if these are considered for design of underground structures then there are likely chances of an under design which is vulnerable to fail.

Strength of rock mass is important for the stability of underground structures in rock and its realistic assessment for coal measure strata presents a unique challenge. Rock mass classifications have tried to quantify the behaviour of the rock mass. Failure criterion is helpful in prediction of strength of rock mass. But, the anisotropic and inhomogeneous behaviour of coal pillar restricts the scope of rock mass failure criteria for higher depth of cover. There is a need to revisit RMR classification system for failure criteria of intact coal measure formations at higher depth of cover.

#### **2.10 Rock burst/coal bump**

**2.8 Geological discontinuities under influence of in-situ stress**

*Details of area of exposure and roof falls occurred in MD panel.*

*Mining Techniques - Past, Present and Future*

**Figure 7.**

**Figure 8.**

**34**

roof instability for the reduced cut-out distance of 4 m.

Underground mining operation has witnessed failure of roof during widening and heightening of the developed galleries for adaptability and manoeuvrability of CM (**Figure 8**). This failure occurs due to hidden joints/slips with wash-outs, intercalation, and cross-stratification of shale and sandstone (**Figure 8**). Further, this failure was controlled by using the appropriate support system as per the results of numerical simulation and field investigations. Support becomes an important element under such disturbed nature of roof. Artificial supports in the immediate roof are installed generally after a length of 12 m (cut-out distance of CM) in a gallery width of 6 m. Geological discontinuities (hidden slips, wash-outs, crossstratifications and intercalations of shale and sandstone) in immediate roof strata affected the advancement of drivages using CM in a panel. Freshly exposed immediate roof strata up to 1.8 m failed over the remotely operated CM. The local fall was dangerous to the drivages as it affected the safety, production and productivity of the mine. After the roof fall, cut-out distance was reduced to 4 m but the roof instability continued in the drivages. Further, support system was redesigned (increased density and length of bolts with wire mesh) to successfully control the

*Wash-outs exposed in the roof of dip rise gallery reduced the cut-out distance of CM during development.*

Stress concentration on underground structures results into accumulation of strain energy inside it resulting into coal bump/rock burst. Coal measure formations have the capability to store large amount of strain energy before failing. It involves the violent failure of rock/coal around an excavation causing severe injury to the miners. Indian coalfields have rare experience of dealing with coal bump/rock burst due to working under moderate nature of roof at shallow depth of cover. Some incidences of coal bump/rock burst have been experienced due to hanging of overlying strata for a longer span in goaf after pillar extraction which creates high abutment stresses over the solid pillars. It is difficult to deal with such strata as their sudden caving lead to sometimes air blast.

Deep coal mines with massive/strong roof and high stress-conditions experience coal bump/rock burst. Severity of the rock bump increases with increase in depth and stress. Instrumentation and monitoring using geotechnical instruments and micro seismic methods are helpful in understanding and prevention of such occurrences. Energy stored depends upon the physico-mechanical properties of strata. Various destressing techniques have been practised worldwide to deal with such issues.

#### **3. Rock mechanics advances in mechanised depillaring**

#### **3.1 Design of rib/snook**

Parametric study by varying the nature of roof and depth of cover was carried out in FLAC3D by Singh et al. [4] to estimate the size of irregular shaped rib/snook during MD of existing square/rectangular shaped pillars. Further, height of rib was also varied [7] during extraction of complete thickness of a thick coal seam at a time using numerical simulation to estimate a stable competent size. Results of field and numerical simulation were used to estimate a competent rib/snook. Conceptual model was formulated to have a general idea about variation in size of rib/snook with depth of cover and nature of roof strata.

Area of competent sizes of ribs/snooks with variation in depth of cover and nature of the roof strata are analysed through a multivariate regression. A

relationship is developed based on the analysis to estimate a competent size of the rib/snook (S), which is given as:

$$\mathbf{S} = \mathbf{0}.\mathbf{S}2 \, H^{0.74} \, \text{ } R^{0.23} \text{ m}^2 \tag{3}$$

studies in FLAC3D by fixing the allowable range of roof sagging to 5 mm (**Figure 9**). Roof sagging values for a 6 m width of gallery by varying the cut-out distances are shown in **Figure 9** on numerical models. **Figure 9** also depicts that the cut-out distance can be further extended beyond 12 m during development using CM for

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

Based on the results of numerical model and field studies, a relationship is established to estimate the cut-out distance with variation in nature of roof and

where S is the length of cut-out distance (m), W = width of gallery (m), and

Apart from abovementioned issues for B&P mining method using CM based MD, there are challenges of rock mechanics in Indian coalfields at higher depth of cover for the characterisation of rock mass, response of underground structures to high in-situ stresses, design of underground structures, economics, subsidence, complete extraction of difficult coal seam at a time, failure criterion of rock mass, fixation of warning limit for stress and convergence in different geotechnical

Despite being the second largest producer of coal in the world, Longwall top coal caving method of mining is still not practised in Indian coalfields whereas China produces around 90% of the coal using this technology. Most of the Indian coal is being produced using opencast method which is not sustainable for longer duration

*Roof sagging value for different cut-out distance in FLAC3D. (a) 9 m, (b) 10 m, (c) 11 m, and (d) 12 m.*

*S* ¼ 14*:*61 þ 1*:*98E � 2*:*12W (9)

faster extraction.

gallery width, which is given as:

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

E = elastic modulus of immediate roof (GPa).

**4. Future rock mechanics issues**

instrumentation and so forth.

**Figure 9.**

**37**

where H = depth of cover (m) and R = CMRI-RMR.

#### **3.2 Design of goaf edge support**

Rock load height (RLH) estimated at the goaf edge using numerical models with variation in RMR and depth of cover and analysed using multivariate regression by Ram et al. [5]. Based on field studies and numerical simulation observations, relationships are developed for the design of RBBLS at three different locations around the goaf edge which are given below.

For 0 m out-bye from goaf edge

$$RLH = \mathbf{11.67} \, H^{0.58} \, R^{-1.14} \tag{4}$$

For 1 m out-bye from goaf edge

$$\text{RLH} = \text{66.32 } H^{0.31} \text{ R}^{-1.26} \tag{5}$$

For 2 m out-bye from goaf edge

$$RLH = \textbf{115.22} \, H^{0.12} \, R^{-1.20} \,\tag{6}$$

#### **3.3 Prediction of roof sagging limit for roof fall**

Kumar et al. [6] did a multivariate analysis of the roof sagging recorded from the numerical models with variation in thickness and elastic modulus of immediate roof, size of remnants and distance from the goaf edge. This analysis helped in derivation of an Eq. 9 to calculate the limiting roof sagging value as:

$$\mathbf{C} = 2\mathbf{6.63} - \mathbf{0.12D} - \mathbf{1.12E} - \mathbf{0.14A} + \mathbf{0.23T} \tag{7}$$

where C is the roof sagging observed in model (mm), D is the goaf edge distance (m), E is the elastic modulus of immediate roof (GPa), A is the size of remnants left in or around goaf edge (m<sup>2</sup> ), and T is the immediate roof thickness (m).

Taking into account the anisotropic and heterogeneous natures of rock, a safety factor of 2 is selected for fixation of the sagging value for a warning limit in AWTT which is given as:

$$\mathbf{S} = \mathbf{0}.\mathbf{5C} \tag{8}$$

where S is the warning value of roof sagging (mm) to be fixed in an AWTT.

#### **3.4 Design of cut-out distance**

CM does not damage the surrounding roof like drilling-blasting during cutting of coal. Cut-out distance in field has been practised based on trial and error in field. Numerical models based on a safe and stable roof sagging value of 5 mm are used to study the cut-out distance with varying nature of roof and width of gallery [7]. Elastic constitutive model is used to study the cut-out distance based on field

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

studies in FLAC3D by fixing the allowable range of roof sagging to 5 mm (**Figure 9**). Roof sagging values for a 6 m width of gallery by varying the cut-out distances are shown in **Figure 9** on numerical models. **Figure 9** also depicts that the cut-out distance can be further extended beyond 12 m during development using CM for faster extraction.

Based on the results of numerical model and field studies, a relationship is established to estimate the cut-out distance with variation in nature of roof and gallery width, which is given as:

$$\mathbf{S} = \mathbf{1}4.6\mathbf{1} + \mathbf{1}.98\mathbf{E} - 2.\mathbf{1}2\mathbf{W} \tag{9}$$

where S is the length of cut-out distance (m), W = width of gallery (m), and E = elastic modulus of immediate roof (GPa).

#### **4. Future rock mechanics issues**

relationship is developed based on the analysis to estimate a competent size of the

Rock load height (RLH) estimated at the goaf edge using numerical models with variation in RMR and depth of cover and analysed using multivariate regression by Ram et al. [5]. Based on field studies and numerical simulation observations, relationships are developed for the design of RBBLS at three different locations around

Kumar et al. [6] did a multivariate analysis of the roof sagging recorded from the numerical models with variation in thickness and elastic modulus of immediate roof, size of remnants and distance from the goaf edge. This analysis helped in

where C is the roof sagging observed in model (mm), D is the goaf edge distance (m), E is the elastic modulus of immediate roof (GPa), A is the size of remnants left

Taking into account the anisotropic and heterogeneous natures of rock, a safety factor of 2 is selected for fixation of the sagging value for a warning limit in AWTT

where S is the warning value of roof sagging (mm) to be fixed in an AWTT.

CM does not damage the surrounding roof like drilling-blasting during cutting of coal. Cut-out distance in field has been practised based on trial and error in field. Numerical models based on a safe and stable roof sagging value of 5 mm are used to study the cut-out distance with varying nature of roof and width of gallery [7]. Elastic constitutive model is used to study the cut-out distance based on field

derivation of an Eq. 9 to calculate the limiting roof sagging value as:

where H = depth of cover (m) and R = CMRI-RMR.

*<sup>S</sup>* <sup>¼</sup> <sup>0</sup>*:*<sup>52</sup> *<sup>H</sup>*0*:*<sup>74</sup> *<sup>R</sup>*0*:*<sup>23</sup> <sup>m</sup><sup>2</sup> (3)

*RLH* <sup>¼</sup> <sup>11</sup>*:*<sup>67</sup> *<sup>H</sup>*<sup>0</sup>*:*<sup>58</sup> *<sup>R</sup>*�1*:*<sup>14</sup> (4)

*RLH* <sup>¼</sup> <sup>66</sup>*:*<sup>32</sup> *<sup>H</sup>*<sup>0</sup>*:*<sup>31</sup> *<sup>R</sup>*�1*:*<sup>26</sup> (5)

*RLH* <sup>¼</sup> <sup>115</sup>*:*<sup>22</sup> *<sup>H</sup>*<sup>0</sup>*:*<sup>12</sup> *<sup>R</sup>*�1*:*<sup>20</sup> (6)

*C* ¼ 26*:*63 � 0*:*12D � 1*:*12E � 0*:*14A þ 0*:*23T (7)

), and T is the immediate roof thickness (m).

*S* ¼ 0*:*5C (8)

rib/snook (S), which is given as:

*Mining Techniques - Past, Present and Future*

**3.2 Design of goaf edge support**

the goaf edge which are given below. For 0 m out-bye from goaf edge

For 1 m out-bye from goaf edge

For 2 m out-bye from goaf edge

in or around goaf edge (m<sup>2</sup>

**3.4 Design of cut-out distance**

which is given as:

**36**

**3.3 Prediction of roof sagging limit for roof fall**

Apart from abovementioned issues for B&P mining method using CM based MD, there are challenges of rock mechanics in Indian coalfields at higher depth of cover for the characterisation of rock mass, response of underground structures to high in-situ stresses, design of underground structures, economics, subsidence, complete extraction of difficult coal seam at a time, failure criterion of rock mass, fixation of warning limit for stress and convergence in different geotechnical instrumentation and so forth.

Despite being the second largest producer of coal in the world, Longwall top coal caving method of mining is still not practised in Indian coalfields whereas China produces around 90% of the coal using this technology. Most of the Indian coal is being produced using opencast method which is not sustainable for longer duration

**Figure 9.**

*Roof sagging value for different cut-out distance in FLAC3D. (a) 9 m, (b) 10 m, (c) 11 m, and (d) 12 m.*

due to its different limitations. Solutions to these future problems lie in carrying out R&D for each such issue on priority basis for the Indian coalfields.

#### **5. Conclusions and recommendations**

Mechanised depillaring using continuous miner technology has proven its potential in improvement of production and safety since last 10 years. A number of Indian coal mines are preferring mechanised depillaring over conventional technique to extract the locked-up coal pillars. Field study found that geo-mining conditions and design of geotechnical structures created during mechanised depillaring affect the performance of this mass coal producing technology. Rock mechanics developments in design of geo technical such as breaker-line support, rib/snook, cut-out distance/lift length and determination of roof sagging limit in instruments at the goaf edges has improved the performance of mechanised depillaring operations. However, rock mechanics issues like complete extraction of a thick coal seam, large span of overhang, caveability of difficult overlying strata, geological discontinuities, depth of working and pillar design at higher depth remains a challenge for this technology. Efforts are being made to deal with these issues in Indian coalfields as per their confrontation.

#### **Acknowledgements**

The authors are obliged to the Director of CSIR-Central Institute of Mining and Fuel Research, Dhanbad, and the Director of Indian Institute of Technology (Indian School of Mines), Dhanbad, for their permission to publish this chapter. The authors also give their due regards to the mine management of different Indian coalfields for the support during field studies. The views expressed in this chapter are that of the authors and do not necessarily reflect the opinion of their organisations.

**Author details**

\*, Dheeraj Kumar<sup>2</sup>

(CSIR-CIMFR), Dhanbad, Jharkhand, India

of Mines), Dhanbad, Jharkhand, India

provided the original work is properly cited.

, Arun Kumar Singh<sup>1</sup>

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

1 Rockmass Characterisation and Innovative Mining Methods Section, Council of Scientific and Industrial Research-Central Institute of Mining and Fuel Research

2 Department of Mining Engineering, Indian Institute of Technology (Indian School

\*Address all correspondence to: ashok.bhu.min09@gmail.com; ashok@cimfr.nic.in

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

, Mudassar Raja<sup>1</sup> and Amit Kumar Singh<sup>1</sup>

, Sahendra Ram<sup>1</sup>

,

Ashok Kumar<sup>1</sup>

Rakesh Kumar<sup>1</sup>

**39**

#### **Conflict of interest**

The authors declare no conflict of interest.

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

#### **Author details**

due to its different limitations. Solutions to these future problems lie in carrying out

Mechanised depillaring using continuous miner technology has proven its potential in improvement of production and safety since last 10 years. A number of Indian coal mines are preferring mechanised depillaring over conventional technique to extract the locked-up coal pillars. Field study found that geo-mining conditions and design of geotechnical structures created during mechanised depillaring affect the performance of this mass coal producing technology. Rock mechanics developments in design of geo technical such as breaker-line support, rib/snook, cut-out distance/lift length and determination of roof sagging limit in instruments at the goaf edges has improved the performance of mechanised depillaring operations. However, rock mechanics issues like complete extraction of a thick coal seam, large span of overhang, caveability of difficult overlying strata, geological discontinuities, depth of working and pillar design at higher depth remains a challenge for this technology. Efforts are being made to deal with these

The authors are obliged to the Director of CSIR-Central Institute of Mining and Fuel Research, Dhanbad, and the Director of Indian Institute of Technology (Indian School of Mines), Dhanbad, for their permission to publish this chapter. The authors also give their due regards to the mine management of different Indian

coalfields for the support during field studies. The views expressed in this chapter are that of the authors and do not necessarily reflect the opinion of their

R&D for each such issue on priority basis for the Indian coalfields.

**5. Conclusions and recommendations**

*Mining Techniques - Past, Present and Future*

issues in Indian coalfields as per their confrontation.

The authors declare no conflict of interest.

**Acknowledgements**

organisations.

**38**

**Conflict of interest**

Ashok Kumar<sup>1</sup> \*, Dheeraj Kumar<sup>2</sup> , Arun Kumar Singh<sup>1</sup> , Sahendra Ram<sup>1</sup> , Rakesh Kumar<sup>1</sup> , Mudassar Raja<sup>1</sup> and Amit Kumar Singh<sup>1</sup>

1 Rockmass Characterisation and Innovative Mining Methods Section, Council of Scientific and Industrial Research-Central Institute of Mining and Fuel Research (CSIR-CIMFR), Dhanbad, Jharkhand, India

2 Department of Mining Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, India

\*Address all correspondence to: ashok.bhu.min09@gmail.com; ashok@cimfr.nic.in

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] The Coal Mines Regulation. Published in The Gazette of India: Extraordinary issued by Ministry of Labour and Employment, Part- II-Section 3(i). 2017. pp. 160-280

[2] Singh AK, Kumar A, Kumar D, Singh R, Ram S, Kumar R, et al. Coal pillar extraction under weak roof. Mining, Metallurgy & Exploration. 2020. DOI: 10.1007/s42461-020- 00277-8

[3] Kumar A, Kumar D, Verma AK, Singh AK, Ram S, Kumar R. Influence of overlying roof strata on rib design in mechanised depillaring. Journal of The Geological Society of India. 2018;**91**(3): 341-347. DOI: 10.1007/s12594-018- 0860-7

[4] Singh R, Kumar A, Singh AK, Coggan J, Ram S. Rib/snook design in mechanised depillaring of rectangular/ square pillars. International Journal of Rock Mechanics and Mining Sciences. 2016;**84**:119-129. DOI: 10.1016/j. ijrmms.2016.02.008

[5] Ram S, Kumar D, Singh AK, Kumar A, Singh R. Field and numerical modelling studies for an efficient placement of roof bolts as breaker line support. International Journal of Rock Mechanics and Mining Sciences. 2017; **93**:152-162. DOI: 10.1016/j. ijrmms.2017.01.013

[6] Kumar A, Kumar D, Singh AK, Ram S, Kumar R, Gautam A, et al. Roof sagging limit in an early warning system for safe coal pillar extraction. International Journal of Rock Mechanics and Mining Sciences. 2019;**123**:104131. DOI: 10.1016/j.ijrmms.2019.104131

[7] Kumar A, Kumar D, Singh AK, Ram S, Kumar R, Singh AK, et al. Strength estimation of irregular shaped heightened rib/snook for mechanised

depillaring. In: Proceedings of 8th Asian Mining Congress (AMC); 6-9 November 2019; Kolkata, India. MGMI; 2019. pp. 529-538

Caveability assessment of a hanging overlying massive Deccan trap and its effect on underground. Insights in Mining Science and Technology. 2019;

*DOI: http://dx.doi.org/10.5772/intechopen.93636*

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining…*

[15] Sarkar SK, Singh B. Longwall Mining in India. Dhanbad: Sunanda

**1**(3):50-60

Sarkar; 1985

**41**

[8] Kumar R, Mishra AK, Singh AK, Singh AK, Ram S, Singh R. Depillaring of total thickness of a thick coal seam in a single lift using cable bolts: A case study. International Journal of Mining Science and Technology. 2015;**25**(6): 885-896

[9] Kumar R, Singh AK, Mishra AK, Singh R. Underground mining of thick coal seams. International Journal of Mining Science and Technology. 2016; **26**(2):223-233

[10] Kumar A, Kumar R, Singh AK, Ram S, Singh PK, Singh R. Numerical modelling-based pillar strength estimation for an increased height of extraction. Arabian Journal of Geosciences. 2018;**10**(18):411. DOI: 10.1007/s12517-017-3179-6

[11] Sheorey PR. Pillar strength considering *in-situ* stresses. In: Information Circular (IC), 9315. United States: Department of the Interior, Bureau of Mines; 1992. pp. 122-127

[12] Kumar A, Waclawik P, Singh R, Ram S, Korbel J. Performance of a coal pillar at deeper cover: Field and simulation studies. International Journal of Rock Mechanics and Mining Sciences. 2019;**113**:322-332. DOI: 10.1016/j. ijrmms.2018.10.006

[13] Sheorey PR, Das MN, Barat D, Prasad RK, Singh B. Coal pillar strength estimation from failed and stable cases. International Journal of Rock Mechanics and Mining Science and Geomechanics Abstracts. 1987;**24**(6):347-355

[14] Kumar A, Singh AK, Kumar D, Ram S, Kumar R, Gautam A, et al.

*Developments Made for Mechanised Extraction of Locked-Up Coal Pillars in Indian Geomining… DOI: http://dx.doi.org/10.5772/intechopen.93636*

Caveability assessment of a hanging overlying massive Deccan trap and its effect on underground. Insights in Mining Science and Technology. 2019; **1**(3):50-60

**References**

00277-8

0860-7

[1] The Coal Mines Regulation. Published in The Gazette of India: Extraordinary issued by Ministry of Labour and Employment, Part- II-Section 3(i). 2017. pp. 160-280

*Mining Techniques - Past, Present and Future*

depillaring. In: Proceedings of 8th Asian

November 2019; Kolkata, India. MGMI;

[8] Kumar R, Mishra AK, Singh AK, Singh AK, Ram S, Singh R. Depillaring of total thickness of a thick coal seam in a single lift using cable bolts: A case study. International Journal of Mining Science and Technology. 2015;**25**(6):

[9] Kumar R, Singh AK, Mishra AK, Singh R. Underground mining of thick coal seams. International Journal of Mining Science and Technology. 2016;

[10] Kumar A, Kumar R, Singh AK, Ram S, Singh PK, Singh R. Numerical modelling-based pillar strength estimation for an increased height of extraction. Arabian Journal of Geosciences. 2018;**10**(18):411. DOI:

10.1007/s12517-017-3179-6

ijrmms.2018.10.006

[11] Sheorey PR. Pillar strength considering *in-situ* stresses. In:

Information Circular (IC), 9315. United States: Department of the Interior, Bureau of Mines; 1992. pp. 122-127

[12] Kumar A, Waclawik P, Singh R, Ram S, Korbel J. Performance of a coal pillar at deeper cover: Field and

[13] Sheorey PR, Das MN, Barat D, Prasad RK, Singh B. Coal pillar strength estimation from failed and stable cases. International Journal of Rock Mechanics and Mining Science and Geomechanics

Abstracts. 1987;**24**(6):347-355

[14] Kumar A, Singh AK, Kumar D, Ram S, Kumar R, Gautam A, et al.

simulation studies. International Journal of Rock Mechanics and Mining Sciences. 2019;**113**:322-332. DOI: 10.1016/j.

Mining Congress (AMC); 6-9

2019. pp. 529-538

885-896

**26**(2):223-233

[2] Singh AK, Kumar A, Kumar D, Singh R, Ram S, Kumar R, et al. Coal pillar extraction under weak roof. Mining, Metallurgy & Exploration. 2020. DOI: 10.1007/s42461-020-

[3] Kumar A, Kumar D, Verma AK, Singh AK, Ram S, Kumar R. Influence of overlying roof strata on rib design in mechanised depillaring. Journal of The Geological Society of India. 2018;**91**(3): 341-347. DOI: 10.1007/s12594-018-

[4] Singh R, Kumar A, Singh AK, Coggan J, Ram S. Rib/snook design in mechanised depillaring of rectangular/ square pillars. International Journal of Rock Mechanics and Mining Sciences. 2016;**84**:119-129. DOI: 10.1016/j.

[5] Ram S, Kumar D, Singh AK,

**93**:152-162. DOI: 10.1016/j. ijrmms.2017.01.013

[6] Kumar A, Kumar D, Singh AK, Ram S, Kumar R, Gautam A, et al. Roof sagging limit in an early warning system

[7] Kumar A, Kumar D, Singh AK, Ram S, Kumar R, Singh AK, et al. Strength estimation of irregular shaped heightened rib/snook for mechanised

**40**

International Journal of Rock Mechanics and Mining Sciences. 2019;**123**:104131. DOI: 10.1016/j.ijrmms.2019.104131

for safe coal pillar extraction.

Kumar A, Singh R. Field and numerical modelling studies for an efficient placement of roof bolts as breaker line support. International Journal of Rock Mechanics and Mining Sciences. 2017;

ijrmms.2016.02.008

[15] Sarkar SK, Singh B. Longwall Mining in India. Dhanbad: Sunanda Sarkar; 1985

**43**

mankind.

**Chapter 3**

**Abstract**

**1. Introduction**

Ecofriendly Hill Mining by

*Rama Dhar Dwivedi and Abhay Kumar Soni*

Mostly, hills are mined by 'Strip mining' i.e. removing the hills from top. This conventional approach destroys the landscape and defaces the beauty of the hill. Besides, a large amount of dust generated at source disturbs the villagers and nearby human settlements during the excavation operation or related activities. To eliminate this, and remove the 'out yard dumping of material', except at initial stage i.e. during developmental phase, if tunneling methods of civil construction work is applied, 'the conventional hill mining' can be turned into an eco-friendly hill mining with very little planning efforts. This chapter highlights the abovementioned aspects of 'hill mining' covering overviews about the 'hill mining by tunneling method'. In this technique, the extraction of mineral deposits is done by driving tunnels at the bottom (or other accessible higher level of the hills) and combining it with cross-cuts and adits, to protect the green cover and the serene hill environment. A case study of limestone mining in hilly Meghalaya region of India forms a

**Keywords:** hill mining, strip mining, tunneling in hills, mining of minerals in India

Hills are being mined since long, ever since man discovered the use of metals and valuable stones. The mineral resources (called mineral deposits) do exist both above ground level and below ground level. The hills have been mainly targeted because the winning of minerals above the ground is easier as compared to the mineral deposits found at depth. For instance, a broken hill lode in South Australia, one of the largest lead-zinc lode, ever discovered, is being mined for its mineral content in hills. Similarly, mining in hills is carried out for commercial minerals like iron ore (*Kudremukh, Karnataka*, India); bauxite (*Kollimalai hill deposits of Nilgiris* in Tamil Nadu India); base metal (*Arravallis in Rajasthan*, India); Magnesite of Indian Himalayas; useful stones such as granites, slates, marble, sandstone, etc. Thus, ubiquitous 'hill mining' was existing in the past, present and will continue to remain in future as well, wherever these deposits are made available by nature for

In the context of 'hill mining', two aspects matter significantly, and they are - 'scientific extraction' and 'environmental protection'. With judicious planning and serious efforts, *the conventional approach* of mineral extraction (mining) in hills can be turned into an eco-friendly hill mining. Fragile/serene hill environment can be

protected by adopting 'best practices' as applied in mining.

Tunneling Method

part of the description where its feasibility exists.

#### **Chapter 3**

## Ecofriendly Hill Mining by Tunneling Method

*Rama Dhar Dwivedi and Abhay Kumar Soni*

#### **Abstract**

Mostly, hills are mined by 'Strip mining' i.e. removing the hills from top. This conventional approach destroys the landscape and defaces the beauty of the hill. Besides, a large amount of dust generated at source disturbs the villagers and nearby human settlements during the excavation operation or related activities. To eliminate this, and remove the 'out yard dumping of material', except at initial stage i.e. during developmental phase, if tunneling methods of civil construction work is applied, 'the conventional hill mining' can be turned into an eco-friendly hill mining with very little planning efforts. This chapter highlights the abovementioned aspects of 'hill mining' covering overviews about the 'hill mining by tunneling method'. In this technique, the extraction of mineral deposits is done by driving tunnels at the bottom (or other accessible higher level of the hills) and combining it with cross-cuts and adits, to protect the green cover and the serene hill environment. A case study of limestone mining in hilly Meghalaya region of India forms a part of the description where its feasibility exists.

**Keywords:** hill mining, strip mining, tunneling in hills, mining of minerals in India

#### **1. Introduction**

Hills are being mined since long, ever since man discovered the use of metals and valuable stones. The mineral resources (called mineral deposits) do exist both above ground level and below ground level. The hills have been mainly targeted because the winning of minerals above the ground is easier as compared to the mineral deposits found at depth. For instance, a broken hill lode in South Australia, one of the largest lead-zinc lode, ever discovered, is being mined for its mineral content in hills. Similarly, mining in hills is carried out for commercial minerals like iron ore (*Kudremukh, Karnataka*, India); bauxite (*Kollimalai hill deposits of Nilgiris* in Tamil Nadu India); base metal (*Arravallis in Rajasthan*, India); Magnesite of Indian Himalayas; useful stones such as granites, slates, marble, sandstone, etc. Thus, ubiquitous 'hill mining' was existing in the past, present and will continue to remain in future as well, wherever these deposits are made available by nature for mankind.

In the context of 'hill mining', two aspects matter significantly, and they are - 'scientific extraction' and 'environmental protection'. With judicious planning and serious efforts, *the conventional approach* of mineral extraction (mining) in hills can be turned into an eco-friendly hill mining. Fragile/serene hill environment can be protected by adopting 'best practices' as applied in mining.

The characteristic features of hilly topography and the typical conditions encountered in such terrain have to be taken into account for achieving the desired results. Because favorable conditions do exist, a combination and integration of civil and mining engineering knowledge have been done and 'tunneling method' is evolved as an engineering field application. Various key aspects of hill mining covering overviews on the environment are also highlighted and described in the chapter. A selective case record of limestone mining in the Meghalaya state of India forms the part of the description for such type areas, the reason being its feasibility.

Conceptualization of tunneling method, though not new, came into our mind around the la*te* nineties *(≈ 1996 to 1998) when* limestone mining by underground methods was tried in an experimental adit in Himachal Pradesh, India**.** This site was located in the hilly Himalayas and the framed experimentation was found quite effective to protect the sensitive and fragile Himalayan environment [1]. In this way, integration of our knowledge about conventional 'underground method of mining 'and tunnel excavation work, prominent in hydel power projects of Himalaya, have to lead to the development of, *ecofriendly tunneling method*, considering the hill topography (or hill areas) as our concentration point.

#### **2. Hill mining by tunneling method**

Mostly, hills are excavated by 'stripping method', which consists of removing the top hill cover and moving downward (chopping down) in steps. When hills are mined for mineral extraction, the methodology of mining is termed as **'Strip Mining'**. This method is a conventional method and the extraction is carried out by construction of berms (or benches) to reach the deposit, and excavating mineral by digging either manually or mechanically. The conventional approach destroys the landscape and defaces beauty of the hill (**Figure 1**). Also, a large amount of dust generated at the source disturbs the surroundings, villagers and nearby human settlements during ongoing excavation operation or related ancillary activities.

#### **Figure 1.**

*Defacing of hills due to illegal quarrying is a typical sight in many hilly areas (severe environmental impacts to natural hill landforms).*

**45**

boreholes.

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

thus accrues to the cost of mining.

deposit/ore body and their properties.

ii.Overburden or rock cover above the orebody:

vertical in-situ stress, if any, at an underground place of workings.

i. Thickness and alignment:

iii. Rock joint properties:

encountered.

work, maybe the alternative that can be applied.

To eliminate and overcome this, 'tunneling methods', as used in civil construction

*Tunneling method* involves number of tunnels driven either in the country rocks and/or in the ore/mineral formation itself. The size of tunnels is chosen based on the thickness and compressive strength of the orebody and host rocks

It is well known that the economics of mineral extraction depends on the adopted mining method and its market value. Location, orientation, size and strength of ore deposit are the prime influential parameters to choose a mining method. However, nowadays environmental conditions are forcing the decision-makers to indulge in the activities which are ecofriendly or at least it should not harm the flora and fauna of the landscape. In this context, going underground without disturbing the natural surface features is appreciated for mining the minerals from the ground. In addition to this, the excavated *underground space* is preferred to be re-utilized either as a waste material refill or as a valuable space for miscellaneous purposes, to avoid subsidence at the ground surface above the mined-out area. Thus, rehabilitation of the excavated space is a value addition by public or industry. In such condition, the underground mined out areas need to be well supported so that these can stand for several coming years and

If the mineral deposit in a hill is found feasible for mining, it shall be mined

To extract mineral, location, thickness and alignment of mineral/orebody should be known as it influences the preparation of actual excavation plan (mining plan), to be implemented into practice. Overburden or rock cover should be known because it gives an idea about induced stresses around excavation built underground. Here, the size and diameter of the underground opening play an important role in the stability. Further, rock mass properties, information of water condition and physico-mechanical properties of rock mass decide the requirement of support

using 'tunneling method ', which would involve the following steps.

**A. Geological and geotechnical investigations for planning**

needed for the excavated area (i.e.tunnel walls) for the required life span.

Both, geological and geotechnical investigations help in the planning of mine and execution of various unit operations that lead to the extraction of mineral from the earth. These investigations reveal the following information about the mineral

Thickness indicates the volume of the orebody and determines the economy for mining activity and alignment or orientation is a deciding parameter for mining methodology. It is estimated with the help of core-log details obtained from various

This is the rock cover thickness above the orebody. It helps in the estimation of

Number and properties of rock joints together with the strength of rock mass helps to know its behavior when subjected to induced stresses during excavation

#### *Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Mining Techniques - Past, Present and Future*

topography (or hill areas) as our concentration point.

**2. Hill mining by tunneling method**

The characteristic features of hilly topography and the typical conditions encountered in such terrain have to be taken into account for achieving the desired results. Because favorable conditions do exist, a combination and integration of civil and mining engineering knowledge have been done and 'tunneling method' is evolved as an engineering field application. Various key aspects of hill mining covering overviews on the environment are also highlighted and described in the chapter. A selective case record of limestone mining in the Meghalaya state of India forms the part of the description for such type areas, the reason being its feasibility. Conceptualization of tunneling method, though not new, came into our mind around the la*te* nineties *(≈ 1996 to 1998) when* limestone mining by underground methods was tried in an experimental adit in Himachal Pradesh, India**.** This site was located in the hilly Himalayas and the framed experimentation was found quite effective to protect the sensitive and fragile Himalayan environment [1]. In this way, integration of our knowledge about conventional 'underground method of mining 'and tunnel excavation work, prominent in hydel power projects of Himalaya, have to lead to the development of, *ecofriendly tunneling method*, considering the hill

Mostly, hills are excavated by 'stripping method', which consists of removing the top hill cover and moving downward (chopping down) in steps. When hills are mined for mineral extraction, the methodology of mining is termed as **'Strip Mining'**. This method is a conventional method and the extraction is carried out by construction of berms (or benches) to reach the deposit, and excavating mineral by digging either manually or mechanically. The conventional approach destroys the landscape and defaces beauty of the hill (**Figure 1**). Also, a large amount of dust generated at the source disturbs the surroundings, villagers and nearby human settlements during ongoing excavation operation or related ancillary activities.

*Defacing of hills due to illegal quarrying is a typical sight in many hilly areas (severe environmental impacts to* 

**44**

**Figure 1.**

*natural hill landforms).*

To eliminate and overcome this, 'tunneling methods', as used in civil construction work, maybe the alternative that can be applied.

*Tunneling method* involves number of tunnels driven either in the country rocks and/or in the ore/mineral formation itself. The size of tunnels is chosen based on the thickness and compressive strength of the orebody and host rocks encountered.

It is well known that the economics of mineral extraction depends on the adopted mining method and its market value. Location, orientation, size and strength of ore deposit are the prime influential parameters to choose a mining method. However, nowadays environmental conditions are forcing the decision-makers to indulge in the activities which are ecofriendly or at least it should not harm the flora and fauna of the landscape. In this context, going underground without disturbing the natural surface features is appreciated for mining the minerals from the ground. In addition to this, the excavated *underground space* is preferred to be re-utilized either as a waste material refill or as a valuable space for miscellaneous purposes, to avoid subsidence at the ground surface above the mined-out area. Thus, rehabilitation of the excavated space is a value addition by public or industry. In such condition, the underground mined out areas need to be well supported so that these can stand for several coming years and thus accrues to the cost of mining.

If the mineral deposit in a hill is found feasible for mining, it shall be mined using 'tunneling method ', which would involve the following steps.

#### **A. Geological and geotechnical investigations for planning**

To extract mineral, location, thickness and alignment of mineral/orebody should be known as it influences the preparation of actual excavation plan (mining plan), to be implemented into practice. Overburden or rock cover should be known because it gives an idea about induced stresses around excavation built underground. Here, the size and diameter of the underground opening play an important role in the stability. Further, rock mass properties, information of water condition and physico-mechanical properties of rock mass decide the requirement of support needed for the excavated area (i.e.tunnel walls) for the required life span.

Both, geological and geotechnical investigations help in the planning of mine and execution of various unit operations that lead to the extraction of mineral from the earth. These investigations reveal the following information about the mineral deposit/ore body and their properties.

i. Thickness and alignment:

Thickness indicates the volume of the orebody and determines the economy for mining activity and alignment or orientation is a deciding parameter for mining methodology. It is estimated with the help of core-log details obtained from various boreholes.

ii.Overburden or rock cover above the orebody:

This is the rock cover thickness above the orebody. It helps in the estimation of vertical in-situ stress, if any, at an underground place of workings.

iii. Rock joint properties:

Number and properties of rock joints together with the strength of rock mass helps to know its behavior when subjected to induced stresses during excavation

activities below ground. Rock joints present also helps in knowing the water permeability of the strata.

iv.Location of the water table, if present:

Depth of water table provides information about water head to be considered while designing supports for roof or walls of the excavated area. In addition to this, it also gives an idea about the expected quantum of water inside the workings below ground.

v. Physico-mechanical properties:

Physical properties, like permeability (K) and specific gravity (γ) help the support designer in the estimation of the rate of water inrush and value of vertical in-situ stress respectively. Whereas, mechanical properties like Uniaxial compressive strength (σc), modulus of elasticity (E), Poisson's ratio (ν), cohesive strength (c), and angle of internal friction (ϕ) play a vital role in determining deformational behavior of rock mass (country rock and orebody) while excavation goes below ground during actual mining.

#### **B. Preparation of a mining plan.**

It includes preparation of geotechnical baseline reports, structural design report and drawings, for the approach roads, excavation sequence of tunnels and cross-cuts, applicable supports and drainage plan. As the reports and drawings are prepared based on geological and geotechnical data explored from the surface, the reports and drawings are revised when actual geology and rock types are encountered i.e. during going underground.

#### **C. Design of tunnels and cross-cuts.**

Size of tunnels is decided based on the rock mass quality, thickness of the orebody and rock cover. The rock mass is characterized and its quality is assessed using Barton's Q-system, rock mass rating (RMR) system or geological strength index (GSI) system. Rock mass with RMR value greater than or equal to 80 has high *standup time*. For example, 10 m of unsupported tunnel span can withstand up to about 70 months in a rock mass with RMR of 80 (Q = 55). Due to this reason, tunnel excavated in such quality rock mass does not require any artificial supports except spot bolting. On the other hand, the requirement of supports increases with a decrease in the quality of rock mass. Based on rock quality (Q-value), the quantum of supports required for tunnels of 5 m and 10 m diameter have been listed in **Table 1,** which have been obtained from the Barton's Q-chart as given in **Figure 2** [2].

Excavation support ratio (ESR) is the weightage assigned to the type of structure based on their importance. The more important structure is assigned with a lower value of ESR (**Table 2**). Value of ESR for temporary mining opening has been assigned as 3–5. Average ESR value (3) has been considered for calculation of supports in **Table 1** for the tunnels or cross-cuts, which are temporary and shall be backfilled after mining of the mineral/ore. On the other hand, the tunnels or crosscuts, which shall be retained as rehabilitated underground space are permanent and have been assigned with ESR value of 1.6.

This is significant to note that an arched crown of the tunnel distributes the induced stresses around the tunnel boundary in a better way. Required supports

**47**

**Figure 2.**

*Tunnel support chart based on Q-system [2].*

for tunnels of diameter 5 m and 10 m have been given in **Table 1** for construction in various quality of rock mass with Q-values greater than 0.4. Construction of tunnels in rock mass less than Q-value of 0.4 would attract the large quantum of supports and hence the mining cost may not be feasible for the ores of an average value. For the ores containing the high mineral value (silver, gold, zinc etc.), hill mining using tunnels would be economical even in the rock mass of very poor quality which

requires more stiff supports to stabilize the tunnel (s).

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

> **Tunnel span (D) =5 m Tunnel span (D) =10 m ESR = 1.6 ESR = 4 ESR = 1.6 ESR = 4 D/ESR Supports D/ESR Supports D/ESR Supports D/ESR Supports**

> > S = 1.5 m, Sc = 9 cm

> > S = 1.7 m, Sc = 8 cm

> > S = 2.1 m, Sc = 6 cm

> > > S = 2 m

2.5 Nil

2.5 Nil

2.5 Nil

2.5 Nil

0.4 3.125 Nil 1.25 Nil 6.25 L = 2.5 m,

1 3.125 Nil 1.25 Nil 6.25 L = 2.5 m,

4 3.125 Nil 1.25 Nil 6.25 L = 2.5 m,

10 3.125 Nil 1.25 Nil 6.25 L = 2.5 m,

40 3.125 Nil 1.25 Nil 6.25 Nil 2.5 Nil 50 3.125 Nil 1.25 Nil 6.25 Nil 2.5 Nil

*Notations: ESR-Excavation support ratio; L-Bolt length; S-spacing of bolt length; Sc-Reinforced shotcrete.*

*Requirement of supports according to rock mass quality and span or diameter of the tunnel.*

**Rock quality (Q )**

**Table 1.**


*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Notations: ESR-Excavation support ratio; L-Bolt length; S-spacing of bolt length; Sc-Reinforced shotcrete.*

#### **Table 1.**

*Mining Techniques - Past, Present and Future*

iv.Location of the water table, if present:

v. Physico-mechanical properties:

**B. Preparation of a mining plan.**

tered i.e. during going underground.

**C. Design of tunnels and cross-cuts.**

have been assigned with ESR value of 1.6.

ground during actual mining.

ability of the strata.

below ground.

activities below ground. Rock joints present also helps in knowing the water perme-

Depth of water table provides information about water head to be considered while designing supports for roof or walls of the excavated area. In addition to this, it also gives an idea about the expected quantum of water inside the workings

Physical properties, like permeability (K) and specific gravity (γ) help the support designer in the estimation of the rate of water inrush and value of vertical in-situ stress respectively. Whereas, mechanical properties like Uniaxial compressive strength (σc), modulus of elasticity (E), Poisson's ratio (ν), cohesive strength (c), and angle of internal friction (ϕ) play a vital role in determining deformational behavior of rock mass (country rock and orebody) while excavation goes below

It includes preparation of geotechnical baseline reports, structural design report and drawings, for the approach roads, excavation sequence of tunnels and cross-cuts, applicable supports and drainage plan. As the reports and drawings are prepared based on geological and geotechnical data explored from the surface, the reports and drawings are revised when actual geology and rock types are encoun-

Size of tunnels is decided based on the rock mass quality, thickness of the orebody and rock cover. The rock mass is characterized and its quality is assessed using Barton's Q-system, rock mass rating (RMR) system or geological strength index (GSI) system. Rock mass with RMR value greater than or equal to 80 has high *standup time*. For example, 10 m of unsupported tunnel span can withstand up to about 70 months in a rock mass with RMR of 80 (Q = 55). Due to this reason, tunnel excavated in such quality rock mass does not require any artificial supports except spot bolting. On the other hand, the requirement of supports increases with a decrease in the quality of rock mass. Based on rock quality (Q-value), the quantum of supports required for tunnels of 5 m and 10 m diameter have been listed in **Table 1,** which have been obtained from the Barton's Q-chart as given in

Excavation support ratio (ESR) is the weightage assigned to the type of structure based on their importance. The more important structure is assigned with a lower value of ESR (**Table 2**). Value of ESR for temporary mining opening has been assigned as 3–5. Average ESR value (3) has been considered for calculation of supports in **Table 1** for the tunnels or cross-cuts, which are temporary and shall be backfilled after mining of the mineral/ore. On the other hand, the tunnels or crosscuts, which shall be retained as rehabilitated underground space are permanent and

This is significant to note that an arched crown of the tunnel distributes the induced stresses around the tunnel boundary in a better way. Required supports

**46**

**Figure 2** [2].

*Requirement of supports according to rock mass quality and span or diameter of the tunnel.*

#### **Figure 2.** *Tunnel support chart based on Q-system [2].*

for tunnels of diameter 5 m and 10 m have been given in **Table 1** for construction in various quality of rock mass with Q-values greater than 0.4. Construction of tunnels in rock mass less than Q-value of 0.4 would attract the large quantum of supports and hence the mining cost may not be feasible for the ores of an average value. For the ores containing the high mineral value (silver, gold, zinc etc.), hill mining using tunnels would be economical even in the rock mass of very poor quality which requires more stiff supports to stabilize the tunnel (s).


#### **Table 2.**

*ESR values assigned to various type of structures [2].*

Tunnels or cross-cuts of 5 m diameter are very safe without any additional supports (except some spot bolting) for the suggested range of rock mass quality, i.e. Q ≥ 0.4 (**Table 1**). Rate of mineral/ore production shall be low using tunnels/crosscuts of 5 m diameter as compared to 10 m diameter tunnels because of deployment of smaller size machines in the former case. Similarly, mining with large tunnels of 10 m diameter shall also not require any additional supports, if excavation is carried out using controlled blasting technique i.e. causing minimum disturbance to the surrounding rock mass and the mined-out area is temporary and planned to be back-filled. Further, permanent openings of diameter 10 m created in a rock mass with quality index Q = 0.4–4 would need supports in form of 2.5 m long steel rock bolts at the spacing of 1.5–2.1 m with 6-9 cm steel fiber-reinforced shotcrete (SFRS). The same large openings in the rock mass with quality Q = 4–10 would need only rock 2.5 m long rock bolts at a spacing of 2 m as supports, whereas supports would not be required for the permanent 10 m diameter openings in a rock mass with Q > 10 (**Table 1**).

In mines, size of underground roadway i.e. roadway height and its dimension, as per the statute, is one point which needs due consideration while planning hill mining by tunneling method. In India, the dimensions of the pillars are regulated by Regulation 111 to 115 of Coal Mines Regulations (CMR), 2017 [4]. The regulation stipulates that the width of galleries shall not exceed 4.8 m and height of galleries shall not exceed 3 m. In this view, it is suggested to design the tunnels with width ≤ 4.8 m and height ≤ 3 m for coal deposits. Tunnels of larger dimensions may be designed for hill mining of non-coal minerals i.e. metallic minerals, which occur in narrow forms. However, smaller dimensions of excavation are always desirable from stability viewpoint because lager dimension gives rise to deformation and attracts requirement of stiffer supports. Thus, the smaller the opening better will be stability. If the value of the ore is high, the extraction by underground means, remain economical even after provision of stiffer support, mine planner can go for a larger dimension of underground openings.

For coal deposits having 30 x 30 m2 pillar dimension, the strength of pillar lies in the range of 5.4 MPa to 7.4 MPa at various depths. The pillar width shall be according

**49**

where,

**Table 3.**

ing Eq.2:

σs = strength of pillar (MPa).

*Width of square shape coal pillars at various depths.*

*W* = width of coal pillar (m). *h* = height of pillar (m) or gallery.

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

**For coal strength in a laboratory,** σ**c = 5.4 MPa**

For coal strength in the laboratory, σc = 7.4 MPa

σ**s (MPa) W/h** σ**<sup>p</sup>**

to the values given in **Table 3**. The gallery width and height are 4.8 m and 3 m respectively. Strength of pillar has been determined using the formula suggested by

*Note: All notations i.e. W, h, H,* σ*s and* σ*p has the same meaning as explained in Eq. 1 and 2 above.*

*s c* 0.64 0.36*<sup>W</sup>*

Stress on the pillar as shown in **Figure 3**, is computed according to the follow-

.

γ

*p*

σ

( ) ( )

*HW D W*

2

2

*h*

**(MPa)**

9.68 3.2 6.08 100 1.59 11.85 4.32 7.61 150 1.56 13.72 5.28 9.17 200 1.50 15.90 6.4 10.55 250 1.51 18.07 7.52 11.91 300 1.52 20.25 8.64 13.27 350 1.53 22.12 9.6 14.70 400 1.50 24.30 10.72 16.05 450 1.51 26.16 11.68 17.45 500 1.50

11.56 2.56 7.13 100 1.62 13.69 3.36 8.83 150 1.55 15.82 4.16 10.35 200 1.53 17.95 4.96 11.81 250 1.52 20.08 5.76 13.23 300 1.52 22.21 6.56 14.62 350 1.52 24.34 7.36 16.01 400 1.52 26.47 8.16 17.38 450 1.52 28.61 8.96 18.75 500 1.53

**H (m)**

**Factor of safety = (**σ**s***/* σ**p***)*

= + (1)

<sup>+</sup> <sup>=</sup> (2)

Bieniawski and Van [5] for square-shaped coal pillars (Eq.1).

σ σ

σc = unconfined compressive strength (MPa).

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Mining Techniques - Past, Present and Future*

*ESR values assigned to various type of structures [2].*

Tunnels or cross-cuts of 5 m diameter are very safe without any additional supports (except some spot bolting) for the suggested range of rock mass quality, i.e. Q ≥ 0.4 (**Table 1**). Rate of mineral/ore production shall be low using tunnels/crosscuts of 5 m diameter as compared to 10 m diameter tunnels because of deployment of smaller size machines in the former case. Similarly, mining with large tunnels of 10 m diameter shall also not require any additional supports, if excavation is carried out using controlled blasting technique i.e. causing minimum disturbance to the surrounding rock mass and the mined-out area is temporary and planned to be back-filled. Further, permanent openings of diameter 10 m created in a rock mass with quality index Q = 0.4–4 would need supports in form of 2.5 m long steel rock bolts at the spacing of 1.5–2.1 m with 6-9 cm steel fiber-reinforced shotcrete (SFRS). The same large openings in the rock mass with quality Q = 4–10 would need only rock 2.5 m long rock bolts at a spacing of 2 m as supports, whereas supports would not be required for the permanent 10 m diameter openings in a rock mass

**Category Type of structure ESR** A Temporary mine openings, etc. 3–5

> ii) rectangular/square section \* Depends on purpose and may be lower than given values.

penstocks), water supply tunnels, pilot tunnels, drifts and headings for large openings

etc.

tunnels, civil defense chambers, portals, intersections, etc.

facilitates, factories, etc.

100 years, or without access for maintenance.

C Permanent mine openings, water tunnels for hydropower (exclude high-pressure

D Minor road and railway tunnels, surge chambers, access tunnels, sewage tunnels,

E Powerhouses, storage rooms, water treatment plants, major road and railway

F Underground nuclear power stations, railways stations, sports and public

G Very important caverns and underground openings with a long lifetime,≈

2.5 2.0

1.6

1.3

1.0

0.8

0.5

B Vertical shafts\*: i) circular sections

In mines, size of underground roadway i.e. roadway height and its dimension, as per the statute, is one point which needs due consideration while planning hill mining by tunneling method. In India, the dimensions of the pillars are regulated by Regulation 111 to 115 of Coal Mines Regulations (CMR), 2017 [4]. The regulation stipulates that the width of galleries shall not exceed 4.8 m and height of galleries shall not exceed 3 m. In this view, it is suggested to design the tunnels with width ≤ 4.8 m and height ≤ 3 m for coal deposits. Tunnels of larger dimensions may be designed for hill mining of non-coal minerals i.e. metallic minerals, which occur in narrow forms. However, smaller dimensions of excavation are always desirable from stability viewpoint because lager dimension gives rise to deformation and attracts requirement of stiffer supports. Thus, the smaller the opening better will be stability. If the value of the ore is high, the extraction by underground means, remain economical even after provision of stiffer support, mine planner can go for a

range of 5.4 MPa to 7.4 MPa at various depths. The pillar width shall be according

pillar dimension, the strength of pillar lies in the

**48**

with Q > 10 (**Table 1**).

**Table 2.**

larger dimension of underground openings. For coal deposits having 30 x 30 m2


*Note: All notations i.e. W, h, H,* σ*s and* σ*p has the same meaning as explained in Eq. 1 and 2 above.*

#### **Table 3.**

*Width of square shape coal pillars at various depths.*

to the values given in **Table 3**. The gallery width and height are 4.8 m and 3 m respectively. Strength of pillar has been determined using the formula suggested by Bieniawski and Van [5] for square-shaped coal pillars (Eq.1).

$$
\sigma\_s = \sigma\_c \left[ 0.64 + 0.36 \frac{W}{h} \right] \tag{1}
$$

where,

σs = strength of pillar (MPa).

σc = unconfined compressive strength (MPa).

*W* = width of coal pillar (m).

*h* = height of pillar (m) or gallery.

Stress on the pillar as shown in **Figure 3**, is computed according to the following Eq.2:

$$
\sigma\_p = \frac{\gamma H.\left(W + D\right)^2}{\left(W\right)^2} \tag{2}
$$

**Figure 3.** *Plan view of a coal pillar.*

where,

σp = strength on the pillar (MPa). γ = unit weight of rock mass above the pillar in MPa/m. *H* = rock cover above the pillar. *W* = width of the pillar (m). *D* = width of the gallery (m).

#### **D. Limitations and other issues**

While dealing with hill mining by tunneling method, two important issues arise. Firstly, the 'shape of the underground openings' and secondly the mining methodology that includes both development and depillaring operation of mineral extraction. Due consideration should be given on both these points and its explanation has been given in the following paragraphs.

In general, tunnels are either D shaped (horseshoe shaped) or circular, having 'arched roof ' whereas underground mine galleries have nearly flat roofs. Tunnels with an arched roof are more stable and hence safer compared with the underground galleries. This is scientifically established that *flat roofs* having corners have more chances of failure due to higher stress concentration at the corners. The mine planner can select rectangular openings, if depillaring and backfilling are the parts of the mining plan and method of mining because backfilling, after the depillaring operation is over, takes care of stress concentration at the corners which are the likely point of initiation or propagation of failure/crushing in the underground openings. Furthermore, in case of depillaring with backfilling, additional land area (on the surface) is not required for rock/waste storage generated from excavation underground. Therefore, dump creation and its management are eliminated, thereby economizing the overall cost of mineral production. Waste rocks which are huge in quantity destroy the landscape of the surface area completely and cause water and land pollution. Saving of the landscape of the mining area is priceless in terms of environmental benefits. In this way, the suggested tunneling method, which is an improved form of *underground mining method* would be both economically viable and environmentally friendly. Following are some limitations of 'tunneling methods' which shall be mentioned here.

**51**

**Figure 4.**

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

• To make the 'tunneling method of mining' most feasible, the mined-out area shall be backfilled with rock waste, fly ash, sand or combination of more than one stowing material. Thus, 'depillaring with backfilling' is the best tunneling

• The method shall not be useful if entire rock cover is comprised of riverine

• According to a rough estimate the cost of underground mining is more compared to the open -cast or surface mining [1] hence, cost analysis is essential for 'tunneling method of mining'. If found appropriate, this limitation can be easily overcome, particularly for high value and strategic minerals (gold, uranium

When the tunneling method is practised, the value addition of the 'developed underground space' is suggestive. With such practices, the cost of production can be minimized and both revenues, as well as employment for locals, can be generated. Such value addition of the underground space/areas, if planned for the future, tunnels with an arched roof are advised. Research by the authors shows that the development roadways (areas developed during mine development, in particularly) has other civic uses too e.g. development as an underground storage space, place for

Approach roads are vital at hill sites. The paucity of land and constrained space in hills are some well-known problems of hill mining. For open surface mines, larger length of approach roads is needed, If the tunneling method is the choice of mineral winning, road length is reduced and dust hazard is kept contained. **Figures 4** and **5** show various approach roads to tunnels excavated in hills. The approach roads, only means of hill transportation, shall remain functional round the year to keep geared the mining activities in the hills and also for transportation of man, material and machinery. Their construction and design should be rugged enough as per the load they have to handle because heavy machinery of big size will often use the roads.

option, for safe exploitation of minerals by underground means.

material or soil having flowing tendency when destabilized.

ore, nickel ore, base metals i.e. Cu, lead, silver, zinc etc.).

a miscellaneous purpose, place of tourist extraction etc. [6].

*A view of the construction of approach road in the left for the tunnel shown on the right.*

**3. Construction of approach road**

#### *Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Mining Techniques - Past, Present and Future*

σp = strength on the pillar (MPa).

*H* = rock cover above the pillar. *W* = width of the pillar (m). *D* = width of the gallery (m).

**D. Limitations and other issues**

been given in the following paragraphs.

γ = unit weight of rock mass above the pillar in MPa/m.

While dealing with hill mining by tunneling method, two important issues arise. Firstly, the 'shape of the underground openings' and secondly the mining methodology that includes both development and depillaring operation of mineral extraction. Due consideration should be given on both these points and its explanation has

In general, tunnels are either D shaped (horseshoe shaped) or circular, having 'arched roof ' whereas underground mine galleries have nearly flat roofs. Tunnels with an arched roof are more stable and hence safer compared with the underground galleries. This is scientifically established that *flat roofs* having corners have more chances of failure due to higher stress concentration at the corners. The mine planner can select rectangular openings, if depillaring and backfilling are the parts of the mining plan and method of mining because backfilling, after the depillaring operation is over, takes care of stress concentration at the corners which are the likely point of initiation or propagation of failure/crushing in the underground openings. Furthermore, in case of depillaring with backfilling, additional land area (on the surface) is not required for rock/waste storage generated from excavation underground. Therefore, dump creation and its management are eliminated, thereby economizing the overall cost of mineral production. Waste rocks which are huge in quantity destroy the landscape of the surface area completely and cause water and land pollution. Saving of the landscape of the mining area is priceless in terms of environmental benefits. In this way, the suggested tunneling method, which is an improved form of *underground mining method* would be both economically viable and environmentally friendly. Following are some limitations of 'tunneling methods' which shall be

where,

*Plan view of a coal pillar.*

**Figure 3.**

**50**

mentioned here.


When the tunneling method is practised, the value addition of the 'developed underground space' is suggestive. With such practices, the cost of production can be minimized and both revenues, as well as employment for locals, can be generated. Such value addition of the underground space/areas, if planned for the future, tunnels with an arched roof are advised. Research by the authors shows that the development roadways (areas developed during mine development, in particularly) has other civic uses too e.g. development as an underground storage space, place for a miscellaneous purpose, place of tourist extraction etc. [6].

### **3. Construction of approach road**

Approach roads are vital at hill sites. The paucity of land and constrained space in hills are some well-known problems of hill mining. For open surface mines, larger length of approach roads is needed, If the tunneling method is the choice of mineral winning, road length is reduced and dust hazard is kept contained. **Figures 4** and **5** show various approach roads to tunnels excavated in hills. The approach roads, only means of hill transportation, shall remain functional round the year to keep geared the mining activities in the hills and also for transportation of man, material and machinery. Their construction and design should be rugged enough as per the load they have to handle because heavy machinery of big size will often use the roads.

**Figure 4.** *A view of the construction of approach road in the left for the tunnel shown on the right.*

**Figure 5.** *View of approaches to the tunnel constructed in the hill.*

#### **3.1 Layout of tunnels and cross-cuts for mining**

In a normal underground mine, the position of working face and its layout has close linkage as these facilitate the overall development of mine workings. Dimension and layout of tunnels and cross-cuts should be decided based on the thickness of the ore body. Thus, for the massive thickness of mineral bed, larger dimensions may be permitted. In case of metallic ore deposits which is found in narrow veins, lodes and pockets smaller dimensions suffice the purpose. For an orebody having a thickness in the range of 5 m or more, development of mine working shall be through tunnels and cross-cuts of diameter 'D' diameter (**Figure 6**).

The tunnels are constructed within the orebody or in host rocks. Construction of underground openings in host rocks is a non-productive exercise and shall be kept limited. This methodology starts giving production right from the beginning when underground excavations are made in mineral instead of host or country rocks. The tunnels are interconnected with cross-cuts of the same or different cross-section perpendicular to the tunnel direction/alignment at a fixed interval. Thus, pillars

**53**

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

**3.2 Productivity, risk and safety**

which should be attended scientifically.

excavated.

are formed which are extracted in the extraction phase of the mining operation. To get the mineral finally, these developed mine-workings are either fully or partially

The development of underground space, through tunneling and cross-cuts, for mining of minerals, has yet another dimension of multi-level mineralization in different horizons with host rocks in between, called 'parting'. All such levels, if not connected through tunnels from outside the hill, the dugout mineral or rocks can be poured down to the lower level and transportation underground can be done by gravity using shafts or chutes. Inter connectivity of levels at different points is required for the full development of the deposit which contains the mineral. If the mined-out area has to be backfilled then the pillar width should be reduced to a minimum with due consideration of roof stability. As such, the maximum quantity of ore should be dug out for mineral conservation purposes. At the decommissioning phase of 'eco-friendly hill mining by tunneling method', the underground space created during mining can create a value too and shall be maintained till the end. If done so, the underground space may be developed as a tourist place, underground

market and other utilities like hotels/shops in future which has value.

Thus, two aspects of the discussed method are quite apparent, firstly, 'clean mining and green environment' and secondly, 'value addition' after mining is over. Revenue generation and socio-economic gains are therefore well connected to the method at once the rehabilitation of the created underground space is sought.

In general, productivity is a measure of performance or output. It is a measure of how effectively the business targets of mining companies are being met [7]. In hill mining by underground approach, productivity is a ratio of input Vs output and implies how much mineral/ore is produced through various inputs. Obviously, hill mining, done by any method, has limited productivity and high risk. Its principal reasons are terrain condition. Another risks associated with the hill, particularly the Himalaya region, are the extreme weather conditions and environmental fragility,

*Tunneling methods of mineral extraction* has environmental and safety advantages

*Deformation monitoring of excavated underground stretches:* For safe underground working, the stability of the tunnel/cross-cuts is highly recommended to monitor so that counter measures can be taken in time to strengthen the rock mass around the excavated opening i.e. tunnel periphery wherever needed. For this, bi reflex targets are fixed at various cross-sections, especially near the cross-cuts because there are large spans of excavated space at such places, which need special care. After all, large excavations attract high induced stresses around the boundary of the openings. The targets are suggested to fix as given in **Figures 7** and **8**. One target at each TP1 (crown), TP2 & TP3 at the springing level and TP4 & TP5 at the upper bottom. Frequency of such measurement depends on the trend of change in the radial deformation. If deformation shows an increasing trend, the frequency of

over conventional mining. Safety in mines and mining industry (from accident angle) is prime and has to be maintained and accrued through constant efforts. At ground level, the safety can be enhanced or dealt effectively with knowledge of "Safety Management and Safety Engineering", as they are the modern and newly emerged tools to achieve the road to zero harm [8]. Undoubtedly, safety is a major concern for lofty hills and for this mining professionals are required to keep an eye on the stability of underground openings and slopes near the underground entry points i.e. portals. For this, scientific tools of numerical modeling, field measure-

ment etc. pave the way as described in the following two paragraphs.

**Figure 6.** *Layout of tunnels for hill mining.*

#### *Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Mining Techniques - Past, Present and Future*

**3.1 Layout of tunnels and cross-cuts for mining**

*View of approaches to the tunnel constructed in the hill.*

**Figure 5.**

In a normal underground mine, the position of working face and its layout has close linkage as these facilitate the overall development of mine workings. Dimension and layout of tunnels and cross-cuts should be decided based on the thickness of the ore body. Thus, for the massive thickness of mineral bed, larger dimensions may be permitted. In case of metallic ore deposits which is found in narrow veins, lodes and pockets smaller dimensions suffice the purpose. For an orebody having a thickness in the range of 5 m or more, development of mine working shall be through tunnels and cross-cuts of diameter 'D' diameter (**Figure 6**).

The tunnels are constructed within the orebody or in host rocks. Construction of underground openings in host rocks is a non-productive exercise and shall be kept limited. This methodology starts giving production right from the beginning when underground excavations are made in mineral instead of host or country rocks. The tunnels are interconnected with cross-cuts of the same or different cross-section perpendicular to the tunnel direction/alignment at a fixed interval. Thus, pillars

**52**

**Figure 6.**

*Layout of tunnels for hill mining.*

are formed which are extracted in the extraction phase of the mining operation. To get the mineral finally, these developed mine-workings are either fully or partially excavated.

The development of underground space, through tunneling and cross-cuts, for mining of minerals, has yet another dimension of multi-level mineralization in different horizons with host rocks in between, called 'parting'. All such levels, if not connected through tunnels from outside the hill, the dugout mineral or rocks can be poured down to the lower level and transportation underground can be done by gravity using shafts or chutes. Inter connectivity of levels at different points is required for the full development of the deposit which contains the mineral. If the mined-out area has to be backfilled then the pillar width should be reduced to a minimum with due consideration of roof stability. As such, the maximum quantity of ore should be dug out for mineral conservation purposes. At the decommissioning phase of 'eco-friendly hill mining by tunneling method', the underground space created during mining can create a value too and shall be maintained till the end. If done so, the underground space may be developed as a tourist place, underground market and other utilities like hotels/shops in future which has value.

Thus, two aspects of the discussed method are quite apparent, firstly, 'clean mining and green environment' and secondly, 'value addition' after mining is over. Revenue generation and socio-economic gains are therefore well connected to the method at once the rehabilitation of the created underground space is sought.

#### **3.2 Productivity, risk and safety**

In general, productivity is a measure of performance or output. It is a measure of how effectively the business targets of mining companies are being met [7]. In hill mining by underground approach, productivity is a ratio of input Vs output and implies how much mineral/ore is produced through various inputs. Obviously, hill mining, done by any method, has limited productivity and high risk. Its principal reasons are terrain condition. Another risks associated with the hill, particularly the Himalaya region, are the extreme weather conditions and environmental fragility, which should be attended scientifically.

*Tunneling methods of mineral extraction* has environmental and safety advantages over conventional mining. Safety in mines and mining industry (from accident angle) is prime and has to be maintained and accrued through constant efforts. At ground level, the safety can be enhanced or dealt effectively with knowledge of "Safety Management and Safety Engineering", as they are the modern and newly emerged tools to achieve the road to zero harm [8]. Undoubtedly, safety is a major concern for lofty hills and for this mining professionals are required to keep an eye on the stability of underground openings and slopes near the underground entry points i.e. portals. For this, scientific tools of numerical modeling, field measurement etc. pave the way as described in the following two paragraphs.

*Deformation monitoring of excavated underground stretches:* For safe underground working, the stability of the tunnel/cross-cuts is highly recommended to monitor so that counter measures can be taken in time to strengthen the rock mass around the excavated opening i.e. tunnel periphery wherever needed. For this, bi reflex targets are fixed at various cross-sections, especially near the cross-cuts because there are large spans of excavated space at such places, which need special care. After all, large excavations attract high induced stresses around the boundary of the openings. The targets are suggested to fix as given in **Figures 7** and **8**. One target at each TP1 (crown), TP2 & TP3 at the springing level and TP4 & TP5 at the upper bottom.

Frequency of such measurement depends on the trend of change in the radial deformation. If deformation shows an increasing trend, the frequency of

#### **Figure 7.**

*Position of bi-reflex targets required to fix for monitoring radial tunnel deformation.*

**Figure 8.** *Bi-reflex targets fixed to monitor radial tunnel deformation.*

**55**

**Figure 10.**

*Bireflex targets fixed at a tunnel portal to monitor the movement of the slope.*

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

80% of the allowable limit as per the design.

measures.

tor the water head.

mining' [1].

measurement needs to be increased. The readings obtained from such monitoring should be religiously analyzed so that action can be taken in advance before any untoward incidence (accident) takes place. **Figure 9** shows tunnel deformation in vertical, horizontal and longitudinal directions at TP1, TP2, TP3, TP4 and TP5 target points of a tunnel section. Alarming deformation level should be fixed at

**Slope monitoring near facade/tunnel portals:** The purpose of a slope monitoring is to plan and maintain safe operating practises for the protection of personnel, equipment, and facilities. It provides warning of instability, so that action can be taken to minimize the impact of slope displacement and analyze the slope failure mechanism. The crucial geotechnical information provides help in designing the appropriate corrective measures [9]. Sufficient and suitable monitoring must be done to detect instability at an early, non-critical stage, to initiate the safety

Opening of the mine i.e. portals of the tunnels is of prime importance as these serve as escape routes. Therefore, it is highly recommended to keep them intact and stable throughout the life of their existence and for a longer period, particularly when the mined-out areas have to be utilized for civic purposes in future. From this viewpoint, the portals are strongly supported with sufficient stretches (up to 15 m from the portals) and support density (1.25 times). To monitor the slope stability, bi-reflex targets are fixed at portal slopes as shown in **Figure 10**. Inclinometer and slope monitoring electronic gazettes such as 'terrestrial laser scanner (TSL)' and 'slope stability radar' (SSR) are some available equipment that may be used to assess the movement of hill slopes [10]. Depending on the requirement and feasibility on cost economics basis, they may be deployed. Piezometers can be installed to moni-

Precisely, the tunneling method for hills is an eco-friendly method that adopts similar basic principles as that of 'underground mining' in general and follows similar safety routes. To get a speedy and fast return on investment, the tunneling method of mining is best suited for the high-value minerals however, coal and other low-value minerals namely limestone, dolomite etc. can also be mined by this method taking into account the cost–benefit analysis. To make the method more cost-effective for mineral extraction, another dimension that may be added to this method is the 'eco-friendly transportation in hills' [11] and 'best practice

**Figure 9.** *Tunnel deformation recorded at all bi reflex targets of a tunnel section.*

#### *Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

*Mining Techniques - Past, Present and Future*

**54**

**Figure 9.**

**Figure 8.**

**Figure 7.**

*Bi-reflex targets fixed to monitor radial tunnel deformation.*

*Position of bi-reflex targets required to fix for monitoring radial tunnel deformation.*

*Tunnel deformation recorded at all bi reflex targets of a tunnel section.*

measurement needs to be increased. The readings obtained from such monitoring should be religiously analyzed so that action can be taken in advance before any untoward incidence (accident) takes place. **Figure 9** shows tunnel deformation in vertical, horizontal and longitudinal directions at TP1, TP2, TP3, TP4 and TP5 target points of a tunnel section. Alarming deformation level should be fixed at 80% of the allowable limit as per the design.

**Slope monitoring near facade/tunnel portals:** The purpose of a slope monitoring is to plan and maintain safe operating practises for the protection of personnel, equipment, and facilities. It provides warning of instability, so that action can be taken to minimize the impact of slope displacement and analyze the slope failure mechanism. The crucial geotechnical information provides help in designing the appropriate corrective measures [9]. Sufficient and suitable monitoring must be done to detect instability at an early, non-critical stage, to initiate the safety measures.

Opening of the mine i.e. portals of the tunnels is of prime importance as these serve as escape routes. Therefore, it is highly recommended to keep them intact and stable throughout the life of their existence and for a longer period, particularly when the mined-out areas have to be utilized for civic purposes in future. From this viewpoint, the portals are strongly supported with sufficient stretches (up to 15 m from the portals) and support density (1.25 times). To monitor the slope stability, bi-reflex targets are fixed at portal slopes as shown in **Figure 10**. Inclinometer and slope monitoring electronic gazettes such as 'terrestrial laser scanner (TSL)' and 'slope stability radar' (SSR) are some available equipment that may be used to assess the movement of hill slopes [10]. Depending on the requirement and feasibility on cost economics basis, they may be deployed. Piezometers can be installed to monitor the water head.

Precisely, the tunneling method for hills is an eco-friendly method that adopts similar basic principles as that of 'underground mining' in general and follows similar safety routes. To get a speedy and fast return on investment, the tunneling method of mining is best suited for the high-value minerals however, coal and other low-value minerals namely limestone, dolomite etc. can also be mined by this method taking into account the cost–benefit analysis. To make the method more cost-effective for mineral extraction, another dimension that may be added to this method is the 'eco-friendly transportation in hills' [11] and 'best practice mining' [1].

**Figure 10.** *Bireflex targets fixed at a tunnel portal to monitor the movement of the slope.*

#### **4. Case study: limestone mining in Meghalaya**

Meghalaya, a high rain intensity state of India, in the North-Eastern part is mostly a hilly state (West, South and East Garo Hills; West and East Khasi Hills and Jaintia Hills) where sky seldom remains free of clouds. Meghalaya is rich in minerals and blessed with about 9% of the total limestone reserve of India [12]. The hills containing limestone minerals are being mined by open cast mining method in Meghalaya. Conventional 'Strip mining' is the method adopted in hill mining at Meghalaya.

Geologically, limestone in Meghalaya falls under the rocks formations namely Cretaceous-Tertiary sedimentary rock, which is further divided into three groups i.e., the Khasi group, the Jaintia Group and the Garo group. The Jaintia Group is further sub-divided into three formations, which include the *Longpar (lower), the Shella (middle)* and the *Kopili (upper)* formations.

The limestone deposited in Jaintia Hills, possesses limestone with alternating bands of sandstone. However, the limestone deposit in Cherrapunjee area of Meghalaya consists of limestone layers in the upper part of hills and dolomite in the lower portion. The limestone rocks found in Meghalaya belong to the Shella formations of the Jaintia Group of Cretaceous-Tertiary sedimentary rocks of Eocene geological age [3, 13].

As described above, in hill districts of Meghalaya, limestone is being extracted by open cast method of mining at both large scale and small scale levels. Jaintia Hills is being extracted in large scale for cement, whereas East Khasi hills are being extracted in small and large scale for manufacturing of quick lime, edible lime and cement. Most of the mines are owned by small private entrepreneurs. Some of the landowners are organized, and some make use of crude methods and adopt unscientific practices of mining on an individual basis to extract limestone. The captive mines of the cement industries are efficient, being mechanized, make use of heavy machinery for excavation. On the other hand, extraction by individual landowners is manual or semi-mechanical only and thus slow.

It is noticed and revealed periodically, that the local environment around the mines or in mining regions has been affected by creating hullabaloo. Engaged mining companies of the concerned area of the state faces its consequences both financially and socially (**Figure 11**). In general, extraction of limestone involves mechanical removal of overburden (using bulldozers), drilling of the blast holes, blasting of rocks (shattering), sizing, loading and then finally transportation of limestone to the consumer or industry cement plants.

In many hilly areas of Meghalaya, quarrying, for limestone, building stone/ material such as slate, granite, clay etc., is a typical sight. Most of them are unscientific and cause disastrous and irreversible changes to natural habitats. At the

**57**

**Author details**

Rama Dhar Dwivedi1

(Uttarakhand), India

(Maharashtra), India

and Abhay Kumar Soni2

of mineral deposits in hills irrespective of the scale of mining.

\*Address all correspondence to: abhayksoni@gmail.com

provided the original work is properly cited.

1 CSIR-Central Institute of Mining and Fuel Research (CIMFR), Roorkee,

2 CSIR-Central Institute of Mining and Fuel Research (CIMFR), Nagpur,

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*

*Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

approach (tunneling).

**5. Conclusions**

developmental phase, to reach the deposit, the mineral winning process shall be through driving of tunnel and approaching underground instead of the surface. With adequate planning, 'the tunneling method' can be implemented into practices at Meghalaya as its tremendous feasibility exist. In this way, agricultural land and the landscape, nearby rivers and other water bodies, are not polluted. Air, water and land environment of the area can be protected with underground hill mining

Our experience of working in Indian mines and the analysis described in this technical communication concludes that 'the conventional hill mining can be turned into eco-friendly mining with small efforts, according to the hill topography, when the tunneling method is selected for implementation into practice. Many hill areas, including The Himalayas, will be the direct beneficiary and by doing so land degradation could be reduced to a minimum. The ill-effects of surface mining e.g. possibility of deforestation/denudation of forest, creation of scars on hill slopes (defacing) due to dumping on slopes, destabilization of natural hill slopes, landslides (destabilization) of hills, water pollution and disturbance to natural drainage pattern of the hills are either eliminated or curbed substantially. In this way, mining and environment can go hand-in-hand and the greenery of a hill and the surrounded environment is preserved. The less disturbed land surface, on one hand, protect the serene hill environment and on other hand allows the production

**Figure 11.** *View of various opencast mines in Meghalaya.*

#### *Ecofriendly Hill Mining by Tunneling Method DOI: http://dx.doi.org/10.5772/intechopen.95918*

developmental phase, to reach the deposit, the mineral winning process shall be through driving of tunnel and approaching underground instead of the surface.

With adequate planning, 'the tunneling method' can be implemented into practices at Meghalaya as its tremendous feasibility exist. In this way, agricultural land and the landscape, nearby rivers and other water bodies, are not polluted. Air, water and land environment of the area can be protected with underground hill mining approach (tunneling).

#### **5. Conclusions**

*Mining Techniques - Past, Present and Future*

Meghalaya.

geological age [3, 13].

**4. Case study: limestone mining in Meghalaya**

*Shella (middle)* and the *Kopili (upper)* formations.

is manual or semi-mechanical only and thus slow.

limestone to the consumer or industry cement plants.

Meghalaya, a high rain intensity state of India, in the North-Eastern part is mostly a hilly state (West, South and East Garo Hills; West and East Khasi Hills and Jaintia Hills) where sky seldom remains free of clouds. Meghalaya is rich in minerals and blessed with about 9% of the total limestone reserve of India [12]. The hills containing limestone minerals are being mined by open cast mining method in Meghalaya. Conventional 'Strip mining' is the method adopted in hill mining at

Geologically, limestone in Meghalaya falls under the rocks formations namely Cretaceous-Tertiary sedimentary rock, which is further divided into three groups i.e., the Khasi group, the Jaintia Group and the Garo group. The Jaintia Group is further sub-divided into three formations, which include the *Longpar (lower), the* 

The limestone deposited in Jaintia Hills, possesses limestone with alternating bands of sandstone. However, the limestone deposit in Cherrapunjee area of Meghalaya consists of limestone layers in the upper part of hills and dolomite in the lower portion. The limestone rocks found in Meghalaya belong to the Shella formations of the Jaintia Group of Cretaceous-Tertiary sedimentary rocks of Eocene

As described above, in hill districts of Meghalaya, limestone is being extracted by open cast method of mining at both large scale and small scale levels. Jaintia Hills is being extracted in large scale for cement, whereas East Khasi hills are being extracted in small and large scale for manufacturing of quick lime, edible lime and cement. Most of the mines are owned by small private entrepreneurs. Some of the landowners are organized, and some make use of crude methods and adopt unscientific practices of mining on an individual basis to extract limestone. The captive mines of the cement industries are efficient, being mechanized, make use of heavy machinery for excavation. On the other hand, extraction by individual landowners

It is noticed and revealed periodically, that the local environment around the mines or in mining regions has been affected by creating hullabaloo. Engaged mining companies of the concerned area of the state faces its consequences both financially and socially (**Figure 11**). In general, extraction of limestone involves mechanical removal of overburden (using bulldozers), drilling of the blast holes, blasting of rocks (shattering), sizing, loading and then finally transportation of

In many hilly areas of Meghalaya, quarrying, for limestone, building stone/ material such as slate, granite, clay etc., is a typical sight. Most of them are unscientific and cause disastrous and irreversible changes to natural habitats. At the

**56**

**Figure 11.**

*View of various opencast mines in Meghalaya.*

Our experience of working in Indian mines and the analysis described in this technical communication concludes that 'the conventional hill mining can be turned into eco-friendly mining with small efforts, according to the hill topography, when the tunneling method is selected for implementation into practice. Many hill areas, including The Himalayas, will be the direct beneficiary and by doing so land degradation could be reduced to a minimum. The ill-effects of surface mining e.g. possibility of deforestation/denudation of forest, creation of scars on hill slopes (defacing) due to dumping on slopes, destabilization of natural hill slopes, landslides (destabilization) of hills, water pollution and disturbance to natural drainage pattern of the hills are either eliminated or curbed substantially. In this way, mining and environment can go hand-in-hand and the greenery of a hill and the surrounded environment is preserved. The less disturbed land surface, on one hand, protect the serene hill environment and on other hand allows the production of mineral deposits in hills irrespective of the scale of mining.

#### **Author details**

Rama Dhar Dwivedi1 and Abhay Kumar Soni<sup>2</sup> \*

1 CSIR-Central Institute of Mining and Fuel Research (CIMFR), Roorkee, (Uttarakhand), India

2 CSIR-Central Institute of Mining and Fuel Research (CIMFR), Nagpur, (Maharashtra), India

\*Address all correspondence to: abhayksoni@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Soni A.K. (2017), Mining in the Himalayas - An Integrated Strategy, Book Published by CRC Press / Taylor & Francis, p. 225 (ISBN - 9781498762342).

[2] NGI (2015). Using the Q-system: Rock mass classification and support design, Norwegian Geotechnical Institute (NGI) Publication, 54p.

[3] DMR (2016), Directorate of Mineral Resources (DMR) Profile, Government of Meghalaya (http://megdmg.gov.in/), Shillong, Meghalaya.

[4] GOI (2017), Coal Mines Regulations, 2017, Government of India (GOI), Amended and modified from Coal Mines Regulation (CMR), 1957(from the web; last accessed 0n 17/09/2020).

[5] Bieniawski ZT, Van HWL (1975). The significance of in situ tests on large rock specimens. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 12(4): 101-113.

[6] Soni A.K., (1995), Environmental Study of a Limestone Mining in the Himalayas, Journal of Mining Research, Vol. 3, Nos. 3 &4, January–March, pp.1-8.

[7] Jairo Ndhlovuand Peter R K Chileshe (2020), Global Mine Productivity Issues: A Review, Int. J. of Engineering Research & Technology (IJERT), Vol. 9 Issue 05, May ( ISSN: 2278-0181; http:// www.ijert.org), pp. 319-329.

[8] Soni A.K. and Suman Kiran (2012), The Road to Zero Harm: Safety Management and Safety Engineering in Context to Underground Mines, Workshop on Safety Management in Mines. Nagpur, pp. 01-10.

[9] Call R.D., J.P. Savely (1990). Openpit rock mechanics. Surface Mining, 2nd Edition. Society for Mining, Metallurgy and Exploration, Inc., pp. 860-882. B.A. Kennedy ed.

[10] Prakash Amar, Kumar A., Singh K. B. (2016). Highwall mining: A critical appraisal, MineTech, Vol. 36 No. 3, pp. 17-30.

[11] Soni A.K. (1999), Environmentally - Friendly Transportation of Limestone for Cement Production, International Journal of Bulk Solid Handling - Germany, ISSN: 01739980 Vol.19. N0.3, July–September, pp. 329-336.

[12] Lamare R. E., Singh O. P. (2016). Limestone mining and its environmental implications in Meghalaya, India. ENVIS Bulletin Himalayan Ecology, 24:87-100.

[13] Sarma S. (2003). Meghalaya: The Land and Forest - A Remote Sensing Based Study, Geophil Publishing House, Guwahati, India, 5-16.

**59**

**Chapter 4**

**Abstract**

tion close to the natural soil.

**1. Why this study is important?**

question we have just put forward.

edaphic mesofauna

Reclamation of Soils Degraded by

*Luiz Fernando Spinelli Pinto, Lizete Stumpf, Pablo Miguel,* 

The largest Brazilian coal mine, called Candiota mine, is located in South Brazil, with an estimated reserve about 1.2 billion tons. Since late 2003, an experiment located at a reclaimed site in a coal mining area was conducted, in which a research group from the Federal University of Pelotas has been conducting a long-term experiment on soil quality with different plants species, such as *Hemarthria altissima*, *Paspalum notatum* cv. Pensacola, *Cynodon dactylon* cv. Tifton, and *Urochloa brizantha*. After 8.6 years of revegetation, soil samples at 0.20 depth were collected in minesoil and natural soil to determine physical attributes, and the organic carbon content. After 10.9 years of revegetation, soil samples at 0.10 m depth were collected to determine the biological attributes. According to the research results, it can be seen that the recovery of minesoil was more effective after 8.6 years of revegetation only in the physical condition up to 0.10 m depth. However, all soil physical attributes and organic matter content are still below the levels observed in the natural soil. The biological attributes after 10.9 years of revegetation have not yet been sufficient to restore a mites and springtails popula-

**Keywords:** minesoil, revegetation, physical attributes, organic matter content,

"Soil" is borne as a result of lengthy natural processes over thousands of years; hence, it is a valuable nonrenewable commodity. It is a basic environment needed for vegetation growth on land, be it a mined land or other. In case of soils degraded by surface coal mining, one should not bear in mind it would be a simple task to bring back degraded/mined soil to its near original configuration so that it would become naturally capable to sustainably support vegetation. With this aim, we carried out our study and here lies the "time period to bring back the degraded minesoil to close to natural soil condition," which is an extremely important requirement for surface coal mining successful closure. This research study has put stress on the long-time scientific evaluation of coal mine soil degraded by the excavation operation, i.e., mining (for more than 16 years). Though maintaining such experiment requires lot of efforts and resources, we think it is a necessary tool to analyze the

*Leonir Aldrighi Dutra Junior, Jeferson Diego Leidemer,* 

*Lucas da Silva Barbosa and Mauricio Silva e Oliveira*

Surface Coal Mining

#### **Chapter 4**

## Reclamation of Soils Degraded by Surface Coal Mining

*Luiz Fernando Spinelli Pinto, Lizete Stumpf, Pablo Miguel, Leonir Aldrighi Dutra Junior, Jeferson Diego Leidemer, Lucas da Silva Barbosa and Mauricio Silva e Oliveira*

#### **Abstract**

The largest Brazilian coal mine, called Candiota mine, is located in South Brazil, with an estimated reserve about 1.2 billion tons. Since late 2003, an experiment located at a reclaimed site in a coal mining area was conducted, in which a research group from the Federal University of Pelotas has been conducting a long-term experiment on soil quality with different plants species, such as *Hemarthria altissima*, *Paspalum notatum* cv. Pensacola, *Cynodon dactylon* cv. Tifton, and *Urochloa brizantha*. After 8.6 years of revegetation, soil samples at 0.20 depth were collected in minesoil and natural soil to determine physical attributes, and the organic carbon content. After 10.9 years of revegetation, soil samples at 0.10 m depth were collected to determine the biological attributes. According to the research results, it can be seen that the recovery of minesoil was more effective after 8.6 years of revegetation only in the physical condition up to 0.10 m depth. However, all soil physical attributes and organic matter content are still below the levels observed in the natural soil. The biological attributes after 10.9 years of revegetation have not yet been sufficient to restore a mites and springtails population close to the natural soil.

**Keywords:** minesoil, revegetation, physical attributes, organic matter content, edaphic mesofauna

#### **1. Why this study is important?**

"Soil" is borne as a result of lengthy natural processes over thousands of years; hence, it is a valuable nonrenewable commodity. It is a basic environment needed for vegetation growth on land, be it a mined land or other. In case of soils degraded by surface coal mining, one should not bear in mind it would be a simple task to bring back degraded/mined soil to its near original configuration so that it would become naturally capable to sustainably support vegetation. With this aim, we carried out our study and here lies the "time period to bring back the degraded minesoil to close to natural soil condition," which is an extremely important requirement for surface coal mining successful closure. This research study has put stress on the long-time scientific evaluation of coal mine soil degraded by the excavation operation, i.e., mining (for more than 16 years). Though maintaining such experiment requires lot of efforts and resources, we think it is a necessary tool to analyze the question we have just put forward.

**58**

Kennedy ed.

pp.1-8.

*Mining Techniques - Past, Present and Future*

[1] Soni A.K. (2017), Mining in the Himalayas - An Integrated Strategy, Book Published by CRC Press / Taylor & Francis, p. 225 (ISBN - 9781498762342).

**References**

[10] Prakash Amar, Kumar A., Singh K. B. (2016). Highwall mining: A critical appraisal, MineTech, Vol. 36 No. 3, pp.

[11] Soni A.K. (1999), Environmentally - Friendly Transportation of Limestone for Cement Production, International Journal of Bulk Solid Handling - Germany, ISSN: 01739980 Vol.19. N0.3,

July–September, pp. 329-336.

Guwahati, India, 5-16.

[12] Lamare R. E., Singh O. P. (2016). Limestone mining and its environmental implications in Meghalaya, India. ENVIS Bulletin Himalayan Ecology, 24:87-100.

[13] Sarma S. (2003). Meghalaya: The Land and Forest - A Remote Sensing Based Study, Geophil Publishing House,

17-30.

[2] NGI (2015). Using the Q-system: Rock mass classification and support design, Norwegian Geotechnical Institute (NGI) Publication, 54p.

[3] DMR (2016), Directorate of Mineral Resources (DMR) Profile, Government of Meghalaya (http://megdmg.gov.in/),

[4] GOI (2017), Coal Mines Regulations, 2017, Government of India (GOI), Amended and modified from Coal Mines Regulation (CMR), 1957(from the web; last accessed 0n 17/09/2020).

[5] Bieniawski ZT, Van HWL (1975). The significance of in situ tests on large rock specimens. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 12(4): 101-113.

[6] Soni A.K., (1995), Environmental Study of a Limestone Mining in the Himalayas, Journal of Mining Research, Vol. 3, Nos. 3 &4, January–March,

[7] Jairo Ndhlovuand Peter R K Chileshe (2020), Global Mine Productivity Issues: A Review, Int. J. of Engineering Research & Technology (IJERT), Vol. 9 Issue 05, May ( ISSN: 2278-0181; http://

[8] Soni A.K. and Suman Kiran (2012),

[9] Call R.D., J.P. Savely (1990). Openpit rock mechanics. Surface Mining, 2nd Edition. Society for Mining, Metallurgy and Exploration, Inc., pp. 860-882. B.A.

www.ijert.org), pp. 319-329.

The Road to Zero Harm: Safety Management and Safety Engineering in Context to Underground Mines, Workshop on Safety Management in

Mines. Nagpur, pp. 01-10.

Shillong, Meghalaya.

Our study was done in a randomized block design field experiment, sampling the same soil over the time, and comparing the soil properties with the natural soil, what makes the data obtained more scientifically reliable and meaningful. We, as authors, have tried to make this idea more clear in our writing; it is well known and obvious that the soils properties once covered with vegetation will tend to improve over time. Nevertheless, this does not necessarily happen, and sometimes, many sites show signs of degradation and even erosions problems after many years of reclamation, needing re-intervention.

Therefore, the main difference between our study and other similar studies is that of experimental control. Most studies deal with sampling of mining sites, with different ages, but without experimental control. It is also important to do research on soil reclamation techniques and procedures focusing on improving minesoil quality, ensuring the return of a productive soil according to the planned use.

#### **2. Soils formed in surface coal mining**

Coal remains a major fuel in global energy systems, accounting for almost 40% of electricity generation, and over the next 5 years, the global coal demand is forecasted to remain stable, supported by the resilient Chinese market, which accounts for half of the global consumption [1]. World coal reserves have a volume of approximately 860 billion tons, with deposits distributed in 75 countries. Of the existing reserves, 75% are concentrated in five countries: the United States, Russia, China, Australia, and India.

Brazil has one of the largest reserves of mineral coal in Latin America [2], and in recent years, it has been regaining its space in the energy market due to the need to supply the scarcity of electricity generated by water resources (due to seasonal lowering of water in the reservoirs). In Southern Brazil, the largest deposit in the country called Candiota Deposit is located, in which reserves of 1.2 billion tons are capable of being surface mined, at depths of up to 50 m [3].

The sequence of surface coal mining involves the previous removal of the original soil horizons, to then remove overburden rocks (**Figure 1a**,**b**, respectively). After coal seams extraction, the topographic reconstruction occurs, in which there is the return of the overburden rocks to fill the previous stripped area, and finally, the surface is leveled and topsoil is deposited to finish topographic recomposition (**Figure 1c**,**d**, respectively), creating an anthropogenic soil (**Figure 1e**).

Anthropogenic soils are soils that have been influenced, modified, or created by human activity. They are found worldwide in urban and other human-impacted landscapes. Four distinct types of anthropogenic soils can be distinguished based on geographical setting and historical context: (i) agricultural, (ii) archeological, (iii) mine-related, and (iv) urban [5]. According to the World Reference Base (WRB) [6], anthropogenic soils found in agricultural and archeological settings are classified as Anthrosols, whereas those in mine-related and urban settings are classified as Technosols. Anthrosols are formed by the transformation of natural soil by human additions of organic or inorganic materials over long periods of time, while Technosols are formed in parent materials created and deposited by human activities (e.g., mine spoils, urban fill). The most extensive mine-related anthropogenic soils are primarily associated with modern landscapes created by the surface mining of coal, and are classified as Spolic Technosols, according to the WRB, based on the fact that they contain technogenic artifacts in the form of mine spoil [5].

Before 1970s soil survey reports in the USA identified mined lands on maps and referred to them as mine dumps, mine spoils, or strip mines and mine-land reclamation its grouped surface materials on mined lands into various categories to assist

**61**

as mine soils [8].

**Figure 1.**

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

with treatment for revegetation [7]. In the 1970s, after the passage of the Surface Mining Control and Reclamation Act (SMCRA) of 1977 and the resultant state permanent regulatory programs, coal mined lands were mandated to be returned as close as possible to the approximate original landscape, and since successful revegetation was rigorously required, natural topsoil, or a topsoil substitute (in case of the pre-1970s mining), was placed at the final reclamation surface [8]. Modern mining regulations also started to require the isolation of acid-producing (FeS2) materials below the final surface. Since then, these soils, resulting from the reclamation process, have been called in the USA as minesoils [7, 9, 10], or less frequently

*Coal mining process (a-b) and topographic restoration (c-e) in southern Brazil [4].*

Minesoils, as the result of the mining and reclamation process, compared to the contiguous native soils, are much younger soils with properties more determined

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

*Mining Techniques - Past, Present and Future*

reclamation, needing re-intervention.

**2. Soils formed in surface coal mining**

China, Australia, and India.

Our study was done in a randomized block design field experiment, sampling the same soil over the time, and comparing the soil properties with the natural soil, what makes the data obtained more scientifically reliable and meaningful. We, as authors, have tried to make this idea more clear in our writing; it is well known and obvious that the soils properties once covered with vegetation will tend to improve over time. Nevertheless, this does not necessarily happen, and sometimes, many sites show signs of degradation and even erosions problems after many years of

Therefore, the main difference between our study and other similar studies is that of experimental control. Most studies deal with sampling of mining sites, with different ages, but without experimental control. It is also important to do research on soil reclamation techniques and procedures focusing on improving minesoil quality, ensuring the return of a productive soil according to the planned use.

Coal remains a major fuel in global energy systems, accounting for almost 40% of electricity generation, and over the next 5 years, the global coal demand is forecasted to remain stable, supported by the resilient Chinese market, which accounts for half of the global consumption [1]. World coal reserves have a volume of approximately 860 billion tons, with deposits distributed in 75 countries. Of the existing reserves, 75% are concentrated in five countries: the United States, Russia,

Brazil has one of the largest reserves of mineral coal in Latin America [2], and in recent years, it has been regaining its space in the energy market due to the need to supply the scarcity of electricity generated by water resources (due to seasonal lowering of water in the reservoirs). In Southern Brazil, the largest deposit in the country called Candiota Deposit is located, in which reserves of 1.2 billion tons are

The sequence of surface coal mining involves the previous removal of the original soil horizons, to then remove overburden rocks (**Figure 1a**,**b**, respectively). After coal seams extraction, the topographic reconstruction occurs, in which there is the return of the overburden rocks to fill the previous stripped area, and finally, the surface is leveled and topsoil is deposited to finish topographic recomposition

Anthropogenic soils are soils that have been influenced, modified, or created by human activity. They are found worldwide in urban and other human-impacted landscapes. Four distinct types of anthropogenic soils can be distinguished based on geographical setting and historical context: (i) agricultural, (ii) archeological, (iii) mine-related, and (iv) urban [5]. According to the World Reference Base (WRB) [6], anthropogenic soils found in agricultural and archeological settings are classified as Anthrosols, whereas those in mine-related and urban settings are classified as Technosols. Anthrosols are formed by the transformation of natural soil by human additions of organic or inorganic materials over long periods of time, while Technosols are formed in parent materials created and deposited by human activities (e.g., mine spoils, urban fill). The most extensive mine-related anthropogenic soils are primarily associated with modern landscapes created by the surface mining of coal, and are classified as Spolic Technosols, according to the WRB, based on the fact that

Before 1970s soil survey reports in the USA identified mined lands on maps and referred to them as mine dumps, mine spoils, or strip mines and mine-land reclamation its grouped surface materials on mined lands into various categories to assist

(**Figure 1c**,**d**, respectively), creating an anthropogenic soil (**Figure 1e**).

capable of being surface mined, at depths of up to 50 m [3].

they contain technogenic artifacts in the form of mine spoil [5].

**60**

**Figure 1.** *Coal mining process (a-b) and topographic restoration (c-e) in southern Brazil [4].*

with treatment for revegetation [7]. In the 1970s, after the passage of the Surface Mining Control and Reclamation Act (SMCRA) of 1977 and the resultant state permanent regulatory programs, coal mined lands were mandated to be returned as close as possible to the approximate original landscape, and since successful revegetation was rigorously required, natural topsoil, or a topsoil substitute (in case of the pre-1970s mining), was placed at the final reclamation surface [8]. Modern mining regulations also started to require the isolation of acid-producing (FeS2) materials below the final surface. Since then, these soils, resulting from the reclamation process, have been called in the USA as minesoils [7, 9, 10], or less frequently as mine soils [8].

Minesoils, as the result of the mining and reclamation process, compared to the contiguous native soils, are much younger soils with properties more determined

by human-controlled influences rather than by natural processes [9]. Their profile morphology can roughly be described as mainly composed of two layers, a surface layer made by the topsoil (the native soil A horizon) abruptly lying over a overburden layer. After few years of revegetation and exposure to climatic conditions, even in topsoil substitute layers, these young A horizons start to be loosened by root growth and organic matter accumulation and decomposition, developing color darkening and some soil structure. Also, the surface mining may accelerate the soilforming processes by breaking up the consolidated rocks of the overburden layers allowing air, water, and plant roots to penetrate this layer [6]. Therefore, in strict pedological description of horizons, usually A-C horizon sequences in very young soils (<10 years old) and A-AC-C sequences in relatively older soils (>10 years old) are found. In some older profiles (>30 years old), the beginning of formation of B horizons (Cambic) has been reported [9].

The topsoil addition surely improves the minesoil quality, but heavy machinery traffic and inadequate soil distribution can hinder the vegetation development, the main starting point for the minesoils recovery [11]. As the consequence of excessive traffic from large machines during topographic recomposition, persistent topsoil compaction (**Figure 2a**,**b**) has been reported as a major impact on the physical quality of minesoils in India [12], in China [13], in UK [14], in South Africa [15], in Germany [16], in the USA [17], and in Brazil [18].

The development and evolution of the reclaimed minesoil provides a unique opportunity to expand the existing knowledge about the formation and stabilization of aggregates, accumulation and distribution of organic matter and microbial biomass, since, due to the magnitude of the disturbance of the ecosystem, it creates a sort of "zero time" scenario [19]. The success of the minesoil recovery does not only depends on the mining methods, the height and slope of the overburden piles, the nature of the mined soils, the geoclimatic conditions, but also depends on the plant species selected for their revegetation [20]. In this sense, a great number of plant species have been researched as an alternative to recover the quality of coal minesoils in different places in the world, some of which are cited below.

#### **2.1 Reclamation of minesoils and revegetation in the USA**

Soil and plant data among a chronosequence of 19 post-mine reclaimed sites (over a 40-year reclamation gradient), and an intact native reference site were evaluated. It was noticed that root biomass in the upper horizons (at 30 cm depth) was greater on the reference site compared with the reclaimed sites as well as the

#### **Figure 2.**

*Compaction of topsoil immediately after topographic restoration of the minesoil (a) and after 8.6 years of revegetation in southern Brazil (b) [4].*

**63**

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

organic matter content, ranging from 3·5 to 5·4% on the reclaimed sites (not different across the reclamation chronosequence) and from 5·1 to 6·8% on the reference site [21]. On the other hand, in the Midwestern USA, there was the development of horizons in minesoils in a relatively short period of time (10–15 years), in which the 0.00–0.03 m layer consisted of non-decomposed or partially decomposed organic matter, while the 0.03–0.10 m layer was darker, with visible addition of organic carbon, and the 0.10–0.25 m layer was the least colored with interspersed roots [22]. When opting for the natural revegetation of mined areas, it was observed that minesoils up to 2 years of age have a predominance of annual and perennial grasses, while minesoils with 16–20 years usually have some tree species, and minesoils with

Vegetation succession and soil characteristics under five different restoration models of refuse dumps including different-aged revegetated sites were evaluated. It was observed that the biomass of the naturally species increased from 0.15 kg m−2 in the 8-year-old vegetation to 0.64 kg m−2 in the 18-year-old vegetation. Furthermore, the soil bulk density decreased from 1.56 Mg m−3 in 8-year-old vegetation on the abandoned land to 1.24 Mg m−3 for 18-year-old vegetation [24]. In another study, the minesoil showed improvements in its edaphic quality after 5 years of revegetation, which promoted an increase in the content of organic matter and a reduction in runoff and soil erosion [25]. On the other hand, the positive effects of revegetation on microbial activity were observed over 18 years

In India, carbon dynamics in one unreclaimed site (0 years) and four chronosequences revegetated coal mine sites (3, 7, 10, and 15 years) were compared with an undisturbed forest as a reference site. It was verified that soil organic carbon stock significantly increased from 0.75 Mg C ha−1 in 3 years to 7.60 Mg C ha−1 after

In Spain, the effectiveness of using native colonizer shrubs as nurse plants to reintroduce the two main tree species present before the mining operations was evaluated. It was found that the seedlings mortality under shrubs increased during the second year after plantation, probably because of the lower precipitations during the second growing season that reduced the water holding capacity of then minesoil (1–3.5 g cm−2) when compared with the nearby natural forest soil

In southeastern Nigeria, minesoils under 30 years of natural revegetation still lacked an O horizon and high values of soil density in relation to natural soil [29]. In Germany, it was observed that minesoils after 4 years of revegetation still showed very variable physical properties, and that the choice of perennial species with deeper rooting was recommended to accelerate the formation of the new soil

Minesoils that use little topsoil thickness give rise to contamination with the fragments of overburden rocks, frequently showing high soil bulk density, lower macroporosity, and high mechanical resistance to penetration, in addition to spots

**2.4 Reclamation of coal minesoils and revegetation in southern Brazil**

38–42 years old have a mix of native trees and understory species [23].

**2.3 Reclamation of minesoils and revegetation in other countries**

15 years of tree species revegetation in the top 15 cm of soils [27].

**2.2 Reclamation of minesoils and revegetation in China**

of minesoil's formation [26].

(19.8 g cm−2) [28].

structure [16].

with very low pH values (<3.0) [30].

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

*Mining Techniques - Past, Present and Future*

horizons (Cambic) has been reported [9].

Germany [16], in the USA [17], and in Brazil [18].

by human-controlled influences rather than by natural processes [9]. Their profile morphology can roughly be described as mainly composed of two layers, a surface layer made by the topsoil (the native soil A horizon) abruptly lying over a overburden layer. After few years of revegetation and exposure to climatic conditions, even in topsoil substitute layers, these young A horizons start to be loosened by root growth and organic matter accumulation and decomposition, developing color darkening and some soil structure. Also, the surface mining may accelerate the soilforming processes by breaking up the consolidated rocks of the overburden layers allowing air, water, and plant roots to penetrate this layer [6]. Therefore, in strict pedological description of horizons, usually A-C horizon sequences in very young soils (<10 years old) and A-AC-C sequences in relatively older soils (>10 years old) are found. In some older profiles (>30 years old), the beginning of formation of B

The topsoil addition surely improves the minesoil quality, but heavy machinery traffic and inadequate soil distribution can hinder the vegetation development, the main starting point for the minesoils recovery [11]. As the consequence of excessive traffic from large machines during topographic recomposition, persistent topsoil compaction (**Figure 2a**,**b**) has been reported as a major impact on the physical quality of minesoils in India [12], in China [13], in UK [14], in South Africa [15], in

The development and evolution of the reclaimed minesoil provides a unique opportunity to expand the existing knowledge about the formation and stabilization of aggregates, accumulation and distribution of organic matter and microbial biomass, since, due to the magnitude of the disturbance of the ecosystem, it creates a sort of "zero time" scenario [19]. The success of the minesoil recovery does not only depends on the mining methods, the height and slope of the overburden piles, the nature of the mined soils, the geoclimatic conditions, but also depends on the plant species selected for their revegetation [20]. In this sense, a great number of plant species have been researched as an alternative to recover the quality of coal

Soil and plant data among a chronosequence of 19 post-mine reclaimed sites (over a 40-year reclamation gradient), and an intact native reference site were evaluated. It was noticed that root biomass in the upper horizons (at 30 cm depth) was greater on the reference site compared with the reclaimed sites as well as the

*Compaction of topsoil immediately after topographic restoration of the minesoil (a) and after 8.6 years of* 

minesoils in different places in the world, some of which are cited below.

**2.1 Reclamation of minesoils and revegetation in the USA**

**62**

**Figure 2.**

*revegetation in southern Brazil (b) [4].*

organic matter content, ranging from 3·5 to 5·4% on the reclaimed sites (not different across the reclamation chronosequence) and from 5·1 to 6·8% on the reference site [21]. On the other hand, in the Midwestern USA, there was the development of horizons in minesoils in a relatively short period of time (10–15 years), in which the 0.00–0.03 m layer consisted of non-decomposed or partially decomposed organic matter, while the 0.03–0.10 m layer was darker, with visible addition of organic carbon, and the 0.10–0.25 m layer was the least colored with interspersed roots [22]. When opting for the natural revegetation of mined areas, it was observed that minesoils up to 2 years of age have a predominance of annual and perennial grasses, while minesoils with 16–20 years usually have some tree species, and minesoils with 38–42 years old have a mix of native trees and understory species [23].

#### **2.2 Reclamation of minesoils and revegetation in China**

Vegetation succession and soil characteristics under five different restoration models of refuse dumps including different-aged revegetated sites were evaluated. It was observed that the biomass of the naturally species increased from 0.15 kg m−2 in the 8-year-old vegetation to 0.64 kg m−2 in the 18-year-old vegetation. Furthermore, the soil bulk density decreased from 1.56 Mg m−3 in 8-year-old vegetation on the abandoned land to 1.24 Mg m−3 for 18-year-old vegetation [24]. In another study, the minesoil showed improvements in its edaphic quality after 5 years of revegetation, which promoted an increase in the content of organic matter and a reduction in runoff and soil erosion [25]. On the other hand, the positive effects of revegetation on microbial activity were observed over 18 years of minesoil's formation [26].

#### **2.3 Reclamation of minesoils and revegetation in other countries**

In India, carbon dynamics in one unreclaimed site (0 years) and four chronosequences revegetated coal mine sites (3, 7, 10, and 15 years) were compared with an undisturbed forest as a reference site. It was verified that soil organic carbon stock significantly increased from 0.75 Mg C ha−1 in 3 years to 7.60 Mg C ha−1 after 15 years of tree species revegetation in the top 15 cm of soils [27].

In Spain, the effectiveness of using native colonizer shrubs as nurse plants to reintroduce the two main tree species present before the mining operations was evaluated. It was found that the seedlings mortality under shrubs increased during the second year after plantation, probably because of the lower precipitations during the second growing season that reduced the water holding capacity of then minesoil (1–3.5 g cm−2) when compared with the nearby natural forest soil (19.8 g cm−2) [28].

In southeastern Nigeria, minesoils under 30 years of natural revegetation still lacked an O horizon and high values of soil density in relation to natural soil [29].

In Germany, it was observed that minesoils after 4 years of revegetation still showed very variable physical properties, and that the choice of perennial species with deeper rooting was recommended to accelerate the formation of the new soil structure [16].

#### **2.4 Reclamation of coal minesoils and revegetation in southern Brazil**

Minesoils that use little topsoil thickness give rise to contamination with the fragments of overburden rocks, frequently showing high soil bulk density, lower macroporosity, and high mechanical resistance to penetration, in addition to spots with very low pH values (<3.0) [30].

Attributes of minesoil under the cultivation of *Hemarthria altissima*, *Paspalum notatum* cv. Pensacola, *Cynodon dactylon* cv. Tifton, and *Urochloa brizantha* were evaluated in a randomized block design experiment at 5 [31], 41 [32], 72 [33, 34], 78 [35], and 103 months [36]. The results are reported below:


**65**

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

within the same layer of the minesoil.

**case study at the Candiota coal mine**

replicates (each plot with 4 × 5 m = 20 m<sup>2</sup>

natural soil under native vegetation (reference soil).

different plants species.

aggregates than the 0.10–0.20 m layer. From this point on, aggregation would begin to develop with the action of decomposed roots and microorganisms favoring the conglomeration of particles, with sequential reformation and stabilization of aggregates, following the traditional soil-aggregation hierarchy path. As the root system progressively reaches and develops in the 0.10–0.20 m layer, the same process mentioned above is expected to occur. It is important to mention that all hierarchical levels mentioned above can occur simultaneously

**3. Physical and biological attributes of minesoil revegetated with** 

**perennial grasses compared with the natural soil in southern Brazil: a** 

In late 2003, a field experiment located at a reclaimed site in the Candiota coal mine (31°33′56″ S and 53°43′30″ W) was implemented, under concession of the Riograndense Mining Company, and the research group from the Pelotas Federal University has been conducting a long-term experiment on the soil quality with

The topsoil used to cover the coal overburden was composed mainly by the B horizon of the natural soil (prior to mining), a Rhodic Lixisol [6], with high clay content (466 g kg−1 clay), dark red color (2.5 YR 3/6), and lower organic matter content (12 g kg−1) compared to the A horizon (21 g kg−1). The experiment was installed in November/December 2003 in a randomized block design with four

of perennial summer grasses (**Figure 3**): *Hemarthria altissima* (15 cuttings m−2), *Paspalum notatum* cv. Pensacola (50 kg of seed ha−1), *Cynodon dactylon* cv. Tifton (15 cuttings m−2), and *Urochloa brizantha* (10 kg of seed ha−1). Prior to the implantation of the cover crops, the soil was chiseled with a bulldozer up to 0.15 m depth, and also received dolomitic limestone equivalent to 10.4 Mg ha−1 effective calcium carbonate rating and 900 kg ha−1 of NPK fertilizer, 5-20-20 (45 kg N, 180 kg P2O5, and 180 kg K2O). Annually, all plots received 250 kg ha−1 of NPK fertilizer, 5-30-15 (12.5 kg N, 75 kg P2O5, and 37.5 kg K2O) and 250 kg ha−1 of ammonium sulfate. In July 2012 (8.6 years of revegetation), soil samples in the 0.00–0.10 m and 0.10–0.20 m layers were collected in minesoil and natural soil to determine the granulometry [37], tensile strength [38, 39], distribution of water stable aggregates in size classes [40, 41], bulk density and soil porosity, and the organic carbon content [42]. In October 2014 (10.9 years of revegetation), the soil samples in the 0.00–0.10 m layer were collected to determine the microbial biomass carbon [43], metabolic quotient [44], and organisms of the edaphic mesofauna, represented by mites and springtails [45]. All soil attributes differences were compared to the

The predominant natural soil of the mining area is a Rhodic Lixisol with 477.79 g kg−1 sand, 271.81 g kg−1 silt, and 250.40 g kg−1 clay in the 0.00–0.10 m layer, and 444.91 g kg−1 sand, 256.09 g kg−1 of silt, and 299.00 g kg−1 of clay in the 0.10–0.20 m layer [4]. Due to the soil construction processes, both the 0.00–0.10 and 0.10–0.20 m layers of the minesoil present, respectively, 80.91 and 59.87% higher clay content (453 and 478 g kg−1, respectively) than the non-anthropized natural soil. Differences in clay content can make attribute comparisons between minesoils and natural soils questionable, as higher clay contents contribute to greater aggregation through the reorientation of clay particles, binding with root exudates and wetting and drying cycles. By contrast, measuring soil attributes prior to coal mining allows one to understand the intensity of the impact of mining

). Grasses used as treatments consisted

*Mining Techniques - Past, Present and Future*

5.18 g kg−1.

6.20 g kg−1.

*brizantha* (118 kPa).

(0.61 Mg ha−1).

103 months [36]. The results are reported below:

Attributes of minesoil under the cultivation of *Hemarthria altissima*, *Paspalum notatum* cv. Pensacola, *Cynodon dactylon* cv. Tifton, and *Urochloa brizantha* were evaluated in a randomized block design experiment at 5 [31], 41 [32], 72 [33, 34], 78 [35], and

a.At 5 months of revegetation, there were no differences in the attributes of the minesoil under the different species. However, the highest concentration of aggregates in the 0.00–0.10 m layer occurred in the 1.00–0.25 mm class (32.67%), while in the 0.10–0.20 m layer, the highest concentration occurred in the 4.76–2.00 mm class (26.68%). The average carbon content in the 0.00–0.10 m layer was 5.34 g kg−1 and in the 0.10–0.20 m layer, it was

b.At 41 months of revegetation, there were also no differences in soil attributes under the different species. However, the highest concentration of aggregates occurred in the 1.00–0.25 mm class, both in the 0.00–0.10 m layer (40.13%) and in the 0.10–0.20 m layer (35. 73%). The average organic carbon content in the 0.00–0.10 m layer was 7.38 g kg−1 and in the 0.10–0.20 m layer, it was

c.At 72 months of revegetation, in the 0.00–0.05 m layer, the lowest value of the pre-consolidation pressure was provided by *Hemarthria altissima* (71 kPa) while the other plant species showed higher values provided: *Paspalum notatum* cv. Pensacola (120 KPa), *Cynodon dactylon* cv. Tifton (120 kPa), and *Urochloa* 

d.Also at 72 months of revegetation, in the 0.00–0.03 m layer, it was observed that *Hemarthria altissima* and *Urochloa brizantha* provided the highest carbon stocks in the light free fraction (1.22 Mg ha−1 and 1.27 Mg ha−1, respectively) compared to *Paspalum notatum* (0.86 Mg ha−1) and *Cynodon dactylon* (0.83 Mg ha−1). In relation to the carbon stock of the light occluded fraction, *Hemarthria altissima* and *Cynodon dactylon* presented higher stocks (1.09 Mg ha−1 and 1.02 Mg ha−1, respectively) compared to *Paspalum notatum*

e.At 78 months of revegetation, it was found that concentration of macroaggregates was higher in the 0.10–0.20 m layer (87.56%) compared with the 0.00– 0.10 m layer (81.15%). Average organic carbon content in the 0.00–0.10 m layer was 8.46 g kg−1 and in the 0.10–0.20 m layer, it was 6.39 g kg−1.

f. After 103 months of revegetation, root's perennial grasses concentration and minesoil physical attributes were measured. It was verified that the root mass concentration ranged from 66 to 81% in the 0.00–0.10 m layer decreasing to 13–28% in the 0.10–0.20 m layer, due to inadequate physical conditions below the 0.00–0.10 m layer, indicated by macroporosity values below 0.10 m3

bulk density greater than 1.40 Mg m−3, and the highest percentage of macroaggregates with large, cohesive, and sharp-edged aggregates features. In relation to this, a different soil-aggregation hierarchy path in clay minesoils with highly compacted topsoil was proposed, in which, prior to revegetation, compacted aggregates arising from the compression of the soil mass made by the intense movement of heavy machinery were produced during topographical recomposition. Thus, in the first year after revegetation, the 0.00–0.10 m soil layer presented smaller aggregates arising from the breakdown of the large cohesive

m−3,

**64**

aggregates than the 0.10–0.20 m layer. From this point on, aggregation would begin to develop with the action of decomposed roots and microorganisms favoring the conglomeration of particles, with sequential reformation and stabilization of aggregates, following the traditional soil-aggregation hierarchy path. As the root system progressively reaches and develops in the 0.10–0.20 m layer, the same process mentioned above is expected to occur. It is important to mention that all hierarchical levels mentioned above can occur simultaneously within the same layer of the minesoil.

#### **3. Physical and biological attributes of minesoil revegetated with perennial grasses compared with the natural soil in southern Brazil: a case study at the Candiota coal mine**

In late 2003, a field experiment located at a reclaimed site in the Candiota coal mine (31°33′56″ S and 53°43′30″ W) was implemented, under concession of the Riograndense Mining Company, and the research group from the Pelotas Federal University has been conducting a long-term experiment on the soil quality with different plants species.

The topsoil used to cover the coal overburden was composed mainly by the B horizon of the natural soil (prior to mining), a Rhodic Lixisol [6], with high clay content (466 g kg−1 clay), dark red color (2.5 YR 3/6), and lower organic matter content (12 g kg−1) compared to the A horizon (21 g kg−1). The experiment was installed in November/December 2003 in a randomized block design with four replicates (each plot with 4 × 5 m = 20 m<sup>2</sup> ). Grasses used as treatments consisted of perennial summer grasses (**Figure 3**): *Hemarthria altissima* (15 cuttings m−2), *Paspalum notatum* cv. Pensacola (50 kg of seed ha−1), *Cynodon dactylon* cv. Tifton (15 cuttings m−2), and *Urochloa brizantha* (10 kg of seed ha−1). Prior to the implantation of the cover crops, the soil was chiseled with a bulldozer up to 0.15 m depth, and also received dolomitic limestone equivalent to 10.4 Mg ha−1 effective calcium carbonate rating and 900 kg ha−1 of NPK fertilizer, 5-20-20 (45 kg N, 180 kg P2O5, and 180 kg K2O). Annually, all plots received 250 kg ha−1 of NPK fertilizer, 5-30-15 (12.5 kg N, 75 kg P2O5, and 37.5 kg K2O) and 250 kg ha−1 of ammonium sulfate.

In July 2012 (8.6 years of revegetation), soil samples in the 0.00–0.10 m and 0.10–0.20 m layers were collected in minesoil and natural soil to determine the granulometry [37], tensile strength [38, 39], distribution of water stable aggregates in size classes [40, 41], bulk density and soil porosity, and the organic carbon content [42]. In October 2014 (10.9 years of revegetation), the soil samples in the 0.00–0.10 m layer were collected to determine the microbial biomass carbon [43], metabolic quotient [44], and organisms of the edaphic mesofauna, represented by mites and springtails [45]. All soil attributes differences were compared to the natural soil under native vegetation (reference soil).

The predominant natural soil of the mining area is a Rhodic Lixisol with 477.79 g kg−1 sand, 271.81 g kg−1 silt, and 250.40 g kg−1 clay in the 0.00–0.10 m layer, and 444.91 g kg−1 sand, 256.09 g kg−1 of silt, and 299.00 g kg−1 of clay in the 0.10–0.20 m layer [4]. Due to the soil construction processes, both the 0.00–0.10 and 0.10–0.20 m layers of the minesoil present, respectively, 80.91 and 59.87% higher clay content (453 and 478 g kg−1, respectively) than the non-anthropized natural soil. Differences in clay content can make attribute comparisons between minesoils and natural soils questionable, as higher clay contents contribute to greater aggregation through the reorientation of clay particles, binding with root exudates and wetting and drying cycles. By contrast, measuring soil attributes prior to coal mining allows one to understand the intensity of the impact of mining

**Figure 3.** *Hemarthria altissima (a), Paspalum notatum cv. Pensacola (b), Cynodon dactylon cv. Tifton (c), and Urochloa brizantha (d) implanted in minesoil in southern Brazil [4].*

on the environment. Consequently, the differences between the attributes of the natural and the minesoil are important in estimating the recovery period required for the new soil profile to perform functions in the environment in which it is inserted.

In this sense, after 8.6 years of revegetation, it is possible to observe that the minesoil under *Urochloa brizantha* and *Paspalum notatum* presented in the 0.00– 0.10 m layer, respectively, 1.8 and 5.7% lower percentages of macroaggregates, while the constructed soil under *Hemarthria altissima* and *Cynodon dactylon* presented, respectively, 2.4 and 3.5% higher percentages of macroaggregates in relation to the natural soil (89.15%). In the 0.10–0.20 m layer, the treatments presented 16.4–19.2% higher percentage of macroaggregates in relation to the reference soil (80.65%) (**Figure 4a**). The largest proportion of macroaggregates presented by minesoil below the 10 cm layer, relative to natural soil, does not refer to a natural aggregation process promoted by biological forces (roots and exudates of microorganisms), but formed by the compression generated by intensive machines traffic during the topographic recomposition of the mined area [36].

Regarding the percentage of microaggregates, it was observed that in the 0.00–0.10 m layer, *Urochloa brizantha* and *Paspalum notatum* promoted, respectively, 46.9 and 14.9% higher percentage, while *Hemarthria altissima* and *Cynodon dactylon* promoted, respectively, 19.5 and 18.5% lower percentage than the reference soil (10.85%). In the 0.10–0.20 m layer, the treatments presented 68.6–80.2% lower microaggregation than the natural soil under native vegetation (19.35%) (**Figure 4b**). In a minesoil in the USA [39], macroaggregation was 50% smaller and microaggregation was 10% smaller in less than 1 year old soil (64% sand, 22% silt, and 19% clay) when compared to natural soil (55% sand, 29% silt, and 16% clay). However, after 16–20 years of revegetation, there was similarity between the distribution of minesoil aggregates (56% sand, 31% silt, and 13% clay) in relation to soils not disturbed by coal mining (59% sand, 28% silt, and 13% clay).

**Figure 5** shows that in the minesoil under the perennial grasses, the aggregates presented 24.9–66% higher tensile strength compared to the natural soil (55.98 kPa) in the 0.00–0.10 m layer, while in the 0.10–0.20 m, the tensile strength values of the treatments were 163.9–221% higher than the reference soil (66.28 kPa). Similar results in a coal minesoil after 2.8 years of revegetation was observed, with higher tensile strength values in the 0.00–0.05 m (70.32–88.81 kPa) and 0.10–0.15 m (70.90–125.92 kPa) layers of grass covered in comparison to the natural soil under

**67**

(1.26 Mg m−3) [48].

poor porous aggregates [38].

**Figure 4.**

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

native vegetation (0.00–0.05 m: 55.98 kPa, and 0.10–0.15 m: 66.28 kPa) [46]. The higher tensile strength of aggregates is due to the effect of machine traffic during the topographic recomposition of the area, which resulted in cohesive, hard, and

*of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

*Differences (Δtest) between percentage macroaggregates (a) and microaggregates (b) of minesoil after 8.6 years* 

After 8.6 years of revegetation, it was also observed that the minesoil under different perennial grasses presented soil bulk density up to 21.1% higher in the 0.00–0.10 m layer, while in the 0.10–0.20 m layer, the difference was 15.7–34.05% in relation to the natural soil under native revegetation (presented 1.20 Mg m−3 and 1.18 Mg m−3, respectively) (**Figure 6**). This result is due to topsoil compaction during the topographic recomposition of the mined area, commonly cited in the literature [47]. On the other hand, other studies indicate that the bulk density decreases over time, as observed in a minesoil in the USA, which is presented at 5, 10, and 16 years of revegetation values of 1.82 Mg m−3 (69% sand, 21% silt, and 10% clay), 1.70 Mg m−3 (50% sand, 28% silt, and 22% clay), and 1.48 Mg m−3 after 16 years (44% sand, 32% silt, and 24% clay). However, even after 16 years of revegetation, the bulk density was higher than the natural soil under grass

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

**Figure 4.**

*Mining Techniques - Past, Present and Future*

on the environment. Consequently, the differences between the attributes of the natural and the minesoil are important in estimating the recovery period required for the new soil profile to perform functions in the environment in which it is

*Hemarthria altissima (a), Paspalum notatum cv. Pensacola (b), Cynodon dactylon cv. Tifton (c), and* 

*Urochloa brizantha (d) implanted in minesoil in southern Brazil [4].*

In this sense, after 8.6 years of revegetation, it is possible to observe that the minesoil under *Urochloa brizantha* and *Paspalum notatum* presented in the 0.00– 0.10 m layer, respectively, 1.8 and 5.7% lower percentages of macroaggregates, while the constructed soil under *Hemarthria altissima* and *Cynodon dactylon* presented, respectively, 2.4 and 3.5% higher percentages of macroaggregates in relation to the natural soil (89.15%). In the 0.10–0.20 m layer, the treatments presented 16.4–19.2% higher percentage of macroaggregates in relation to the reference soil (80.65%) (**Figure 4a**). The largest proportion of macroaggregates presented by minesoil below the 10 cm layer, relative to natural soil, does not refer to a natural aggregation process promoted by biological forces (roots and exudates of microorganisms), but formed by the compression generated by intensive machines traffic

Regarding the percentage of microaggregates, it was observed that in the 0.00–0.10 m layer, *Urochloa brizantha* and *Paspalum notatum* promoted, respectively, 46.9 and 14.9% higher percentage, while *Hemarthria altissima* and *Cynodon dactylon* promoted, respectively, 19.5 and 18.5% lower percentage than the reference soil (10.85%). In the 0.10–0.20 m layer, the treatments presented 68.6–80.2% lower microaggregation than the natural soil under native vegetation (19.35%) (**Figure 4b**). In a minesoil in the USA [39], macroaggregation was 50% smaller and microaggregation was 10% smaller in less than 1 year old soil (64% sand, 22% silt, and 19% clay) when compared to natural soil (55% sand, 29% silt, and 16% clay). However, after 16–20 years of revegetation, there was similarity between the distribution of minesoil aggregates (56% sand, 31% silt, and 13% clay) in relation to

soils not disturbed by coal mining (59% sand, 28% silt, and 13% clay).

**Figure 5** shows that in the minesoil under the perennial grasses, the aggregates presented 24.9–66% higher tensile strength compared to the natural soil (55.98 kPa) in the 0.00–0.10 m layer, while in the 0.10–0.20 m, the tensile strength values of the treatments were 163.9–221% higher than the reference soil (66.28 kPa). Similar results in a coal minesoil after 2.8 years of revegetation was observed, with higher tensile strength values in the 0.00–0.05 m (70.32–88.81 kPa) and 0.10–0.15 m (70.90–125.92 kPa) layers of grass covered in comparison to the natural soil under

during the topographic recomposition of the mined area [36].

**66**

inserted.

**Figure 3.**

*Differences (Δtest) between percentage macroaggregates (a) and microaggregates (b) of minesoil after 8.6 years of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

native vegetation (0.00–0.05 m: 55.98 kPa, and 0.10–0.15 m: 66.28 kPa) [46]. The higher tensile strength of aggregates is due to the effect of machine traffic during the topographic recomposition of the area, which resulted in cohesive, hard, and poor porous aggregates [38].

After 8.6 years of revegetation, it was also observed that the minesoil under different perennial grasses presented soil bulk density up to 21.1% higher in the 0.00–0.10 m layer, while in the 0.10–0.20 m layer, the difference was 15.7–34.05% in relation to the natural soil under native revegetation (presented 1.20 Mg m−3 and 1.18 Mg m−3, respectively) (**Figure 6**). This result is due to topsoil compaction during the topographic recomposition of the mined area, commonly cited in the literature [47]. On the other hand, other studies indicate that the bulk density decreases over time, as observed in a minesoil in the USA, which is presented at 5, 10, and 16 years of revegetation values of 1.82 Mg m−3 (69% sand, 21% silt, and 10% clay), 1.70 Mg m−3 (50% sand, 28% silt, and 22% clay), and 1.48 Mg m−3 after 16 years (44% sand, 32% silt, and 24% clay). However, even after 16 years of revegetation, the bulk density was higher than the natural soil under grass (1.26 Mg m−3) [48].

#### **Figure 5.**

*Differences (Δtest) between tensile strength aggregates of minesoil after 8.6 years of revegetation (under perennial grasses) relative to the natural soil (under native vegetation).*

#### **Figure 6.**

*Differences (Δtest) between the bulk density of minesoil after 8.6 years of revegetation (under perennial grasses) relative to the natural soil (under native vegetation).*

When evaluating pore distribution, it was observed that in the 0.00–0.10 m layer, the minesoil under *Urochloa brizantha* and *Cynodon dactylon* presented, respectively, 26.4 and 25.9% higher macroporosity than the natural soil under native vegetation, while the other species presented lower values, highlighting the potential of the root system of these species, which presented in the layer of 0.00–0.10 m 92 and 93% of their roots with a diameter smaller than 0.49 mm [18]. However, below the 0.10–0.20 m layer, it was observed that the treatments presented 4.9–70.5% lower macroporosity than the reference soil (**Figure 7**), which was the consequence of the higher degree of compaction of minesoil.

The results presented show the difficulty in revegetating mined areas and, consequently, in allowing the natural incorporation of organic waste in the minesoils [49], which directly influences the regeneration of these areas. **Figure 8** shows that the organic carbon content of the minesoil was 48.3–58.2% lower in the 0.00–0.10 m layer compared to the natural soil (20.04 g kg−1), while in the 0.10– 0.20 m layer, the values were 18.6–53.1% lower than the natural soil (10.26 g kg−1).

**69**

**Figure 7.**

**Figure 8.**

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

*grasses) relative to natural soil (under native vegetation).*

However, in a minesoil in the USA, higher levels of organic carbon were observed in minesoils after 14 years (19.7 Mg ha−1) and 26 years (13.4 Mg ha−1) of revegetation

*Differences (Δtest) between the organic carbon content of minesoil after 8.6 years of revegetation (under* 

*Differences (Δtest) between the macroporosity of minesoil after 8.6 years of revegetation (under perennial* 

The higher carbon content in natural soil is linked to the presence of microorganisms in the soil. In this sense, after 10.9 years of revegetation, it was observed that the natural soil presented 373 g kg−1of microbial biomass carbon in the 0.00– 0.10 m layer. The minesoil under the different grasses presented up to 42.69% lower values, except the soil under *Hemarthria altissima*, which presented values similar to the natural soil (**Figure 9a**). This result highlights the importance of adding carbon sources in recovering areas, aiming at the improvement of biochemical conditions,

On the other hand, **Figure 9b** shows that the metabolic quotient (qCO2) values in the 0.00–0.10 m layer of the minesoil were 23.4 and 103.1% higher than the natural soil (0.64). A high qCO2 indicates that the microbial population is experiencing

than the natural soil (9.92 Mg ha−1) [48].

which may favor the return of soil biological balance.

*perennial grasses) relative to the natural soil (under native vegetation).*

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

#### **Figure 7.**

*Mining Techniques - Past, Present and Future*

When evaluating pore distribution, it was observed that in the 0.00–0.10 m layer, the minesoil under *Urochloa brizantha* and *Cynodon dactylon* presented, respectively, 26.4 and 25.9% higher macroporosity than the natural soil under native vegetation, while the other species presented lower values, highlighting the potential of the root system of these species, which presented in the layer of 0.00–0.10 m 92 and 93% of their roots with a diameter smaller than 0.49 mm [18]. However, below the 0.10–0.20 m layer, it was observed that the treatments presented 4.9–70.5% lower macroporosity than the reference soil (**Figure 7**), which

*Differences (Δtest) between the bulk density of minesoil after 8.6 years of revegetation (under perennial* 

*Differences (Δtest) between tensile strength aggregates of minesoil after 8.6 years of revegetation (under* 

*perennial grasses) relative to the natural soil (under native vegetation).*

*grasses) relative to the natural soil (under native vegetation).*

The results presented show the difficulty in revegetating mined areas and, consequently, in allowing the natural incorporation of organic waste in the minesoils [49], which directly influences the regeneration of these areas. **Figure 8** shows that the organic carbon content of the minesoil was 48.3–58.2% lower in the 0.00–0.10 m layer compared to the natural soil (20.04 g kg−1), while in the 0.10– 0.20 m layer, the values were 18.6–53.1% lower than the natural soil (10.26 g kg−1).

was the consequence of the higher degree of compaction of minesoil.

**68**

**Figure 5.**

**Figure 6.**

*Differences (Δtest) between the macroporosity of minesoil after 8.6 years of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

#### **Figure 8.**

*Differences (Δtest) between the organic carbon content of minesoil after 8.6 years of revegetation (under perennial grasses) relative to the natural soil (under native vegetation).*

However, in a minesoil in the USA, higher levels of organic carbon were observed in minesoils after 14 years (19.7 Mg ha−1) and 26 years (13.4 Mg ha−1) of revegetation than the natural soil (9.92 Mg ha−1) [48].

The higher carbon content in natural soil is linked to the presence of microorganisms in the soil. In this sense, after 10.9 years of revegetation, it was observed that the natural soil presented 373 g kg−1of microbial biomass carbon in the 0.00– 0.10 m layer. The minesoil under the different grasses presented up to 42.69% lower values, except the soil under *Hemarthria altissima*, which presented values similar to the natural soil (**Figure 9a**). This result highlights the importance of adding carbon sources in recovering areas, aiming at the improvement of biochemical conditions, which may favor the return of soil biological balance.

On the other hand, **Figure 9b** shows that the metabolic quotient (qCO2) values in the 0.00–0.10 m layer of the minesoil were 23.4 and 103.1% higher than the natural soil (0.64). A high qCO2 indicates that the microbial population is experiencing

**Figure 9.**

*Differences (Δtest) between microbial biomass carbon (a) and metabolic quotient (b) of minesoil after 10.9 years of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

#### **Figure 10.**

*Differences (Δtest) between the mites (a) and springtails population (b) of minesoil after 10.9 years of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

high energy expenditure in maintaining it with greater respiration and CO2 release rather than less carbon uptake into microbial cells.

Regarding the edaphic mesofauna, after 10.9 years of revegetation, the minesoil had a smaller mite population (between −24.6 and −80.6%) and a smaller springtail population (between −56 and −100%) compared to the reference soil. (**Figure 10a,b**), which was the consequence of the degraded state of the minesoil. On the other hand, it was observed that mites were larger than springtails population in both constructed minesoil and natural soil. This result is coherent because mites occur more in the interior of the soil, while the springtails occur on the surface [26].

According to the research results, it can be seen that the recovery of minesoils was more effective after 8.6 years of revegetation only in the physical condition up to 0.10 m depth. However, all the soil physical attributes and organic matter content are still far from the levels observed in the natural soil. The use of species with a more aggressive root system, such as the species selected in the present study (perennial grasses), possibly contributed to the positive results obtained in the short term, while it is expected that a following similar period (i.e., mid-term) is necessary for improvements in physical attributes below the 0.10 m layer.

About biological attributes, the 10.9 years of revegetation have not been sufficient yet to restore a mites and springtails population close to the natural soil.

**71**

**Author details**

Pelotas, Brazil

Luiz Fernando Spinelli Pinto1

Leonir Aldrighi Dutra Junior2

and Mauricio Silva e Oliveira1

, Lizete Stumpf<sup>1</sup>

1 Agronomy College, Federal University of Pelotas, Brazil

institute where the work has been carried out.

\*Address all correspondence to: zete.stumpf@gmail.com

provided the original work is properly cited.

, Jeferson Diego Leidemer2

Research results show that the reclaimed soils properties in coal mining areas, even after several years of reclamation, are still evolving and behind the quality of natural soils, especially the physical properties. This means that the reclaimed soil after mine decommissioning will be probably more fragile under cultivation than the natural soils, implying farmers to increase soils conservationist care in the first years. It is advisable that mining companies be aware of this and recommend farmers to cultivate the reclaimed soils using conservation systems, like no tillage

The authors would like to acknowledge Companhia Riograndense de Mineração

The manuscript is original, has not been published before, and is not being considered for publication elsewhere in its final form neither in printed nor in electronic format and does not present any kind of conflict of interests. The publication has been approved by all coauthors as well as by the responsible authorities at the

(CRM), Brazilian Coal Network, CAPES e CNPq for logistical and financial

systems, always maintaining straw covering on the soil's surface.

2 Soil and Water Management and Conservation Program, Federal University of

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*, Pablo Miguel1

,

, Lucas da Silva Barbosa2

*Reclamation of Soils Degraded by Surface Coal Mining DOI: http://dx.doi.org/10.5772/intechopen.93432*

**4. Final considerations**

**Acknowledgements**

**Conflict of interest**

support.

### **4. Final considerations**

*Mining Techniques - Past, Present and Future*

high energy expenditure in maintaining it with greater respiration and CO2 release

*Differences (Δtest) between the mites (a) and springtails population (b) of minesoil after 10.9 years of* 

*Differences (Δtest) between microbial biomass carbon (a) and metabolic quotient (b) of minesoil after 10.9 years of revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

*revegetation (under perennial grasses) relative to natural soil (under native vegetation).*

Regarding the edaphic mesofauna, after 10.9 years of revegetation, the minesoil had a smaller mite population (between −24.6 and −80.6%) and a smaller springtail population (between −56 and −100%) compared to the reference soil. (**Figure 10a,b**), which was the consequence of the degraded state of the minesoil. On the other hand, it was observed that mites were larger than springtails population in both constructed minesoil and natural soil. This result is coherent because mites occur more in the interior of the soil, while the springtails occur on the

According to the research results, it can be seen that the recovery of minesoils was more effective after 8.6 years of revegetation only in the physical condition up to 0.10 m depth. However, all the soil physical attributes and organic matter content are still far from the levels observed in the natural soil. The use of species with a more aggressive root system, such as the species selected in the present study (perennial grasses), possibly contributed to the positive results obtained in the short term, while it is expected that a following similar period (i.e., mid-term) is necessary for improvements in physical attributes below the

About biological attributes, the 10.9 years of revegetation have not been sufficient yet to restore a mites and springtails population close to the natural soil.

rather than less carbon uptake into microbial cells.

**70**

surface [26].

**Figure 10.**

**Figure 9.**

0.10 m layer.

Research results show that the reclaimed soils properties in coal mining areas, even after several years of reclamation, are still evolving and behind the quality of natural soils, especially the physical properties. This means that the reclaimed soil after mine decommissioning will be probably more fragile under cultivation than the natural soils, implying farmers to increase soils conservationist care in the first years. It is advisable that mining companies be aware of this and recommend farmers to cultivate the reclaimed soils using conservation systems, like no tillage systems, always maintaining straw covering on the soil's surface.

### **Acknowledgements**

The authors would like to acknowledge Companhia Riograndense de Mineração (CRM), Brazilian Coal Network, CAPES e CNPq for logistical and financial support.

### **Conflict of interest**

The manuscript is original, has not been published before, and is not being considered for publication elsewhere in its final form neither in printed nor in electronic format and does not present any kind of conflict of interests. The publication has been approved by all coauthors as well as by the responsible authorities at the institute where the work has been carried out.

### **Author details**

Luiz Fernando Spinelli Pinto1 , Lizete Stumpf<sup>1</sup> \*, Pablo Miguel1 , Leonir Aldrighi Dutra Junior2 , Jeferson Diego Leidemer2 , Lucas da Silva Barbosa2 and Mauricio Silva e Oliveira1

1 Agronomy College, Federal University of Pelotas, Brazil

2 Soil and Water Management and Conservation Program, Federal University of Pelotas, Brazil

\*Address all correspondence to: zete.stumpf@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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to different soil tillage systems. Revista Brasileira de Ciência do Solo.

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Agricultural Research Corporation) – Centro Nacional de Pesquisa de Solos (Soils Research Center). Manual de Métodos de Análise de Solo. Rio de Janeiro: EMBRAPA-CNPS; 2011

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quantitative measurement of microbial

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still.2016.03.005

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Pedon development on a mined

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[31] Franco AMP. Caracterização física de um solo construído na área de mineração de carvão de Candiota-RS [dissertation]. Universidade Federal de

[32] Gonçalves FC. Efeito de plantas de cobertura sobre os atributos físicos de um solo construído na área de mineração de carvão de Candiota-RS após três anos [dissertation]. Pelotas: Universidade

[33] Miola ECC. Qualidade física de um solo construído e cultivado com diferentes plantas de cobertura na área de mineração de Candiota—RS [dissertation]. Pelotas: Universidade

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[35] Catro RC. Avaliação temporal de atributos físicos de um solo construído em área de mineração de carvão recuperado com gramíneas perenes [dissertation]. Pelotas: Universidade

[36] Stumpf L, Pauletto EA, Pinto LFS. Soil aggregation and root growth of perennial grasses in a constructed clay

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[49] Anderson JD, Ingram LJ, Stahl PD. Influence of reclamation management practices on microbial biomass carbon and soil organic carbon accumulation in semiarid mined lands of Wyoming. Applied Soil Ecology. 2008;**40**:387-397

**77**

Section 2

Mining Techniques -

Future

### Section 2
