*4.1.2 Classifications containing stand-up time*

Lauffer (1958) anticipated that stand up time for an excavation span is associated with the quality of rock mass in which the width is mined. The Unsupported span may be defined as the width of the tunnel or the distance between the face and the adjacent support, if such is grater that the tunnels width. Laufer's (1958)

advanced classification has been improved by various researchers especially Pacher et al., (1974) and currently formulae the part of the worldwide tunneling attitude so called the New Austrian Tunneling Method (NTAM). The importance of the standup time is to increase in the tunnel width results in a substantial decrease in the period available for the fixing of support. The NATM comprises numerous systems for workable, safe and stable excavation in rock situations where the stand-up time is restricted before collapse occurred. These systems are:


As described by Terzaghi (1946), these practices are appropriate to apply in squeezing soft rock mass i.e. shale's, phyllites and mudstones. The practices are also appropriate when tunneling in exceptionally jointed rock, but needs excessive attention to apply these practices to underground excavations designed in hard rocks having dissimilar failure mechanisms. For hard rock excavation support design, it is practical to accept the assumption that the stability of the rock mass adjacent to the underground excavation is not time-dependent. A defined wedge visible in the roof of an excavation will fall as soon as after excavation. This can happen after blasting or during the succeeding scaling process. Early support is demanded do keep such a wedge in place, or to improve the limit of safety preferably before the rock supporting the full wedge is removed. On the other hand, in a highly stressed rock condition, failure will generally be induced by some change in the stress condition adjoining the excavation. The failure may occur gradually and apparent it as spalling or it may occur rapidly in the form of a rock burst. In either case, the support system design must take into account the modification in the stress condition rather than the 'stand-up' time of the excavation.

#### *4.1.3 Rock quality designation index (RQD)*

It is developed by Deere et al., (1967). Such system provides the quantities estimation of rock mass quality from the drill core logs. RQD is defined as the percentage sum of all intact core pieces having length more than 10 cm in the total length of the core provided that the core should be of NX size (54 mm in diameter). The precise practices for the estimation of the size of core portions and the approximation of Rock Quality Designation Index are summarized as shown in **Figure 2** [11].

In 1982, Plastron suggested that when core is not available and discontinuity traces are visible in surface disclosure or exploratory adits, the RQD may be calculated from the number of discontinuities per unit volume. The suggested relationship is for clay free masses and is given below by Eq. (2).

$$\text{RQD} = \mathbf{115} - \mathbf{3.33 J}\_{\text{v}} \tag{2}$$

the quality of rock mass for selecting of appropriate support and reinforced system. Such classification system not applied generally as compared to other classification systems, but it has its important role in the emergent of other empirical classification schemes. Many investigators advised that for good, reliable and suitable results for planning of excavation more than one rock mass classification systems should be used at initial stage of the project. The significance of the rock structure rating, in the context of this conversation, is to bring forward the idea of assessment of each of the constituents recorded below to calculate a mathematical value of RSR = A + B + C.

*Factor A:* Area Geology: It includes Common evaluation of geological structure

• Geologic structure (immense, marginally faulted/folded, reasonably faulted/

*Factor B:* Geometry of the geological structures: it consists of effect of disjointedness arrangement with consideration to the tunnel alignment on the basis of:

• Rock type Origin (sedimentary, metamorphic and igneous).

folded, extremely faulted/folded).

*Procedure for measurement and calculation of RQD [11].*

*Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*

• Rock Hardness (it means hard, medium, soft and decomposed).

Where,

based on:

**53**

**Figure 2.**

Where,

RQD is the Rock Quality Designation Index,

Jv is the number of all joints per unit length for all joint (discontinuity) sets, so called volumetric joint count.

#### *4.1.4 Rock structure rating*

Wickham et al. (1972) established another quantitatively rock mass classification system termed as Rock Structure Rating (RSR). RSR is used to describe and measure *Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*

advanced classification has been improved by various researchers especially Pacher et al., (1974) and currently formulae the part of the worldwide tunneling attitude so called the New Austrian Tunneling Method (NTAM). The importance of the standup time is to increase in the tunnel width results in a substantial decrease in the period available for the fixing of support. The NATM comprises numerous systems for workable, safe and stable excavation in rock situations where the stand-up time is restricted before collapse occurred. These systems are:

• The use of several small drifts to form a reinforced ring inside which the

As described by Terzaghi (1946), these practices are appropriate to apply in squeezing soft rock mass i.e. shale's, phyllites and mudstones. The practices are also appropriate when tunneling in exceptionally jointed rock, but needs excessive attention to apply these practices to underground excavations designed in hard rocks having dissimilar failure mechanisms. For hard rock excavation support design, it is practical to accept the assumption that the stability of the rock mass adjacent to the underground excavation is not time-dependent. A defined wedge visible in the roof of an excavation will fall as soon as after excavation. This can happen after blasting or during the succeeding scaling process. Early support is demanded do keep such a wedge in place, or to improve the limit of safety preferably before the rock supporting the full wedge is removed. On the other hand, in a highly stressed rock condition, failure will generally be induced by some change in the stress condition adjoining the excavation. The failure may occur gradually and apparent it as spalling or it may occur rapidly in the form of a rock burst. In either case, the support system design must take into account the modification in the

It is developed by Deere et al., (1967). Such system provides the quantities estimation of rock mass quality from the drill core logs. RQD is defined as the percentage sum of all intact core pieces having length more than 10 cm in the total length of the core provided that the core should be of NX size (54 mm in diameter). The precise practices for the estimation of the size of core portions and the approximation of Rock Quality Designation Index are summarized as shown in **Figure 2** [11].

In 1982, Plastron suggested that when core is not available and discontinuity traces are visible in surface disclosure or exploratory adits, the RQD may be calculated from the number of discontinuities per unit volume. The suggested relation-

Jv is the number of all joints per unit length for all joint (discontinuity) sets, so

Wickham et al. (1972) established another quantitatively rock mass classification system termed as Rock Structure Rating (RSR). RSR is used to describe and measure

RQD ¼ 115 � 3*:*33 Jv (2)

stress condition rather than the 'stand-up' time of the excavation.

ship is for clay free masses and is given below by Eq. (2).

RQD is the Rock Quality Designation Index,

*4.1.3 Rock quality designation index (RQD)*

Where,

**52**

called volumetric joint count.

*4.1.4 Rock structure rating*

• The use of small headings and benching

*Slope Engineering*

unpackaged of the tunnel can be mined

**Figure 2.** *Procedure for measurement and calculation of RQD [11].*

the quality of rock mass for selecting of appropriate support and reinforced system. Such classification system not applied generally as compared to other classification systems, but it has its important role in the emergent of other empirical classification schemes. Many investigators advised that for good, reliable and suitable results for planning of excavation more than one rock mass classification systems should be used at initial stage of the project. The significance of the rock structure rating, in the context of this conversation, is to bring forward the idea of assessment of each of the constituents recorded below to calculate a mathematical value of RSR = A + B + C.

Where,

*Factor A:* Area Geology: It includes Common evaluation of geological structure based on:


*Factor B:* Geometry of the geological structures: it consists of effect of disjointedness arrangement with consideration to the tunnel alignment on the basis of:


*Factor C:* it includes influence of groundwater inrush and joint situation on the basis of:


The following tables are used for the calculation of RSR (maximum RSR is 100) [9] (**Tables 2**–**4**).


#### **Table 2.**

*Rock structure rating, parameter a: General area geology [9].*


The RSR value calculated for the above tables are then used for the calculation support system recommendation. The support recommendation chart for the RSR

**Sum of Parameters** *A* **+** *B* **13–44 | 45–75**

Good Fair Poor Good Fair Poor

Anticipated water inflow gpm/1000 ft. or tunnel Joint Condition<sup>a</sup>

*Rock structure rating, parameter C: Groundwater, joint condition [11].*

*Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*

None 22 18 12 26 22 18 Slight, < 200 gpm 19 15 9 23 19 14 Moderate, 200–1000 gpm 15 22 7 21 16 12 Heavy, > 1000 gp 10 8 6 18 14 10

*Joint condition: good = tight or cemented; fair = slightly weathered or altered; poor = severely weathered, altered or*

The rock mass rating system was produced by Biniawski in 1976; it is sometimes

also called geo-mechanics classification system. It was developed taking into account the distinctive case histories in the field of structural designing This classification system was altered in 1974, 1976, 1979 and 1989, because of considering of more contextual analyses identified related to tunnels, mines, chambers, slopes and

foundations [1]. The Geo-mechanics classification system has a widespread

value is given in **Figure 3**.

*RSR support recommendation chart [9].*

**Figure 3.**

**55**

*a*

*open.*

**Table 4.**

*4.1.5 Rock mass rating system (RMR system)*

#### **Table 3.**

*Rock structure rating, parameter B: Joint pattern, direction of drive [9].*


*a Joint condition: good = tight or cemented; fair = slightly weathered or altered; poor = severely weathered, altered or open.*

#### **Table 4.**

• Joint spaces.

*Slope Engineering*

basis of:

[9] (**Tables 2**–**4**).

**Table 2.**

*a*

**54**

**Table 3.**

• Orientation of joints (dip and strike).

• Situation of Joint (poor, fair and good).

*Rock structure rating, parameter a: General area geology [9].*

*Dip: flat: 0–20°; dipping: 20–50°; and vertical: 50–90°.*

*Rock structure rating, parameter B: Joint pattern, direction of drive [9].*

*Factor C:* it includes influence of groundwater inrush and joint situation on the

The following tables are used for the calculation of RSR (maximum RSR is 100)

Igneous 1 2 3 4 Slightly Moderately Intensively Metamorphic 1 2 3 4 Folded or Folded or Folded or Sedimentary 2 3 4 4 Massive Faulted Faulted Faulted Type 1 30 22 15 9 Type 2 27 20 13 8 Type 3 24 18 12 7 Type 4 19 15 10 6

Average joint spacing Flat Dipping Vertical Dipping Vertical Flat Dipping Vertical 1. Very closely jointed, < 2 in 9 11 13 10 12 9 9 7 2. Closely jointed, 2–6 in 13 16 19 15 17 14 14 11 3. Moderately jointed, 6–12 in 23 24 28 19 22 23 23 19 4. Moderate to blocky, 1–2 ft 30 32 36 25 28 30 28 24 5. Blocky to massive, 2–4 ft 36 38 40 33 35 36 24 28 6. Massive, > 4 ft 40 43 45 37 40 40 33 34

**Basic Rock Type Geological Structure**

**Strike <sup>⊥</sup> to Axis Strike ║ to Axis** Direction of Drive Direction of Drive

Dip of Prominent Joints<sup>a</sup> Dip of Prominent Joints

Both With Dip Against Dip Either direction

• Whole rock mass class based previous parameter combined (A and B).

• Quantity of water flow (gallons/minute/1000 feet of tunnel).

**Hard Medium Soft Decomposed**

• Direction of tunnel drive.

*Rock structure rating, parameter C: Groundwater, joint condition [11].*

**Figure 3.** *RSR support recommendation chart [9].*

The RSR value calculated for the above tables are then used for the calculation support system recommendation. The support recommendation chart for the RSR value is given in **Figure 3**.

#### *4.1.5 Rock mass rating system (RMR system)*

The rock mass rating system was produced by Biniawski in 1976; it is sometimes also called geo-mechanics classification system. It was developed taking into account the distinctive case histories in the field of structural designing This classification system was altered in 1974, 1976, 1979 and 1989, because of considering of more contextual analyses identified related to tunnels, mines, chambers, slopes and foundations [1]. The Geo-mechanics classification system has a widespread

application in different rock engineering fields such as mining, hydro power projects, tunneling and hill slope stability (Kumar S. S., 2012). The geo-mechanics classification incorporates the following 6 parameters that are computable in the site and from cores [6]:


While using this classification system, the rock masses are divided into a number of structural regions. Each region is classified independently [12]. These six parameters are being given different rating based on different geological and geotechnical condition as shown in **Table 5**.

Based on the overall rating of RMR calculated form above mentioned parameters support systems are being recommended for the project site. Support recommendation based on RMR value is given in **Table 6**.

#### *4.1.6 Q-system*

This system of rock mass classification was devised by Barton et al., (1979) in Norwegian Geotechnical Institute (NGI), explicitly for the design of tunnel established on 212 case histories. The rock mass classification system is generally used for tunnel design throughout the world and has been used in approximately 1260 various projects and considered as one of the best classification systems for design of tunnels (Kumar N., 2002). The extreme ratings of Q-System shows good quality of rock mass and the lowest ratings designate poor quality of rock mass. The minimum and maximum of Q-index ranges from 0.001 to 10000 on logarithmic scale. According to this classification system Q is the function of six independent parameters as defined by Eq. (3).

$$\mathbf{Q} = \frac{\mathbf{R}\mathbf{Q}\mathbf{D}}{J\mathbf{n}} \times \frac{J\mathbf{r}}{J\mathbf{a}} \times \frac{J\mathbf{w}}{\mathbf{S}RF} \tag{3}$$

**A.** 

**57**

Parameter 1 Strength of intact

Point-load strength index

Unlaxial comp. Strength

Rating

> 2

3 4

 Condition of

Drill core Quality *RQD*

Rating Spacing of

Rating discontinuities

 (see E)

 Very rough

Slightly rough

Slightly rough

Slickensided

 surfaces or Gouge <5 mm thick or

Separation 1–5 mm Continuous

surfaces

surfaces

surfaces

Not

Separation

Separation

<1 mm

continuous

No separation

 Slightly

Highly

weathered

walls

weathered

walls

Unweathered

wall rock

30 None

< 10

10–25

25

20

10 25–125

0

> 125 >0.5

Flowing

0

Rating

> 5

Groundwater

 Inflow per 10 m tunnel

length (Mm)

(Joint water press)/

0

<0.1

 0.1,

 0.2

0.2–0.5

> (Major principal σ)

General conditions

Rating

 Completely

Damp

Wet

Dripping

dry

15

10

7

4

<1 mm

15 90% - 100%

20

> 2 m

20

15

10

 0.6–2. m

 200–600 mm

17

13

 75% - 90%

 50% - 75%

12

7

4 25% - 50%

8 60–200 mm

8

2

 1 <25%

3

< 60 mm

5

Soft gouge >5 mm thick or

Separation >5 mm

Continuous

 0

>250 MPa

 100–250 MPa

 50–100 MPa

25–50 MPa

5–25 MPa 1–5 MPa

<

1 MPa

*Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*

> >10 MPa

> 4–10 MPa

 2–4 MPa

> rock material

**CLASSIFICATION**

**PARAMETERS**

 **AND THEIR RATINGS**\* Range of values

1–2 MPa

For this low range - unlaxial

compressive

 test is

preferred

Where,

*RQD* Rock Quality designation index, *Jn* shows joint set number, *Jr* shows number of joint roughness estimated for the set of joint that is most terrible and dangerous to alignment of tunnel, *Ja* show joint alteration number estimated for the most dangerous and unfavorable set of joint along the alignment of tunnel, *Jw* is joint water condition which shows the water reduction factor, Stress Reduction Factor, SRF is comprised to consider the consequence of in-situ stress condition on the whole quality of Rock. The following comments are offered by Barton et al. (1974) for explaining the meaning of the parameters used to decide the value of Q.

The first quotient *RQD Jn* demonstrating the organization of the rock mass, is a rough measure of the block size.

