**Abstract**

Grzegorz shaft is the first mine shaft sunk in 21st century in Silesian Coal Basin in USA of ground freezing method. Work carried out by Shaft Sinking Company (PBSz S.A.) is characterized by high level of innovativeness. Geophysical measurements were conducted to find directions of optimization of ground freezing process and its monitoring. Data gathered during research is a starting point for finding directions of optimization of particular fields during Grzegorz shaft sinking, as well as to be used in future similar ventures. Proposed solutions might have bring real improvements for safety and effectiveness of work and also for economic factors. Conducted tests and analysis aim at improvement of monitoring of shape, size and quality of frozen rock mass column in a safe and reliable manner.

**Keywords:** mine shaft, ground freezing, mine safety, geophysics measurements, monitoring methods in mining and civil engineering

## **1. Introduction. Grzegorz shaft: The first shaft in Silesian Coal Basin sunk using ground freezing method in 21st century**

Grzegorz shaft is one of the biggest today's projects in Polish mining industry. Difficult conditions in its geological cross-section forced application of special shaft sinking method, which is ground freezing. This method was in common use in Silesian Coal Basin back in the days, but nowadays it is rarely used, mostly because of a small number of new shafts sunk. This venture was entrusted to Shaft Sinking Company (PBSz S.A.), part of the JSW Group and a leader of highly specialized mining services market in Poland. Company has got 75 years of experience in shaft sinking, including projects in extremely hard conditions, as well as in use of ground freezing method [1].

Application of typical shaft sinking method in case of Grzegorz shaft is impossible because of high rock mass' water accumulation and rock's low soaking resilience. Utilization of different methods, such as rock mass drainage and grouting, were analyzed, but expected low effectiveness effected in their abandonment. As the most effective, safe and reliable, ground freezing method was chosen for purpose of Grzegorz shaft sinking. Its essence is creating a column of frozen ground and it is realized by pumping freezing medium to boreholes. Mine shaft is sunk in such prepared rock mass using traditional methods, such as drill sand blasts. Column of frozen soils and rocks prevents shaft heading from flooding. It can also play a role

of sidewall's support, as frozen rocks and soils are characterized by higher strength than those in natural state. Principles of ground freezing method and solution used for Grzegorz shaft sinking was described in details in following sections [1–3].

Grzegorz shaft was designed as a downcast, man and material shaft. Its inner cross-section is circle with a diameter of 7,5 m. Ordinate of surface level is +258,0 m and its depth is 870,0 m [3].

Shaft sinking is a huge and complicated venture, especially in terms of difficult geological conditions. However, Grzegorz shaft sinking is characterized by high level of innovativeness. One of the biggest innovations is application of the same head frame for both processes of sinking and regular operation of Grzegorz shaft. It is a first such case in Polish coal mining. Up to now, every mine shaft in Polish collieries was sunk using head frame of special construction, which were then disassembled and final head frame was built. But innovative way of thinking applies also to other areas of design and construction of Grzegorz shaft. Geophysical survey was conducted to determine new directions of optimization for processes of shaft sinking in a frozen rock mass and monitoring of ground freezing process [3].

#### **2. Ground freezing method**

The essence of special method of shaft sinking, which is ground freezing method is freezing of aquifers and then shaft sinking in frozen rock mass, using traditional methods, such as drills and blasts. It was primarily used in 1862 in England. Rock mass was frozen by freezing medium flow through a spiral pipe placed on a surface of quicksand's layer. In 1883 in Archibald mine, located near Schneidlingen, rock mass was frozen using technology similar to the one used nowadays. In Siberia's gold mines in 1940's shaft sinking method utilizing natural ground freezing was commonly used. It was then neglected, because of low effectiveness [4].

Low temperatures needed for freezing of soils and rocks around sunk shaft are obtained by heat of freezing medium transition from liquid to gas. The most common freezing medium is ammonia NH3. Freezing boreholes are drilled around contour of the shaft. Distance between them is 0,9 to 1,2 m. They are equipped with casing pipe, so called freezing pipes, with diameter between 100 and 160 mm and pipes with diameter of 25–45 mm inside the freezing pipes. They are called inlet or inflow pipes, and are shorter than borehole depth (pipe do not reach borehole's bottom). Freezing medium is brought to a freezing ring on the surface, where it is distributed to freezing boreholes. It is then pumped into the boreholes through inflow pipes. Freezing medium flows between casing and inlet pipes, cooling rocks and soils via conduction. Constant rock mass cooling leads to freezing of water inside soils and rocks. Column of frozen ground develops around the freezing borehole. Such columns around numerous boreholes combine with each other, which effects in development of one cylinder of frozen ground around the outline of the shaft. This column of frozen soils and rocks prevents shaft heading from flooding and resists pressure of water and rock mass [4–11].

Various liquids can be pumped into freezing boreholes, such as aqueous solutions of calcium, sodium or magnesium chloride. All of them are characterized by low freezing temperature. The role of refrigerant is heat carrying, transferring it from rock mass to evaporator. It flows through freezing pipes in boreholes, collector and evaporator, where it is cooled down [4].

Strength of frozen rock or soil is higher than in natural state. The highest compressive strength characterizes frozen gravel and coarse-grained sand. Fine-grained sands and clays have lower compressive strength. Strength of frozen ground is also dependent on ice strength, which is related to ice grains' size and freezing time.

**3**

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking*

As rule of thumb, the faster freezing process the higher ice strength. Time of freezing depends on conductivity of casing pipes, freezing installation effectiveness and

Hydrogeological, geological and engineering conditions were determined on basis of data collected from boreholes G-8 and G-8bis, drilled specifically for this purpose. Stratigraphic profile in axis of the designed Grzegorz shaft consists of:

• **Quaternary formations** between 0,00 and 40,43 m – layers of sands, clay and

• **Tertiary formations** between 40,43 and 114,43 m – layers of slit, clay, aggre-

• **Triassic formations** between 114,3 and 234,93 m – layers of dolomite, lime-

• **Carboniferous formations** below 234,93 m – layers of sandstone, claystone

Four aquifers with sixteen water bearing horizons are located in Grzegorz shaft profile. In quaternary formations there are two water bearing horizons, both with confined water table. It is fed by rainwater. Reservoir rocks are clays, sands and aggregates. Tertiary aquifer consists of single water bearing horizon with confined water table. It is also fed by rainwater. Reservoir rock is a limestone. Three water bearing horizons occur in Triassic aquifer, all of them with confined water table, also fed by rainwater. Reservoir rocks are dolomite, limestone, mudstone and sandstone. There are ten water bearing horizons in Carboniferous aquifer. Reservoir rock for all of them is sandstone. All horizons are also characterized by confined water

Estimated water infiltration to the shaft heading from different aquifers varies

According to observations made during drilling G-8bis borehole and laboratory tests of core sample there are seven different geotechnical zones, characterized with

It was found that there are extremely difficult geological conditions in zones I, III, V and VI, caused by low soaking resilience of rocks and high accumulation of water. Shaft sinking in such conditions is impossible without utilization of special methods, because there is a real threat of problems with sidewalls' stability.

/min. Total expected water supply is equal 5,957 m3

/min.

table. There are fed by water infiltrating from upper stratigraphic layers.

Project of ground freezing has to be preceded by precise geological and hydrogeological measurements in the vicinity of designed shaft. In particular, it is important to identify hydrogeological conditions, such as number of aquifers, their

*DOI: http://dx.doi.org/10.5772/intechopen.95885*

depth and range, water pressure and its chemism [4, 8].

amount of heat to transfer [4–7].

**3. Geological conditions**

**3.1 Geological structure**

aggregate;

and hard coal.

between 0,057 to 0,926 m3

**3.3 Engineering conditions**

different geotechnical parameters.

**3.2 Hydrogeological conditions**

gate, claystone and limestone;

stone, clay, sandstone and mudstone;

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking DOI: http://dx.doi.org/10.5772/intechopen.95885*

As rule of thumb, the faster freezing process the higher ice strength. Time of freezing depends on conductivity of casing pipes, freezing installation effectiveness and amount of heat to transfer [4–7].

Project of ground freezing has to be preceded by precise geological and hydrogeological measurements in the vicinity of designed shaft. In particular, it is important to identify hydrogeological conditions, such as number of aquifers, their depth and range, water pressure and its chemism [4, 8].
