**3. Geological conditions**

#### **3.1 Geological structure**

*Computational Optimization Techniques and Applications*

and its depth is 870,0 m [3].

**2. Ground freezing method**

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

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].

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

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

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.

and resists pressure of water and rock mass [4–11].

and evaporator, where it is cooled down [4].

**2**

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:


#### **3.2 Hydrogeological conditions**

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

Estimated water infiltration to the shaft heading from different aquifers varies between 0,057 to 0,926 m3 /min. Total expected water supply is equal 5,957 m3 /min.

#### **3.3 Engineering conditions**

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

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. Occurrence of these geotechnical zones enforced utilization of ground freezing method for Grzegorz shaft sinking.
