Underground engineering

The following kinds of work are associated with industrial mining needs: 1) trench and open cast mining; 2) construction of embankments, dumps, tailings dumps; 3) construction clearing of ground and building sites; 4) tunnelling, sinking of shafts and corridors; 5) construction of underground industrial structures (coolers, gas storage, etc.); 6) construction of prospecting and production oil and gas wells.

Sites for the mining industry depend mainly on the location of the mineral deposits. Therefore the problem for the engineering-geocryological studies is the rather limited choice of sites for construction and installations. Within the areas of the location of the mineral deposits, the existing geocryological conditions are assessed, forecasts of their change in connection with construction and operations and the development of the mineral deposits are drawn up, with a plan of measures for control of the permafrost processes.

Trench and open cast mining

This is usually carried out in two ways: explosive and mechanical. The latter applies to 30% of the frozen ground under development in Russia. The main difficulty connected with mechanical mining is the resistance of frozen ground to cutting. This characteristic depends on composition, ice content and temperature of the frozen ground (Fig. 17.10). When the method of mechanical mining is selected it should be taken into account that frozen ground has its lowest resistance at discontinuities. Therefore it is profitable to use the procedure of mining based on ground spalling. When mechanical characteristics of frozen grounds are determined, the values of their instantaneous strength are used. Mechanical mining is used as a rule within areas of fine-grained soils. Gravel-pebble rudaceous materials are mined either with explosives or by using the prethawing method.

Storage of mine wastes

This occurs in refuse dumps, rock spoil heaps, tailing dumps (tailings is the term denoting waste from enrichment - loose material composed of various size fractions of crushed minerals) and is a problem of great concern for the mining industry. As tailings represent a fluidified mass saturated with chemical reagents of enrichment, the construction of dikes is the biggest challenge in the course of construction of tailings heaps. Heaps are designed with preservation of a frozen base or with thawing of the soil. In the latter case measures should be taken to prevent seepage of wastes through the dike or through the base. The problem of stability of heaps arises with waste from mines, open cuts, trenches in tailings etc. The height of the heaps of some mining plants reaches a few hundred metres. Thus there exist waste heaps up to 100 m in height in the city of Norilsk. Stability of the heaps depends substantially on the varying temperature of the heap's material throughout a year. It is necessary to know the strength properties of materials making up the slopes (frozen or thawed) and the temperature regime to calculate the slope stability. The stability of heaps, pits, and trench walls (the safe angle of slope and critical mass of the heap) is calculated on the basis of the strength characteristics (angle of internal friction, cohesion, etc.) of the materials, obtained in the course of investigations.

Open cast placer mining

This involves disposal of overburden (peats), with mining and flushing of ore bearing ground (sands). Placer deposits are represented as a rule k MPa

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