Mine Shock

a cleavage fracture of the most highly stressed part of a layer of coal or rock adjacent to a mining excavation. It occurs when the rate of change in the stressed state in this part exceeds the maximum rate of relaxation of stresses in it as a result of plastic deformations. The elastic energy of the coal layer at the center of the shock and the energy of the surrounding rocks participate in the mine shock. The shock is accompanied by a sharp noise, a blowout of coal, the formation of dust and an air wave, and destruction of the shaft lining, machinery, and equipment. Elastic expansion of the rock adjacent to the center of the collapse generates seismic waves which, in the case of a mine shock of great force, spread for dozens or hundreds of kilometers.

Mine shocks are subdivided by their force into bursts, jolts, microshocks, and mine shocks proper. Combating mine shocks is a pressing problem for many ore and coal regions of the world. Mine shock usually occurs in shafts where work is going on at depths greater than 200–400 m. It may be averted by reducing rock pressure on the coal layer (preliminary working of safe neighboring layers, conducting work without pillars of coal, reducing hanging rock, and so on) and by reducing the ability of the layer to accumulate elastic energy (loosening with underground explosions or forcing water into the layer).