The principal object of study in rock mechanics is the rock bed and the processes taking place in it during the extraction of minerals. When a bed of rock is worked, the support for the overlying strata is removed from a certain area. This introduces a disturbance into the gravitational and tectonic stress fields existing in the bed and disrupts the equilibrium in the intact strata. Passing into a new state of equilibrium, the rocks adjacent to the workings are deformed, leading to a redistribution of stresses and strains in the bed and particularly in the vicinity of the exposed surfaces~ This picture of variation of the stressed state of rock bed being worked is commonly known and confirmed by in situ and laboratory data. Of special importance for the practice of mining is the concentration of stresses and dislocations in the '!disturbed" zone produced by the mining process.Several hypotheses on the shape and size of the working influence zone have been maintained for a long time in rock mechanics. These include the arch hypothesis [I], the friable medium hypothesis [2], and hypotheses based on the principles of civil engineering mechanics and strength of materials [3,4].

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In the mines of the principal coal basins of the USSR and other countries, numerous instances have been recorded of the destruction of support systems in development workings and stopes, their collapse, destruction of coal pillars, rock bumps, and sudden outbursts of coal and gas during collapse of large roof blocks.Studies in the past few years have shown that, for instance, in the mines of Donets Basin 80% of sudden coal and gas outbursts occur on seams with monolithic rock roofs --made of strong sandstone and sandy schist --as a result of roof sagging.The roof rocks, transferring enormous pressure to the edge of the coal seam, decrease the porosity and gas permeability of the seam which leads to a decreased degassing of the seam being worked.* Various methods for lowering the stresses in the coal mass in the support zone are known at present which are concerned with decreasing the overhang of the console coal bench.Preliminary torpedoing of the roof rocks seems to be the most effective technique.It permits decreasing the overall pressure on the coal bed, enhancing degassing, and lowering the bed stresses.There can be no doubt that the lowering coal seam porosity and hampered degassing due to the overhang of a large rock mass is only one aspect of the bed's overstress.The maximum stress concentrations recordedin the principal coal basins in the USSR lie within the range of 2 to 3. I~ the zone of support pressure these values usually serve as input data for calculations of support system elements; these concentration factors are also used in evaluating the carrying capacity of a coal pillar.A roof collapse is of course, a dynamic phenomenon.However, this fact is not taken into account in the current calculation techniques~ Thepractical consequences of this failure include unexpected destruction of pillars, support damage, etc., even though, when calculated for static conditions, the elements of the system would appear sufficient for the partitular situation.Paucity of studies on the dynamics of processes in a rock mass calls for developing new explorative approaches since these are processes that may be crucial for survival of support systems and coal pillars under certain combinations of mining and geological factors.Thus far, it is impossible to predict the dynamic o~erstresses likely to be sustained by the support systems of a development working or the edge of a coal seam since no adequately substantiated empirical data are available at this moment.Analytical calculations of the relative variations of stresses in the support zone during a rock mass collapse are scant and, for the most part, based on unconfirmed hypotheses.In operational conditions, it is difficult tO evaluate the parameters in the support pressure zone during dyn~c action of roof sagging with the commonly used instruments (dynamometers).The duration and velocity of effects is extremely important. The principal cause of a rock bump is believed to be an excess of the velocity of the mass edge loading over that of stress relaxation in it. % The...