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The preparation mechanism for gas-dynamic fracture of outburst-hazardous coal band during an explosive effect on a coal seam is considered. The conditions for crack formation in the zone farthest from the blasthole are studied, as well as simulation of induced cracks filling with methane, which was initially in coal in a dissolved state, and estimation of the start time for crack development due to the pressure of free methane. It is found that, depending on the mechanical and diffusion parameters of coal, the start time for crack development can vary from tens of seconds to many hours. The study results can be useful in developing a theory of explosive effect on a coal seam in a set of measures to reduce the risk of sudden outbursts of coal and gas.

Explosive dynamic impact on coal samples placed in steel storage ampoules is investigated experimentally. The structural features of coal and the nature of its fragmentation are studied via electron microscopy and laser spectrometry for particle size. The different reaction of coal to the impact was determined, depending on the content of gas (methane) in them and their predisposition to dynamic gas destruction. A high share of particles with sizes of around 0.1 microns is observed in disintegrated samples of coal containing methane and prone to dynamic gas destruction, while particles with sizes on the order of several microns formed a substantial fraction of other coal samples. The main phenomenological difference was that storage ampoules with gas-containing coal were partially destroyed during the tests. The possibility of using the results from coal tests to predict hazardous dynamic gas phenomena in mines is considered.

Development of percolating clusters when loading samples of a geomaterial that is hierarchically and stochastically heterogeneous is modeled. The conditions are analyzed for propagation of crack under pressure of methane in the transition phase from a bound state into a free one on the faces of the growing crack in coal.

The mechanism is considered for developing the induced gas-permeability region in the initially impermeable coal seam. Coal shrinkage and rock pressure are the determining factors of the mechanism in question. It is shown that, depending on the geomechanical conditions, both stable development of gas-permeability region and cessation of this process are possible.

538 Coal beds may contain a large amount of gas, mainly methane, most of which is in the adsorbed state in coal [1]. Sometimes during the underground devel� opment of coal beds, quick uncontrolled methane release occurs rapidly (in seconds). The methane released is actively involved in the dynamic crushing of coal into small fractions with a size up to several

1. The methane dissolved in natural coal may participate directly in the dynamic failure of the coal during sudden outbursts.