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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.

Contemporary rock mechanics is based on the principals of classical Continuum Mechanics theory. But new experimental results such as “zonal disintegration” around deep openings and “reversible deformations” of highly compressed rock samples cannot be described correctly from this viewpoint. A new approach to rock mechanics mathematical models consists of the application of non-Euclidian modelling to the problem of the description of anomalous experimental results. This leads to the formation of the “Geomechanics of Highly Compressed Rock and Rock Massifs” – a new branch of the existing theory of Geomechanics – in which framework a radical rise in geodynamical phenomena forecasting can be achieved. Principles of the geomechanics of highly compressed rock and rock massifs are discussed in this paper. The effectiveness of the application of non-Euclidian modelling to the anomalous experimental effects observed in research is demonstrated on two hierarchical geomedia block levels such as rock samples and rock massif around underground openings.

Considering features of wave prefracturing (microfailure) of rocks under blasting, the authors put forward a new investigation approach with the use of relations of dynamic elastic stress distribution in rocks and theory of cracks. The obtained relation to estimate prefracturing zone size in relatively solid rocks under confined explosion involves pressure of gases in explosion chamber, rock pressure, crack resistance of rocks, characteristic dimension of natural jointing (presence of defects) and deformation characteristics of rocks. It is shown that dimension of prefracturing zone in rocks depends both on natural and production factors and can differ by a few times.

The authors review water inrushes in mines as a consequence of spontaneous hydrofracturing of surrounding rocks. In the developed hydrofracture model, the fracture grows under the pressure of underground water in the area of reduction in mining-induced stresses. The model includes two criteria of fracture growth—critical extension of rocks at the fracture tip and opening of fracture throughout the length. It is found that spontaneous hydrofracturing is conditioned by natural and induced stresses, hydrostatic pressure of underground water and by mining sequence.

The different-scaled periodicity of the non-uniform spatial distribution of deformations in a rock mass, resulted from its natural hierarchic block structure, is detected by using the Fourier and wavelet analyses. It is established that the block structure of the studied rock mass sections meets the concept on fundamental canonic series of geoblocks in the Earth’s crust.

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.

Microparticle emission upon rock deformation is established experimentally. The results from experiments on the uniaxial compression of samples with a through hole as a stress concentrator with the simultaneous recording of emissions of mineral particles using laser spectrometry are presented. Quantitative estimates of the emission of particles in the size range of 0.3–5.0 μm with respect to the acting stresses are obtained.

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.

This paper presents a model for inelastic deformation of brittle rock in the prelimiting condition in which consideration is given to microcrack dilation. A study was made of the stress state of the rock mass close to an unsecured working of circular cross section. A simpler model for deformation of brittle rock may be constructed in the case when tests are carried out by compression of specimens only with a uniform side load.