Kinetic Theory of the Fracture of the Coal (Rock) Edge by the Gas-Filled Cracks. Instantaneous Loading-Out
The kinetic theory of the fracture of brittle materials is applied to the study of undercritical and critical growths of cracks in gas-filled rocks. In this type of the materials, the gas filtration from the environment to the cavity of a growing crack plays an important role. The proper account for this factor combined with the dynamics of the stressed state of the bed allows the estimation of the rate of growth of the main crack on the assumption of the Griffith criterion validity. It is found that, immediately after the instantaneous loading-out of the bed in the course of excavation, the cracks of certain size and orientation are exploded with the succeeding growth dependent on the gas entry into the cracks. The time of the filtration growth of the cracks has been estimated. The intervals of the control parameters (formational gas pressure, crack size, overburden pressure, surface energy of coal/rock, modulus of elasticity), where the spontaneous fracture of the bed becomes possible, have been found. The results open a way to the forecast of instantaneous outbursts of coal, rock, and gas.
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