N.V. Cherdantsev, Dr. Sci. (Eng.), Chief Research Associate, firstname.lastname@example.org FITs UUKh SO RAN, Kemerovo, Russia
The model of the geomechanical state of the coal-rock massif containing in-seam working driven on the gas-bearing bed is presented. The model is built based on the basic provisions of the mechanics of the deformed rigid body and linear mechanics of fracture. It assumes that the massif is in the conditions of the deformed state and is loaded with the gravitational stress field. It is considered that the characteristics of the strength of the coal seam are less than the characteristics of the strength of the rocks of the hosting massif, but higher than the strength characteristics on their contact. The conditions for the occurence of the inelastic deformations are the adopted criteria for strength of Coulomb-Mor and Mor-Kuznetsov. In this connection, the problem of the stress-strain state of the coal-rock massif is the elastoplastic problem.
Gas pore pressure changes deep into the bed in accordance with the hyperbolic tangent function. At the edge of the bed it is equal to atmospheric pressure, and far from the edge — hydrostatic.
The model assumes that when formulating the boundary conditions at the contact of bed with the lateral rocks, the microcracks with methane pore pressure are oriented vertically. In this connection, in the boundary conditions the horizontal component of the hydrostatic pressure decreases to the value of the methane pore pressure.
By replacing the plastic part of the bed with the normal and tangential stresses acting on the bed contact, the elastoplastic problem is reduced to the boundary-value problem of the theory of elasticity.
To assess the growth of microcracks under the influence of methane pressure the criterion is used, which is obtained within the frame of linear mechanics of fracture.
In the course of the simulation experiment carried out within the frame of the developed model, the graphs of the dependence of the main stresses, methane pore pressure and the indicators of the microcracks growth from the coordinate counted along the contact of the bed with the lateral rocks were plotted.
It is established that taking into account the methane pore pressure in the model insignificantly effects the parameters of the bearing pressure, but gives fundamentally new results with regard to crack growth in comparison with the model, in which the effect of methane pressure is not taken into account.
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