Deformation failure mechanism and experimental study of gas-bearing coal rock mass based on percolation mechanism

Aiming at the problem of loose damage caused by gas in high stress environment and taking into account the porous media characteristics of coal and rock mass,the failure deformation mechanism under the influence of stress disturbance of gas-bearing coal and rock mass was studied. Firstly,the concept of gas-bearing coal and rock mass per- colation failure was put forward based on percolation theory,whose essence is a kind of dynamic failure which occurs when the gas is protruded to cause the coal rock to break down. Then,the distribution area of percolation damage was analyzed and the calculation formula of percolation failure probability P¥ was given. The Biot-type constitutive equation and field equation of gas-bearing coal rock mass are deduced by classical mixture theory. The results show that the pore and fracture of gas-bearing coal and rock mass are closely related to permeability coefficient and effective stress. Finally,according to the constitutive equation of gas-bearing coal,the method was applied to the percolation failure zone,and the formula of percolation damage zone radius Rp was obtained. Based on the preparation of the rock speci- men containing gas of three axial compression test,the test results show that with the increase of the pores and fissures of the rock specimen,the specimen elastic modulus and the brittle-ductility critical failure point decrease. At the same time,specimen cohesion and internal friction angle values were reduced in different degrees with the increase of inter- nal gas pore,resulting in increased percolation damage zone radius,and its influence will enhance with the decrease angle of internal friction and cohesion. Finally,with the increase of stress,the pore pressure increases,when the stress continues to increase,the pores and fissures gradually pass through,and the specimens eventually undergo loose fail- ure,that is percolation damage.