This study investigated the impact of mechanical disturbance and gas deterioration on the coal seam gas seepage. Using a triaxial servo seepage device, we tested cycled pore pressure under varying stress conditions. The results informed that a new permeability model that integrates both the mechanical behavior of coal and gas deterioration of coal and rock was established. The results show that (1) the axial, radial, and volumetric strains of coal and rock show a decreasing trend in the pore pressure increase stage, and the three strain trends in the pore pressure reduction stage are opposite. (2) The axial pressure and confining pressure are constant, and the permeability changes in the process of increasing and decreasing pore pressure. With the change of axial pressure and confining pressure, the permeability gradient is larger when the pore pressure is smaller. (3) On the basis of the new pore pressure increase stage permeability model, the correction factor L was further introduced to establish the pore pressure reduction stage permeability model, so as to verify the accuracy of the model and characterize the permeability evolution characteristics under different pore pressures. (4) In the whole process of pore pressure rising and falling, the elastic modulus and strength of coal and rock are damaged to a certain extent and cannot be recovered. (5) The sensitivity coefficient a of the control correction function L(p) is related to gas desorption, and its value affects the slope of the permeability curve with pore pressure. The value of coefficient b affects the magnitude of permeability, and when the pore pressure is constant, the permeability increases with the increase of coefficient b.
Ren et al. (Wed,) studied this question.