Study on the Deformation and Infiltration Law of Raw Coal Under In-Situ Stress and Gas Pressure

The coupling environment of in-situ stress and gas pressure is among the important factors that can cause coal and gas outbursts and other disasters. Here, an investigation into the deformation and seepage characteristics of raw coal under the coupling environment of in-situ stress and gas pressure was conducted in a laboratory setting, considering the geological conditions of the in-situ stress and gas pressure of the 2+3# coal seam in the Shanmushu Coal Mine. The results show that: Forcing related to gas pressure, in-situ stress, axial strain, radial strain, and deviatoric stress exhibit a linear response in the process of loading axial stress. Poisson’s ratio satisfies a quadratic function with increased deviatoric stress, and the permeability and deviatoric stress satisfy an ExpDec1 function. The linear relationship between axial strain, radial strain, and deviatoric stress is satisfied in the process of loading confining pressure, and the Poisson’s ratio of coal samples increases with the decreased deviatoric stress, as given by an ExpDec1 function. Before reaching the peak strength, the axial strain and deviatoric stress have a linear relationship while simultaneously loading axial stress and unloading confining pressure, and the radial strain and deviatoric stress are related by a quadratic function relationship. The Poisson’s ratio decreases with increasing deviatoric stress, and the elastic modulus increases with the deviatoric stress consistent with an ExpDec1 function. In the subsequent loading and unloading process, the permeability is almost zero before the residual strength appears after failure, and rapidly increases after the residual strength appears.