Statistical Damage Constitutive Model of Gas-Bearing Coal with Consideration to Crack Deformation

Coal is a complex porous medium. When gas exists in the coal body, the fissure structure of coal and the occurrence of gas adsorption make the stress state of gas-bearing coal different from that of ordinary coal. Therefore, the stress state of gas-bearing coal cannot be accurately described by the Terzaghi effective stress, which ignores the effects of crack deformation and methane. To improve the accuracy of gas-bearing coal analysis, this study considered the corrosive effect of free gas and adsorbed gas and the crack closure effect to establish a novel statistical damage constitutive model with consideration to the combined effects of free gas, adsorbed gas, and coal cracking. The established model was used to elucidate the effects of gas-bearing coal on the coal's mechanical deformation and damage characteristics under different stress conditions. The model was validated through full stress-strain experiments on gas-bearing coal under different axial pressure and gas pressure. The results obtained by the proposed statistical damage constitutive model can better describe the stress state of the gas-bearing coal, particularly in the initial stage of void compaction, and are in good agreement with the experimental data. The proposed model provides the theoretical foundation for future studies on the characteristic mechanism of gas-bearing coal.