Plastic deformation-based constitutive relation of coal damage and permeability model

Coal and gas outburst induced by mining disturbance is one of the main gas dynamic disasters in coal mine production. In order to systematically explore the evolution characteristics of coal damage and the law of gas seepage under mining disturbance, the whole stress strain–seepage experiment under different gas pressures was carried out. The generalized Hooke's law was modified by considering the effects of gas adsorption and thermal expansion, the plastic deformation-based constitutive relation of coal damage was established, and the piecewise permeability model considering the damage was further constructed. The results shown that the coal permeability can be divided into two stages: before and after the peak, taking the sudden change point of permeability as the boundary. The permeability decreases exponentially before the peak and increases sharply after the peak, and the peak compressive strength and elastic modulus decrease with the increase of gas pressure. The evolution law of axial plastic strain and damage of coal has good consistency, and both of them show a trend of little change before the peak and rapid increase after the peak. The damage model and permeability model were verified by using the experiment data under different gas pressures and 50℃, and the theoretical curves were in good agreement with the experiment data, which shows that the new model can better reflect the damage evolution law and gas seepage characteristics in the process of coal damage and the instability under different conditions.