Mechanical-permeability characteristics of composite coal rock under different gas pressures and damage prediction model

Determining the influence of gas pressure on the mechanics, permeability, and energy evolution of gas-bearing composite coal is helpful to better understand the formation process and prevention measures of gasdynamic disasters. In this paper, true triaxial mechanical-permeability tests are carried out on the gas-bearing composite coal rock under different gas pressures, focusing on the influence of gas pressure on the mechanics, permeability, and energy response characteristics of the composite coal rock, and a damage constitutive model based on energy dissipation is established. The results show that increasing the gas pressure decreases the load bearing capacity, strain, pre-peak relative permeability, and deformation capacity of the sample. The greater the gas pressure is, the greater the relative permeability decreases and the greater the post-peak relative permeability increases. The gas pressure has a great influence on the energy of the sample. The elastic strain energy ratio (Ue/U) increases with the increase in gas pressure, and the dissipative energy ratio (Ud/U) decreases with the increase in gas pressure. The coal-rock composite constitutive model based on energy dissipation is in good agreement with the experimental curves.