Numerical study on damage response and failure mechanism of gas-containing coal-rock combination under confining pressure effect

• The impacts of confining pressure and gas on coal-rock combination are analyzed. • The meso -damage response and process of the coal-rock combination is studied by DEM . • The failure mechanism of combination under confining pressure effect is determined. The research on mechanics properties and destroy behavior of coal-rock combination is extremely crucial for deep coal mining. However, there are few studies on the gas-containing coal-rock combination under the confining pressure effect, resulting in insufficient comprehension of the failure mechanism of the combination with different confining pressure. In this paper, a discrete element method (DEM) model of combination with stress-gas coupling is established. The related mechanics properties of single coal samples and combination samples under stress-gas coupling are compared and studied, such as axial stress, crack generation and failure mode. The results demonstrate that the coal mass in the coal-rock combination is continuously damaged and compacted during the loading process with different confining pressure. The interfacial effect caused by the circumferential expansion or irregular deformation of coal mass, and the improvement of compression intensity of the compacting coal mass jointly induce damage of the rock mass. The combination with confining pressure 4, 7 and 10 MPa exhibit the macroscopic failure characteristics of coal mass dominant, coal and rock mass together, and rock mass dominant, respectively. Meanwhile, the confining pressure effect also greatly determines the formation of the final failure pattern of combination samples after macroscopic failure.