Progressive damage and permeability characteristic of gas-bearing coal–rock combination under triaxial cyclic loading

It is crucial to study the damage and failure characteristics of gas-bearing coal–rock combination (GBCRC) structures under cyclic loading for the prevention and management of coal–rock gas composite dynamic disasters. In order to analyze the progressive damage and permeability evolution behavior of GBCRC specimens subjected to triaxial cyclic loading–unloading (TCLU). Acoustic emission (AE)–seepage–damage TCLU tests were performed on GBCRC specimens with various confining pressures and gas pressures using the rock triaxial test system. The findings reveal that improving the confining pressure limits the initiation and propagation of cracks, increasing the progressive damage characteristic stress value of the specimen. Simultaneously, its energy storage limit is improved. The elevated gas pressure hinders the closure of the specimen's internal crack, while simultaneously accelerating the propagation rate of crack, also, the energy storage limit drops as gas pressure increases. The absolute recovery rate of permeability in combination specimens initially declines and thereafter rises progressively. The stress sensitivity of permeability reduces progressively with a rise in the number of stress cycles. The production and spread of cracks are intimately linked to the generation of AE signals, and the evolution of permeability will be impacted by the propagation of cracks. At the same time, as one of the driving forces of crack propagation, energy dissipation behavior also indirectly affects the change of AE signal and permeability. The progressive damage and failure behaviors of GBCRC specimens under TCLU can be fully reflected by the evolution behavior of the AE signal, energy dissipation, and permeability.