Energy evolution laws and acoustic emission damage characteristics of coal-rock combinations with different lateral unloading rates

In deep coal mining, excavation-induced lateral stress unloading can trigger rapid stress redistribution and energy release in coal-rock combination, resulting in dynamic hazards such as rock bursts. However, the rate-dependent damage mechanism and energy evolution characteristics of coal-rock combination under different unloading conditions remain insufficiently understood. In this study, triaxial unloading tests with constant axial stress were conducted under four confining pressure unloading rates (0.02, 0.06, 0.10, and 0.14 MPa/s) to investigate the coupled evolution of mechanical response, energy conversion, and acoustic emission (AE) characteristics. The results demonstrate that the unloading rate plays a critical role in controlling the instability and failure behavior of coal-rock combination. Elastic energy is primarily accumulated during the loading and constant axial stress stages, whereas unloading-induced instability is dominated by rapid energy release and dissipation. Increasing the unloading rate accelerates damage accumulation, reduces the energy storage capacity, and promotes more intense AE activity, indicating a transition from progressive damage to abrupt brittle failure. The coupling analysis of mechanical behavior, energy evolution, and AE responses reveals the rate-dependent failure mechanism of coal-rock combination under lateral stress unloading. This study provides new insights into the interaction between unloading rate, energy release, and fracture evolution, and offers theoretical support for instability prediction and mitigation of dynamic hazards in deep coal mining.