Study on failure modes and vibration characteristics of multi-layer combined coal mass under impact loading

Abstract Dynamic loading disturbances significantly intensify the damage and failure processes of coal-rock masses, thereby triggering dynamic disasters. However, the failure processes, underlying mechanisms, and vibration response characteristics remain unclear. A self-developed triaxial loading impact testing system was utilized to experimentally investigate the damage-failure behavior and vibration response characteristics of multi-layer composite coal bodies under impact loading. The experimental results show that crack propagation on the coal surface can be divided into four stages: the initial stage, crack initiation stage, propagation stage and stabilization stage. Cracks propagate radially from the center of the coal body toward the surrounding boundaries, with radial cracks developing along the short-axis direction initiating earlier than those along the long-axis direction. Ultimately, surface cracks exhibit ‘O-*’ and ‘*’-shaped failure patterns. After programmed processing of the acceleration signals recorded at each measurement point, the corresponding amplitude and energy characteristics were derived. Among all intrinsic mode functions (IMFs) obtained from signal decomposition, the IMF1 component exhibits the highest energy proportion and plays a dominant role in the impact-induced coal failure. As the number of coal layers increases, the Hilbert marginal spectrum and Hilbert energy spectrum at different measurement points display varying trends. This study elucidates the damage-failure modes, crack evolution laws, and vibration response characteristics of multi-layer combined coal bodies, providing a reference for future investigations into coal-rock dynamic disasters.