Mechanical behavior and acoustic emission characteristic of coal-rock composite with prefabricated hole under compression

In deep coal mining, the stability of coal roadways is critically governed by its immediate roof and floor strata. This study investigated the evolution characteristics of mechanical behaviors of coal-rock composites, aiming to elucidate its failure mechanism. Results demonstrated that, compared to sandy mudstone-coal-sandy mudstone (SCS) composites, the red sandstone-coal-red sandstone (RCR) composites exhibited more pronounced fracturing, greater stress fluctuations, and significantly higher acoustic emission (AE) activities, characterized by markedly higher AE ringing counts. For SCS composites, AE ringing counts surged at the initial stress drop point, and peaked twice near its ultimate failure point. Notably, between these two points, a distinct quiescent phase of AE activities was identified, serving as a precursor for imminent failure. Furthermore, the generation of tensile and shear cracks exhibited both a spatiotemporal concentration and a distinct stage-dependent evolution pattern. Specifically, AE events in SCS composites were concentrated vertically with higher density within the central coal layer, while in RCR composites, the high-energy AE events clustered predominan