Failure characteristics and mechanism of coal under the coupling between different confining pressures and disturbance loading

Deep coal is highly susceptible to dynamic disasters such as rock bursts under the influence of mining. Further exploration of the damage mechanism of coal specimens subjected to cyclic disturbance under different stress conditions is necessary. This study conducted cyclic disturbance failure experiments with coal specimens under different confining pressures, and the acoustic emission (AE) and electromagnetic radiation (EMR) signals were collected. The results show that, under the coupling effect of high stress and disturbance loading, the higher the confining pressure, the greater the disturbance the coal specimen can bear, and most of the specimens are fractured in the loading and unloading stage. Compared with uniaxial loading, the EMR response of coal specimens in the compaction stage is weakened after applying confining pressure. It can also be observed that the greater the confining pressure, the more intense the AE and EMR changes during the rupture of the coal specimen. The confining pressure is positively correlated with the degree of coal fragmentation. This correlation implies that the larger the confining pressure, the smaller the fractal dimension of coal fragments. The intrinsic driving mechanism of coal fracturing was analyzed from an energy perspective. The effects of confining pressure and disturbance loading and unloading cause coal specimens to accumulate more elastic strain energy before fracture, decreasing the post-peak fracture energy and residual strain energy. This study has theoretical reference in preventing and controlling dynamic disasters induced by a disturbance in deep coal mining.