Crack propagation mechanisms and stress evolution of floor under dynamic disturbance in deep coal mining

Inrush accidents are easily and frequently caused under high geostress and rising of dynamic disasters which induce crack propagation of rock mass in deep coal mining. So it is important to study the crack propagation mechanisms under dynamic disturbance. According to the elastic theory, the influences of dynamic disturbance of roof on stress of floor are analyzed. The evolution of stress and displacement under dynamic disturbance is simulated. Based on the unloading rock mass mechanics, the propagation mechanisms of cracks in the bottom effect zone under dynamic disturbance and inrush channel development zone under unloading are studied by stages, and the penetration effect of cracks is explored based on the seepage characteristics of rock mass under confined water pressure, and then engineering verifications are carried out. The results show that with the increasing dynamic disturbance intensity, the stress in the bottom effect zone increases nonlinearly. The larger the dynamic disturbance intensity, the higher the starting points of stress unloading, and it easily meets the critical stress of instability propagation of cracks. The dynamic disturbance intensity determines crack propagation and seepage mechanisms, and when the stratum depth of permeability suddenly increased in the inrush channel development zone is larger than the thickness of aquiclude, water inrush of floor will be induced.