Abstract: To investigate the mechanisms of floor failure and further induced risks of water inrush by the strong unloading effect of high-stress rock mass in deep coal mining, the influence of unloading on floor disturbance and failure was analysed with the theory of unloading rock mass mechanics. It calculated the strong disturbance characteristics of floor rock mass unloading damage in deep coal mining by using the discrete element method (DEM). Based on triaxial unloading tests and the concept of damage factor, we obtained the relationship between unloading percentage and damage factor, determined the propagation and failure condition of rock mass, and achieved the unloading disturbance partition of floor. Then the disturbance hazard of floor rock mass unloading damage and failure in deep coal mining were further studied. The results show that with mining depth increasing, both unloading starting point and unloading stress of floor are increased, but the unloading percentage is reduced, in which the lower unloading percentage causes damage severely in deep coal mining. When the unloading percentage of rock mass is greater, its unloading rate and displacement and the permeability coefficient become higher, which easily induces floor rock mass instability propagation. When the dip angle of crack and the ratio of horizontal stress and vertical stress are low, it easily reaches the propagation and failure conditions of floor rock mass unloading.

Key words: unloading damage, strong disturbance, crack propagation, floor water inrush, deep coal mining