Mechanism of Floor Water Inrush Induced by Fault Activation under Earthquake Conditions

For the water inrush of faults in coal mining, this paper studies the mechanism of floor water inrush induced by fault activation under earthquake conditions. First, the mechanical model of fault activation under earthquake conditions is constructed. The critical fracture water pressure in the fault zone is derived using the quasi-static method and rock shear failure criterion. The fault activation criterion is proposed, and the fault activation conditions are analyzed based on fault formation mechanisms. Second, the forming process of the floor water-conducting channel (key route of fault water inrush) is explained through connected fractures. The critical water pressure of failure is derived for the water-resisting layer using the quasi-static and limit-equilibrium methods. The mechanical criterion for coal floor water inrush is presented. Third, fault activation and floor water inrush affected by seismic intensity, fault dip angle, coal seam depth, and other factors are analyzed. Finally, the proposed computation model is verified through engineering case analysis and numerical simulation. The results show that: (1) Fault activation occurs when the fracture water pressure of exceeds the critical water pressure required for fault activation. When the water pressure of the water-bearing stratum is more than the critical water pressure of floor water inrush, water inrush from the coal floor will occur. (2) The critical water pressures for both fault activation and floor water inrush decrease nonlinearly with increasing seismic intensity, while they increase linearly with the depth of the coal seam. (3) Under earthquake action, the fault with a dip angle between 50° and 55° is most prone to be activated, and the fault with a small dip angle is more likely to cause floor water inrush. (4) With the enhancement of the mechanical properties of the fault, the critical water pressure required for fault activation and floor water inrush increases gradually.