Experimental investigation on the pore structure and Water Inrush Evolution Law of weakly cemented fault fracture zone with different filling gradations

Abstract Water and mud inrush caused by fault is a geological disaster characterized by high frequency and huge destructiveness. It is important to study the evolutionary laws of water inrush in fault fracture zones with various filling types. The effect of filling gradation on the mesoscopic structure and seepage characteristics of fault fracture zones was investigated. The law of water inrush evolution and water inrush characteristics of fault-fractured zones with different filling gradations and strong zoning filling characteristics were studied. The results showed that for the larger Talbot gradation indices, the mass of water inrush and the fractal dimension of the lost particles were larger, the peak water pressure and the mass of the lost particles were smaller, and the duration of the initial impermeability stage was shorter for the same loading water pressure. For the fault fracture zones with strong zoning filling characteristics, the peak water pressure, the mass of water surges, and the mass of lost particles were larger, the fractal dimension of the lost particles was smaller, and the duration of the initial impermeability stage was shorter for the fracture zones with larger filling gradation were used as the initial impermeability zones. Furthermore, with larger filling gradation, we observed a greater proportion of large pores, a larger equivalent throat radius, higher pore connectivity, and coordination numbers. Filling gradation and confining pressure greatly affected the permeability of the fault. The permeability decreased by 98.71% when the Talbot gradation indices decreased from 1.25 to 0.6, and decreased by 58.4% when the confining pressure increased from 5 MPa to 15 MPa.