Experimental study of impact of shearing velocity and effective normal stress on post-shearing permeability evolution of silica fault gouges

Abstract Fault permeability is an important parameter for understanding the occurrence of natural hazards and evaluation of natural gas and oil reservoirs. In this study, effects of shear velocity on the permeability perpendicular to the shear zone formed after large shear displacements are revealed for silica sand. To this end, ring-shear experiments were performed for four shearing velocities under conditions of high effective normal stress. As observed, post-shear permeability values under effective normal stresses of 1 and 2 MPa demonstrated a reduction of two and one order of magnitude, respectively, along with negative velocity dependence. However, no significant difference in permeability was observed under exceeding 3 MPa. In addition, the shear-zone structure under high shear velocity and higher effective normal stress demonstrated existence of a grain-crushed zone, which closely corresponds to reductions in pore-diameter and grain size. Findings of this study indicate the instability mechanism of landslides related to groundwater movement and facilitate understanding of resource systems controlled by natural faults.