Experimental and Numerical Investigations of the Dynamic Permeability Evolution of a Fracture in Granite During Shearing Under Different Normal Stress Conditions

The dynamic permeability evolution of a fracture is a key scientific problem for fluid flows in rock masses within engineering systems. Understanding the dynamic permeability evolution and its mechanism is conducive to design and operation engineering. The dynamic permeability evolution of a rough granite fracture was revealed by laboratory experiments and numerical models. The permeability evolution of six fractured samples with rough fractures were monitored under 1.9–20 MPa effective normal stresses. The results show that the shearing process significantly affects the permeability and that the variation trend of the permeability depends on the magnitude of the effective normal stress. Under effective normal stresses of 1.9–5 MPa, the permeability is first significantly enhanced and then decreased by shearing. When effective normal stresses of more than 5 MPa are applied, the permeability only shows a decreasing trend. A high effective normal stress not only limits the dilatancy of a fracture but also enhances the formation of fault gouges. The mechanism of the dynamic permeability evolution was revealed by numerical simulations based on the discrete element method. The shearing mechanism includes the sliding mechanism and shearing mechanism. Under a low normal stress, first, the sliding mechanism is dominant and decreases the contact area, which is conducive to establishing a flow channel and increases the permeability. Then, the shearing mechanism becomes increasingly impactful, causing the contact area to increase and the permeability to decrease. Under a high normal stress, the sliding and shearing mechanisms are always engaged, which generates many wear products and reduces the permeability.