Abstract: The dynamic evolution of fracture permeability is a critical issue in understanding the hydraulic characteristics of engineering rock masses. Investigating the dynamic evolution mechanisms of rock mass permeability is crucial for engineering design and operation, as it clarifies the factors influencing this process. Using the discrete element method and finite element method, this study establishes a numerical simulation framework for shear seepage in rough granite fractures to investigate the dynamic evolution of fracture aperture and permeability under varying confining pressures during shearing. The study reveals the dynamic evolution law of fracture permeability in rough granite during the shear process. Numerical simulations were conducted to analyze the shear and seepage processes of rough fracture samples under confining pressures ranging from 1.9 to 20.0 MPa, monitoring the evolution of fracture aperture and permeability. The numerical simulation results align with experimental observations, indicating that shear processes and confining pressure conditions significantly influence permeability evolution. Additionally, the magnitude of confining pressure determines the trend of permeability changes. Under confining pressures of 1.9–10.0 MPa, permeability initially increases significantly but decreases after shearing. When confining pressure exceeds 10.0 MPa, fracture permeability exhibits a downward trend throughout. Shear numerical simulations reveal that high confining pressures restrict fracture shear expansion, promote rock debris formation, and reduce the fracture’s water-carrying capacity. This study systematically proposes an equivalent aperture correction coefficient based on the Barton formula, provides a physically meaningful permeability calculation method, and establishes a standard evolution equation linking fracture equivalent aperture and effective confining pressure. These formulations enable accurate predictions of initial, peak, and minimum equivalent apertures under varying confining pressures and facilitate permeability calculations. The shear seepage numerical simulation method offers an effective approach to elucidate the dynamic evolution mechanisms of fracture permeability.

Key words: fracture, confining pressure, permeability, aperture, numerical simulation