The seepage characteristics of rough fractures under cyclic shear loading

The continuous wear and degradation of rough surfaces induced by cyclic shear significantly affects fluid flow patterns within rock fractures. This study explored the seepage behavior of rough fractures during cyclic shear processes using a numerical simulation method that couples ANSYS/LS-DYNA with ANSYS/FLUENT. Initially, cyclic shear tests were performed on rough fracture specimen, and these tests were subsequently replicated in LS-DYNA to generate fracture models at various shear stages. The pore size distribution and contact ratio evolution of the fractures were analyzed, and based on these findings, flow simulations were conducted using FLUENT to solve the Navier–Stokes equation. The simulation results indicate that as shear displacement u increases, the dilatancy effect leads to an increase in fracture aperture, a decrease in vortex distribution, a weakening of fluid flow nonlinearity, and an increase in fracture transmissivity. However, with an increase in the number of cyclic shear cycles N, the fracture aperture decreases, the contact ratio increases, vortex distribution increases, fluid nonlinearity intensifies, and fracture transmissivity decreases. Additionally, during forward and backward cyclic shear processes, fluid flow within the fractures exhibits anisotropy. By calculating the equivalent hydraulic aperture of the fractures and comparing it with results obtained using existing equations, it became evident that considering the contact correction term is essential when evaluating the hydraulic characteristics of rough fractures. This study not only clarifies the impact of cyclic shear on fluid flow behavior in rock fractures but also showcases the potential of numerical simulation in predicting fracture hydraulic characteristics.