Modelling of Flow–Shear Coupling Process in Rough Rock Fractures Using Three-Dimensional Finite Volume Approach

A computational code has been developed based on finite-volume method (FVM) to investigate fluid flow-through rough-walled rock fractures during shear processes, considering evolutions of aperture and contact area with shear displacement. In the code, the full 3-D Navier–Stokes equation is solved in a cell-centered collocated variable arrangement and the pressure–velocity coupling is performed using the SIMPLE algorithm. A series of coupled shear-flow tests under constant normal stress of 3 MPa with different shear displacements of 1–10 mm were conducted and their results were compared with numerical simulations results. The comparison shows good agreement between the simulated and measured results. Aperture distribution during shear was evaluated by superimposing the upper and lower fracture surfaces according to the initial aperture and dilation at different shear displacements. The results show that contact area evolution dominates the variations of flow rate as well as flow pattern in a rough fracture. In addition, there is a linear relationship between aperture coefficient of variation and contact area ratio during shear. The simulation results also demonstrate the deviation of velocity profiles from the ideal parabolic form in some regions due to the formation of eddy flows. This behavior may have been caused by the inertial effects, which can be characterized by the Navier–Stokes equation, while some simplified equations such as Reynolds equation or Stokes equation cannot capture these effects.