Constraining temporal evolution of shear-induced dilatancy of rock fractures

We combined displacement- and velocity- dependent aperture models to reproduce the transient shear-induced dilatancy of rock fractures in 16 normal stress unloading tests. Our results show that the combined aperture model can well capture the transient aperture evolution during stable sliding induced by normal stress unloading. Slip velocity tends to enhance the modelled aperture increase on smoother fractures at lower normal stresses and higher slip velocities. The dilation factor and characteristic slip distance both decrease with increasing normal stress and surface roughness, indicating reduced contribution of slip velocity to transient shear dilatancy. The dilation angle increases with higher surface roughness, and this increase diminishes at higher normal stresses. These findings highlight the importance of slip velocity in controlling the transient evolution of aperture and permeability of rock fractures. Our study also provides constraints on the constitutive parameters in the combined aperture model for describing transient shear-induced fracture dilatancy.