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.
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