Dynamically induced gouge degradation and implications for fault instability

When a gouge-filled rock discontinuity is subjected to dynamic perturbations, the intrinsic and extrinsic factors, such as gouge properties and loading environments, make its dynamic response extremely complex. Under various loading/unloading conditions, such as stress wave incidence and normal stress unloading, stress drop is a common phenomenon that can be observed with other features in experimental, numerical, and field works. When gouge contacts are approaching to a critical stress state for the shear failure, gouge damage and contact detachment occur accompanied by stress drop and energy relaxation. The stress drop associated with gouge degradation could be a reliable feature to make induced geological hazards interpretable and predictable. It also shows that the reduction of normal and shear stresses is a reasonable explanation of fault instability induced by nearby tunnel excavation.