Recovery of strength along shear surfaces in clay soils

The residual shear strength as operative strength along the shear surface is commonly used for analyzing the stability of reactivated landslides. On this base, it is not possible to have brittle failure or progressive failure mechanisms. In fact, these kinds of phenomena claim for a recovery of strength along the shear surface, which is due to ageing effects during the quiescence time. Several tests on clay samples were performed using Bromhead ring shear apparatus to verify the presence of shear strength recovery. Tests showed that recovery of strength are present along the shear surface. Moreover, they proved the stress-stain behavior is characterized by a brittle failure after that the strength, along the shear surface, falls again to the residual value.