Thixotropy Induced Variation in Viscous Resistance of Experimentally Sheared Mudstone Granules

The determination of residual resistance of the landslide sliding surface is of paramount importance in landslide mechanics, as sliding surface controls the stress drop, the mechanical work. In present study, by the use of the ring shear tests, variation of the residual strength of the samples with coarse and fine mudstone particles were s tudied both in dry and saturated s ituation. Not evident variation of residual s trength was observed for the dry coarse particle samples as well as the saturated samples with the fine particles. For the saturated samples with coarse particles, the residual friction coefficient dropped from 0.6 to around 0.1 when the shear velocity speeded up to a certain value (about 2mm/s) and then the residual strength recovered to the original value when the shear velocity decreased to a certain value. These cycles of acceleration with residual strength dropping and deceleration with residual strength recover can continue for a long shear displacement. These variation of the residual strength can also happen with constant shear rate. A conceptual model has been raised to explain this phenomenon by thixotropy of the slurry, resulting from the comminution of grains in the shear zone.