Suction and rate-dependent behaviour of a shear-zone soil from a landslide in a gently-inclined mudstone-sandstone sequence in the Sichuan basin, China

Bedding-controlled landslides in alternated mudstone and sandstone beds in cataclinal slopes are common in the Sichuan basin and in the Three Gorges area in China. They are characterised by very gentle dip angles of the beds (<10°), and usually exhibit slow creep movements throughout the year. However, during the rainy season, they can have sudden accelerations and undergo large displacements. In this work, the influence of saturation degree, displacement rate and stress state on the shear strength of the shear-zone soil was investigated. The results of the displacement-controlled ring-shear tests show a rate-weakening behaviour even at low rates of displacement. Dually, the shear-controlled tests show that the displacement rate can increase dramatically in response to a slight increase of the shear stress. The threshold stress that triggers large displacement is equal to the rate-dependent residual shear strength of the soil.