Study of residual strength of slide zone soil under different ring-shear tests

Slide zone soil of Huangtupo landslide is studied in detail as a typical example in the Three Gorges Reservoir.Three types of shear methods,including single-stage shearing,pre-shearing and multi-stage shearing,are conducted to investigate the residual strength of slide zone soil by employing ring-shear apparatus.It is conducted that the formation of shear band of slide zone soil is relevant with the shear displacement;the residual strength increases with the increasing of effective normal stress.For slip soil sample with a pre-existing shear band,residual shear strength can be soon and easily reached;initial dilatancy phase,contraction phase due to grain migration and constant contraction phase make up shear settlement curves of different ring-shear tests and the changing trend of shear stress in each stage is different.The residual strengths obtained from pre-shearing test and multi-stage test are larger than the actual value;the single stage shearing should be the preferred approach to acquire residual strength of slide zone soil.