Ring Shear Tests On Strength Characteristics Of Landslide Slip Soils In The Upper Jinsha River

Landslides are one of the major geological disasters facing China and the demand for development of new areas(including some bank slopes)is increasing with continuous socio-economic development.There is the problem of safety and stability of slopes during the development of these areas.The mechanism causing a landslide is such that the shear stress on a sliding surface exceeds the shear strength of the surface.A sliding mass of soil is formed by the landslide and plays an important role in its development.The evolution of a landslide is affected,and controlled,by the deformation characteristics of the sliding zone.The rock and soil mechanical characteristics of landslide slip soils,which control the stability of a landslide,are the main factors that affect the stability of such slopes,therefore,this research has important theoretical and practical significance to the study of the engineering properties of landslide slip soils.This study is based on the Upper Jinsha River landslide and entails high-speed,high-pressure,ring-shear simulation and structural analysis.Landslide slips soils from the upper Jinsha River reservoir area are taken as the research object,and the basic properties of the soil samples are tested in a laboratory.Ring-shear tests under normal consolidation and over-consolidated conditions were carried out according to the influencing factors of shearing velocity,normal stress,and preconsolidation pressure.The shear stress-shear displacement characteristics,post-peak softening,strength characteristics,and stiffness are discussed.The ring-shear test is simulated by PFC,the movement of particles is analysed at different normal stresses,and the sheardeformation processes in such samples are simulated.The research entailed the following stages:The basic properties of landslide slip soils were tested: these are mainly composed of silt,and their clay contents are small.The plastic index is 7.7,and the soils were classified as sandy,low-liquid-limit,silts.The shear characteristics of the specimens tested under normal consolidation conditions are analysed.The results show that the fluctuation in the shear stress-shear displacement curves of the specimen varies with normal stress at different shear rates.The increase in normal stress and shear rate will increase the peak strength and residual strength of the specimens,and the shear strength indices varied to differing extents with changes in shear rate.Under high normal stress,the structure of the samples is stable and dense,and the softening of the sample is less severe at larger shear rates.The shear characteristics of overconsolidated specimens are analysed.The shear stress-shear displacement curve of the specimen fluctuated.The combined action of normal stress,consolidation pressure,and shear rate during shear affect the shear characteristics of the specimen.The peak strength and the residual strength under different normal stresses increase with increasing consolidation pressure.The increase of consolidation pressure and shear rate will increase the displacement required for the specimen to mobilise their residual strength.Strain softening of the specimens also occurred,and the magnitude of the applied normal stress during shear affects the post-peak softening of over-consolidated samples.The particle displacement under different normal stresses is analysed by PFC.The results show that the smaller the normal stress,the longer the time needed to reach consolidation stability,and the displacement of particles inside the specimen increases with increasing normal stress.When the normal stress is lower under normal consolidation conditions,more computational steps are needed to reach a stable shear stress,and the shear-band phenomenon of displacement distribution at residual strength is more obvious than that at peak strength.The displacement of specimen particles increases with increasing consolidation pressure in the overconsolidated condition: the shear-band phenomenon of displacement distribution is obvious at high consolidation pressures when the shear is stable.