Ring Shear Test Study On Characteristics Of Loess-bedrock Interface

Among all kinds of geological hazards,landslides are harmful and widely distributed.The study of landslides involves the large shear mechanical characteristics of soil-rock interface.In all kinds of infrastructures and civil buildings,the problem of soil-structure interface is also common.The research on the problem of soil-structure interface has always been one of the most important and key topics in the study of static and dynamic interaction between soil and structure.In this paper,the HJ-1 ring shear tester is used to carry out the test.The ring shear tester is modified briefly.The soil sample above the shear layer and the plexiglass ring below the shear layer simulate the contact surface of rough bedrock.Under different effective normal stress and shear rate,the normal consolidated remolded loess with different moisture content,different dry density and different roughness of the contact surface is tested.The mechanical properties and failure deformation law of the interface between loess foundation and rock under different influence factors are studied.The main conclusions are as follows:(1)The larger the shear rate is,the larger the displacement of the peak shear stress and residual shear strength is,and the shorter the time it takes.Generally speaking,the shear rate has little effect on the peak shear strength and residual strength of the loess-bedrock interface.(2)The shear strength of the interface decreases with the increase of soil water content.The residual cohesion of the interface increases first and then decreases with the increase of soil water content,reaching the maximum near the optimal soil water content.The friction angle in the contact surface decreases with the increase of soil water content,but the effect of water content on it is small.With the increase of water content,the shear failure surface gradually transforms into the failure of shear sliding zone in soil.(3)The influence of dry density on the shear strength of contact surface is very small under larger normal stress.The peak value and residual shear strength of the interface increase with the increase of normal stress under different roughness.When the interface is smooth,the shear strength of the soil interface under different normal stress reaches its peak value,and then the strain softening occurs obviously.When the contact surface is smooth,the shear failure surfaces occur at the loess-bedrock interface,but not in the soil.(4)The shear strength and cohesion of the contact surface increase with the increase ofthe roughness of the contact surface,and the influence of the roughness on the friction angle of the contact surface is small.The effect of roughness on shear strength of contact surface weakens with the increase of roughness.There is a critical value of roughness.When roughness exceeds this critical value,the shear stress and shear displacement curves of the contact surfaces tend to be the same.The cohesion of the contact surfaces with different roughness tends to be the cohesion of the soil sample itself,and the shear failure surface moves to the soil body above the contact surface.