Study On Shear Mechanical Properties Of Soil-rock Mixture-bedrock Interface

Natural accumulation layer slopes and artificial high fill slopes are widely distributed in southwest China,and landslide geological disasters occur frequently.Landslide disaster has become one of the main disasters affecting the living environment of human beings because of its wide distribution,high frequency,complex destruction mechanism,difficult prediction,destructive,large economic loss,expensive treatment cost and other reasons,which seriously threatens the safety of human life and property.The accretion-bedrock interface exists widely in the accretion slope,which is often discontinuous in nature and has low strength.The contact surface between accumulation layer and bedrock is often the key part and weak link of slope failure,so the contact surface often plays a controlling role in landslide failure,and is the sliding surface of instability failure or the potential sliding surface that cannot be ignored.However,there are some engineering problems that need to be solved urgently,such as difficulty in determining anti-sliding friction of sliding surface and imperfect standard for selecting interface parameters.In this thesis,based on the actual engineering background,the shear characteristics of soil-rock mixture--bedrock interface were studied with the help of indoor large-scale direct simple shear test and numerical simulation,aiming to explore the factors affecting the shear mechanical characteristics of the interface,explore the macro and micro shear mechanical characteristics and deformation characteristics of the interface,and reveal the shear mechanism of the interface.It can provide reference basis and theoretical support for slope stability evaluation and soil-rock mixture filling design.The effects of rock content,size and roughness on the shear characteristics of soilrock mixture interface were studied by using large laboratory direct shear test instrument and self-designed single shear box under low,medium and high normal pressures.The results show that the shear strength can be maximized by the optimum stone content and size of block rock at the soil-rock mixture interface.The shear strength and apparent cohesion(C)of soil-rock mixture interface increase firstly and then decrease with the increase of stone content and size of block rock,and increase continuously with the increase of roughness of bedrock interface.The internal friction Angle(φ)continues to increase with the increase of stone content,while the size of block stone and roughness of bedrock have no obvious effect on the internal friction Angle(φ);The interface between soil-rock mixture and bedrock is a weak potential slip surface,which plays a controlling role in landslide failure.With the increase of rock content,size coefficient of block rock and roughness of bedrock interface,the shear failure surface of samples gradually moves upward,and tends to develop into the interior of soil-rock mixture.The discrete element numerical simulation software was developed twice with FISH language embedded in it,and the irregular blocks were generated and the boundary conditions corresponding to laboratory tests were designed and coded by ourselves.Based on the theory of bonding particle method,the particle breakage simulation was realized by using Cluster particle.Based on laboratory tests,the meso-shear characteristics of soil-rock mixture and bedrock interface were discussed by discrete element numerical simulation,the mesodeformation characteristics of the interface were revealed,and the shear mechanism of the interface was clarified.The results show that the macroscopic mechanical properties and deformation characteristics are determined by the meso-structural characteristics of soil-rock mixture-bedrock interface.The skeleton structure of soil-rock mixture-bedrock interface is composed of the internal skeleton structure of soil-rock mixture and the skeleton structure of contact interface,which jointly bear and transfer the external load.There are concentrated deformation zones in the sample,and the concentrated deformation zones are often connected together to form a rotary shear zone,and the thickness of the rotary shear zone is mainly controlled by the size of the block stone.The shape of shear zone is affected by the existence and size of block stone,and there are "stone-wrapping","stone-enveloping" and "stone-wearing" phenomena.The thickness of the shear zone is related to the maximum particle size of the sample,and the influence range of the shear zone is 1～1.5 times the maximum particle size of the sample.The difference of shear mechanical properties caused by boundary conditions becomes obvious with the increase of normal pressure.Normal pressure can weaken the influence of compaction coefficient on shear characteristics.With the increase of compaction coefficient,the shear strength,internal friction Angle and cohesion gradually increase,but the shear strength increases slowly.