Study On Dynamic Strength Characteristics And Instability Mechanism Of Outwash Deposit Landslide In Xishan Village,Li County

In early August 2017,the outwash deposit landslide started in Xishan village,Tonghua township,Lixian county,Aba Tibetan and Qiang autonomous prefecture,Sichuan province.So far,no consensus has been reached on the mechanism of instability.Based on the research,this thesis puts forward that it is started under the action of multiple periods of secondary dynamic loads generated by engineering blasting,which is affected by the creep deformation caused by the gravitational potential energy,and the later stage was affected by the interaction of rainfall infiltration and landform to promote the landslide instability.In the process of landslide instability and destruction,two houses were damaged,a village road was built,and some farmland was buried in the middle of the slope,causing certain economic losses and threatening the safety of life and property of residents on both sides of the Wenchuan-Malkang expressway under construction at the foot of the slope and the G317 national road already built.Through the early stage of the research team information collection,field investigation visit many times,Unmanned aerial vehicle?UAV?is taken,find out the basic form and scale,the landslide material composition,structure characteristic,and the landslide deformation and failure characteristics,through the medium indoor dynamic triaxial test to find out the typical water accumulation dynamic strength parameters,including its deformation and failure regularity,dynamic mutual index the relationship analysis,comparing with outwash deposits'dynamic/static strength,eventually based on deeply summarizing the influence factor of the landslide,combined with FLAC^3D to simulate landslide formation mechanism model and qualitative analysis of landslide instability mechanism,concluded as follows:?1?The whole landslide is in an irregular shape,with steep ridge as the boundary at the back edge and gully as the boundary at the left and right sides,and the accumulation boundary at the front edge visible.According to the main sliding direction,it is divided into two sections,the upper?149°?and the lower?127°?,with an oblique length of 650m,an average width of 90m,an area of 26,600 m² and a total cubic volume of 478,000 m³.The structure of the landslide body is relatively broken,and cracks develop in the slope.The slip zone runs through the soft structure surface at the interface between the silty clay layer,and the breccia soil layer,and is cut out at the air surface at the interface of the steep slope.?2?Based on the analysis of the results of many detailed field investigations and monitoring data,the landslide has shown three typical deformation failure characteristics in the three months after the start of the landslide,namely,seismic crack damage,continuous deformation development,and slope collapse and disintegration,which correspond to three stages of slope structure deterioration,accelerated deformation and gradually stable deformation.?3?the results of dynamic triaxial test show that outwash deposits is more prone to shear failure under dynamic load,and breccia soil are more prone to failure than silty clay.Breccia soil is prone to failure at low confining pressure and only some samples fail at high confining pressure.The dynamic modulus and dynamic strain of outwash deposits have a logarithmic function relation,the damping of brecciated soil is smaller and fluctuates greatly compared with silty clay,and the damping of brecciated soil has a wide range of oscillation.?4?The main factors affecting the landslide include the multi-stage concentrated dynamic load,rainfall,and geological environment caused by the blasting of the tunnel at the foot of the slope.Dynamic load damages the original structure of landslide,damages the soil structure and produces tensile cracks.The rainfall infiltration crack increases the gravitational potential energy of the landslide and reduces the shear strength of the soil.The complex landform is the main internal cause of landslide instability.?5?The simulation results of FLAC^3D software show that under dynamic load,the trailing edge of the landslide begins to suffer from small-scale tensile failure,and the sliding belt undergoes shear failure along with the weak structure from the trailing edge.The displacement and shear strain changes are not obvious temporarily and are still in the start-up stage.As the landslide starts to creep under the action of gravitational potential energy and rainwater infiltration cracks,the plastic failure of soil is accelerated by converting the gravitational potential energy into dynamic potential energy while reducing the shear strength of soil.There is an obvious plastic deformation failure zone in the landslide,which runs through the whole sliding surface along the soft clamp,and promotes the failure of the whole landslide.?6?The landslide shows the deformation and failure mode of Creep-Tension Crack-Shear Break.In the early stage,the secondary dynamic load destroys the soil structure,and tensile cracks appear at the rear edge,which marks the start of the landslide and creep under the action of gravitational potential energy.In the middle period,rainfall infiltration increases the moisture content of the weak interlayer,reduces the shear strength of the soil in the sliding belt,increases the load effect of the sliding body and gradually converts it into the dynamic potential energy.Due to Shear Effect,the leading edge of landslide accumulation developed into Toe Shape along the gully,and the movement direction and distribution area increased obviously.