Study On The Formation And Evolution Mechanism Of Landslide In Caishu Of Xide County

Over the years,rainfall-type red-bed landslides occur frequently in Sichuan.The slope structure,regional meteorological characteristics and the special physical and mechanical properties of sand and mudstone are the main factors to control rainfalltype red-bed landslides.Such landslides often show the characteristics of sudden,hidden and continuous destruction,and their influence is relatively significant.Based on a detailed field investigation,the mechanical properties of sand and mudstone in the landslide area and the rheological properties under long-term saturated water condition were analyzed through a series of laboratory tests.The deformation and instability mechanism was studied by using UDEC and Geo-Studio software to restore the formation and evolution process of the landslide.The main conclusions are as follows:(1)The plane morphology of the landslide is Tongue,which belongs to the outward slope in a positive direction.The main sliding direction is 150° and the average slope is about 28°.The longitudinal length is about 550 m,the width is about 300 m,the average thickness is about 35 m,the total square volume is about 550×104m3,and it is a large bedding rock landslide.The signs of deformation and failure are mainly troughs,middle and posterior tensile cracks,lateral boundary shear zone,multistage lower fault step and leading edge drum mound.Sliding body movement to the front of the river formed yan Sehu,and the accumulation body is mostly broken,disintegrated.(2)The rock mass rheological test results show that the mudstone rheological deformation is the largest under the primary load,the deformation increase of the lower load is reduced,and the rheological failure is accelerated under the last load.Under the same axial pressure,with the increase of confining pressure,the rock axial deformation is less likely to occur,and the stress and strain increase in the failure.The strength characteristics of sand,mudstone and its structural plane decrease under saturated condition,and the decrease of mudstone strength is more obvious.(3)The mining group landslide is a typical rainfall-type landslide.The deformation and failure mode of the landslide is "slip-pull crack" type.Due to the interaction of heavy rainfall and the rheological properties of soft interbedded mudstone,the failure is finally started.(4)UDEC software is used to simulate and analyze the deformation evolution process of the mining group landslide under different working conditions,and the mining group landslide is basically in a stable state under natural conditions;Under the rheological action,the front edge of the slope is deformed and the back edge has stepped tensile crack.Under the effect of rheology and rainfall,there is an overall slip,indicating that the combination of rainfall and rheology is the key control factor.(5)Geo-Studio software was used to simulate the three stages of the landslide under 3D rainfall in the mining group.The results showed that the surface slope body under 1D rainfall in the mining group landslide was saturated and its stability increased for a short time and then decreased.Under 2d rainfall,cracks cause the saturated zone to expand downward and further reduce its stability.The saturated area of 3d rainfall downhill body is connected and the whole is unstable.(6)Based on the analysis of the disaster causing factors of the mining group landslide,it is speculated that the main influencing factors of the mining group landslide are: terrain with water catchment capacity;The structure of the cut slope,lithologic features with easy softening and rheological features,and high rainfall intensity.Among them,the physical parameter reduction caused by rainfall under the rheological action of rock mass is the main control factor,the dynamic,hydrostatic pressure and seepage force generated by rainfall are the external inducement,and the landslide occurs under the comprehensive factors of the combination of topography and rock mass structure.(7)Under the action of tectonic stress field,the landslide of Mining book formation formed tectonic plane,and the leading river cut downward to form the facing plane;In the early stage of rainfall,the rainfall collected on the slope surface in the front concave topography,the mudstone in the front soaked for a long time softened and mudded,and the slope body produced tensile cracks.The continuous rainfall causes the front edge of the slope to generate hydrostatic pressure with floating support,and the hydrostatic pressure filled with free water of the fracture causes the fracture to open further and expand downward.Rheological action results in intensified macroscopic deformation of the slope body,gradual expansion of fractures at the rear,instability at the front,and overall sliding of the slope body under the traction of the deformation body at the leading edge.