Study On Strength Characteristics Of Sliding-Zone Soil Of The Bedding Landslide In Jurassic Stratum In The Three Gorges Reservoir

Since the Three Gorges Project was launched,the Three Gorges reservoir has been affected by the rising and falling of water in reservoir area and the infiltration of groundwater and rainfall and so on,which leads to the catastrophic due to the instability of the bank slope of the basin by making numerous old landslide resurrect and resulting in many new-type landslides in reservoir.The Jurassic strata in the Three Gorges reservoir are seen in the interbedded structures of soft-hard(thin-thick)interbedded sandstone and mudstone.What’s more,the thin layer of soft rock is mostly muddy interlayer and the special lithological structure breeds disaster factors in the Three Gorges Reservoir.The study on the characteristics of the strength of the sliding-zone soil has always been the key point of the landslide boundary research and also is the key basis for the stability evaluation and prediction of the landslide.In this paper,the development characteristics of the Jurassic landslides in the Three Gorges reservoir are statistically analyzed firstly.Then,taking Xingfusi landslide in Wanzhou District of Chongqing Province as an example,it gets the disturbing samples by excavating trenches onsite,and takes X-ray powder diffraction analysis,consolidation drainage slow shearing test with different water content and.different SO42-ion concentration,direct shearing and repeated shearing test under different SO42-ion concentration,and then launched triaxial compression test.On this basis,shearing creep tests of sliding-zone soil specimens with different normal stress and water content are carried out.Based on the analysis and treatment of creep curve and stress-strain isochronal curve determined by the test,the creep constitutive equation of Xingfusi new-type landslide sliding-zone soil in Wanzhou was established by using the origin 9.0 self-defined classical Burger creep constitutive model to fit the numerical value.The main results of this paper are as follows:(1)Statistical analysis of developmental characteristics of typical bedding rock landslides in the Three Gorges Reservoir.Taking 30 Jurassic landslides in the Three Gorges reservoir as statistical samples,it finds the landslide types in this area mainly develop in the Upper Shaximiao Formation(J2S)into a large thick landslide,and the elevation of the fronting edge of the Jurassic landslide in the Three Gorges reservoir is mostly between 100 and 175 m.The bedding landslides of this fronting edge elevation is affected by the erosion,scouring and infiltration of the reservoir water under the action of repeated rise and fall of the reservoir water,which makes the landslides most developed.Finally,30 typical stratified bedding rock landslides of the Jurassic in the Three Gorges reservoir were drawn into a polar stereographic projection of slope,bedrock and joint occurrence for further research and analysis.(2)Study on the change of water environment to the strength of sliding-zone soil in bedding landslide.The composition of the sliding-zone soil is mainly clay mineral,quartz,albite,etc.and the clay mineral is mainly composed of illite mixed layer and illite;the water content has obvious influence on the shearing strength index of the sliding-zone soil.That is.the cohesion force will increase with the water content,and the internal friction angle will decrease with the water content.The SO42-ion concentration also has a significant effect on the shearing strength index of the sliding-zone soil.With the increase of SO42-ion concentration,the cohesion force and inner friction angle will decrease.After repeated shearing of sliding-zone soil,the residual strength,cohesion force and internal friction angle will decrease with the increase of SO42-ion concentration.(3)Study on creep characteristics in sliding-zone soil of bedding landslide.The sliding-zone soil of Xingfasi landslide undergoes instantaneous creep and attenuation creep stages before initial failure,and finally stabilizes at constant creep stage at low rate.The larger the normal stress is,the smaller the shearing creep rate and deformation of the slip zone soil will be.The shearing strains are all less than 5%during creep failure under all levels of normal stress.The effect of water content on the shearing creep rate of the slip zone soil is not obvious.The shearing creep modulus of sliding-zone soil is the largest when the water content is lower than the plastic limit.With the proceeding of shearing creep,the shearing creep modulus of low water content and saturated sample will decrease sharply in short time and stabilize at a certain stable value,while the sample with water content slightly higher than plastic limit shows a slowly decreasing trend,whereas the sample with water content close to liquid limit shows a slowly increasing trend;The long-term cohesion of sliding-zone soil is 0.7 times of peak value and 15 times of residual cohesion.The long-term internal friction angle is 0.69 and 0.7 times of the peak value and residual internal friction angle,respectively,and the strength index is affected by the content of fine particles in sliding zone soil.(4)Study on creep model in sliding-zone soil of bedding landslide.The main influence factors of shearing creep of sliding-zone soil are temperature,water content,time scale and other factors;Burgers classical rheological theory model composed of Origin 9.0 self-defined Kelvin body and Maxwell body in series is used to get the relevant model parameters,and the constitutive equation of direct shear creep of sliding-zone soil of Xingfusi landslide is established,which lays foundation and provides significant reference for the internal sliding mechanism,pre-deformation and long-term stability of the landslide in this area.Figure[41]Table[10]Reference[9]...