Study On Deformation And Failuremechanism Of Bank Slope In Wushansection Of Three Gorges Reservoir Area

Since 2003,the Three Gorges Reservoir began to impound water.After several stages of impoundment,it first impounded water to 175 m in 2010 and started normal operation after 2013.The reservoir water level fluctuates between 145 m and 175 m annually.Reservoir water and water level changes periodically,up to 30 m of water level changes,will inevitably lead to slope rock and soil in the water-drying cycle of deterioration of the environment,coupled with the addition of water,flood discharge and frequent occurrence of water level Ascending or descending or even combined with the heavy rainfall caused by the complex conditions of moving water,will surely become a new round of bank rebuilding an important force.In terms of reservoir banks in the Wushan section of the study area,the hydrological and geological environment has undergone significant changes due to the precipitation in the reservoir area.The frequent occurrence of disasters in the bank section of the reservoir has seriously threatened the navigation safety of the reservoir area and the safety of people’s lives and properties in the reservoir area.Therefore,it is of great theoretical and practical significance to study the deformation and failure mechanism of the bank slope.On the basis of referring to the regional geological data,this paper collects the typical case of instability of bank slope in Wushan section and carries out on-site investigation of the entire bank.In this paper,we mainly study the long-term strength weakening mechanism of bank slope due to the cyclical fluctuation of reservoir water level in the environment of wet-dry cycling.Through the indoor wet-dry cycle test of typical rock mass on bank slope,the mechanism of deformation and failure of typical bank slope instability and numerical simulation analysis,the following research results are obtained:(1)Through the comprehensive investigation and analysis of the engineering geological conditions in the study area,the study bank segment is divided into sections according to the type and characteristics of bank structure,and the type of the failure of the bank slope failure is divided into erosion type and collapse Sliding type and overall sliding type three categories.(2)The interaction mechanism of rock and soil with water under the action ofreservoir water level rise and fall is summarized and analyzed,and the chemical,physical and mechanistic roles of water and rock mass are expounded separately.(3)The typical rock limestone exposed from reservoir bank in Wushan section was chosen as the research object.Through the indoor wet-dry cycle test,the law of wet-dry cycling of limestone was revealed.The experimental results show that the wet-dry cycle of water plays a gradual role in the deterioration of limestone,and the rate of initial degradation is large.As the number of cycles increases,the deteriorating effect gradually decreases.The uniaxial compressive strength,elastic modulus,tensile strength and the number of cycles of wet and dry limestone are obtained through experiments.The wetting and drying cycle degradation coefficient is defined,which is used to characterize the different parameters of limestone influence level.(4)Based on the research on the failure process and failure mode of the typical bank slope on which the instability has occurred in the Wushan section,based on previous studies,the cusp catastrophic failure model is introduced into the bank slope,145 m underwater part is the strain softening section,and the 145 m ~ 175 m fluctuation zone rock mass is the elastic section,which puts forward the criterion of failure of bank slope instability and reveals the sudden failure mechanism of soil bank during reservoir operation.(5)In order to quantify the weakening effect of soil and rock mass on the slope rock and soil due to soaking,erosion and erosion of wet and dry soils,the weakening coefficient of rock mass is introduced.Taking the Hongyanzi landslide and Gongjiafang2#landslide as examples,the numerical analysis models were established respectively.The landslide displacements,shear strain increments and plastic zones under different weakening coefficients of soil and rock landslides were studied by using FLAC3 D software.Weakened coefficient of soil and rocky bank slope critical critical instability respectively.