| During the running of Three Gorges Reservoir, reservoir water level wouldfluctuated between145m and175m annual. Eservoirs impoundment and water levelcyclical fluctuation will necessarily cause the degradation of bank slope stability indrawdown area and ecological barrier area along the both sides of Yangtze river. Thebank slope has the characteristics of sudden, severe and long-lasting from past bankslope geological disaster which harm to the Yangtze river and its coastal area. Since theimpoundment of the Three Gorges Reservoir,the research of reservoir bank slope hasbecome an important and hot research topic in the field of engineering geologicalresearch. Based on soil bank in the Three Gorges Reservoir Area as the research object,using field investigation and observation,the structure experiment, theoretical analysisand numerical simulation,the following problems are studied:Interaction mechanism ofwater and rock-soil body under water level cyclical fluctuation.The degradationcharacteristics of mechanical parameters for bank slope soil under the condition ofcyclical immersion.The development evolution process of slope body seepage field andslope surface fractures in the process of water level fluctuation. Changing rule of soilbank slope stability and the sudden collapse mechanism of soil bank slope during thereservoir operation. Mainly achieved the following results:（1）Under the action of water level cyclical fluctuation in the Three GorgesReservoir, bank slope failure mechanism can be divided into graded mechanism andmutation mechanism, the former refers to changes of the bank slope stability, while theother one is accidental damage to the bank slope.（2）Based on the experimental study and theoretical analysis, this article hasstudied the interaction mechanism between water and rock-soil body under the waterlevel cyclical fluctuation.what’s more, the writer put the system of interactionmechanism between water and rock-soil body into three three types who aregeotechnical strength effect, water and rock-soil body physical and water and rock-soilbody chemistry in the process of water level cyclical fluctuation in the Three GorgesReservoir.（3）Selecting natural soil at different elevation of typical bank slope and usinggeotechnical test and X-ray diffraction spectrum analysis,the writer analyzedlongitudinally grain size, mineral composition and shear strength parameters of soil at different elevation about the same slope,and got common features of natural soilphysical parameters changes at different elevation and different characteristics ofnatural soil physical parameters with elevation changes.（4）Making an soil parameters test of bank slope,with typical soil bank slope indifferent regions of the Three Gorges Reservoir Area as the research object, the writeranalyzed horizontally the influences of mineral composition,density,watercontent,soil-rock ratio changes and water cyclical immersion on geotechnicalparameter,and analyzed the correlation of the same parameters in the different test typesand the different parameter in the same test type.Finally the writer obtained correlationcoefficient of the same parameters in the different test types and relationship fittingformula and fitting coefficient of the different parameter.（5）Based on soil cyclical immersion test on the typical bank slope in the ThreeGorges Reservoir,the writer analyzed soil physical and mechanical parameters changecharacteristics with different saturation state and different immersion times undercyclical immersion,and revealed the evolution law of soil strength parameters undercyclical immersion.（6）The writer established geological test model to simulate failure mechanism ofbank slope in the Three Gorges Reservoir and formulated experiment operatingconditions to water level changes.The writer obtained change curve of pore waterpressure value at different height of a slope body sliding surface and laws of surfacecracks for slope body spatial evolution in different deformation periods in the process ofthe water level fluctuation by model test.（7）Based on the unsaturated seepage theory, the writer made use of physicalmechanical parameters of slope body material and the test data provided by modeltest,and applied the software Geostudio for seepage analysis to simulate transientseepage field under the condition of water level fluctuation.It Reveals that phreatic linedistribution change law and seepage field change characteristics of slope body in theprocess of water level cyclical fluctuation.（8）Aiming the influence on the stability of different bank slope made under waterlevel cyclical fluctuation, based on typical soil landslide as model, the writer selected6orders of magnitude saturated permeability coefficient on behalf of the different soilmaterials in the Three Gorges Reservoir Area and used saturated-unsaturated numericalmethod to simulate phreatic line distribution change law and seepage field dynamicchange characteristics of different permeability coefficient of landslide body in the process of water level cyclical fluctuation.（9）Considering the transient change of unsaturated matrix suction and seepagefield in the process of water level cyclical fluctuation, stability change trend to bankslope was analyzed under the condition of different permeability withMorgenstern-Price method,which reveal stability changing rule of the soil bank slopeduring reservoir operation.Stability change overall display stability for the bank slope isslow attenuation-stable during the water level rise and acceleration attenuation-stableduring the water level decline.（10）Aiming at the geology structure of soil bank slope in the Three GorgesReservoir, the part below the water level145m is assumed to be strain softening extentsand the part between145m and175m is assumed to be elastic extents. Based oncatastrophe theory and energy principle, the cusp mutation mechanical model of bankslope destroy was builded and bank slope failure criterion is proposed,which wouldeveal sudden failure mechanism of the soil bank slope during reservoir operation. |
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