The Slope Stability Analysis And Bank Rebuilding Forecast About Rentuoxinjie Riverside In The Three Gorge Reservoir Area

As the development of our country's economy at a sustained and rapid speed, as well as the further implementation of western development strategy, the hydropower resources exploitation in our country has entered to the unprecedented stage. Although hydropower engineering brings benefit to generations and plays a positive role in flood-control, irrigation, power and tourism etc, it destroys the geological environment of the reservoir area in the meantime. After the operation of the reservoir, the water level is highly raised. The action of kinds of factors, such as immersion reservoir water, wind wave erosion, runoff erosion, and alternation of drying and wetting, causes the geotechnical condition changing rapidly along the river and the shear strength being greatly decreased, furthermore the stability of the bank slope decreases, and the geological disasters, such as slide and bank collapse, often occurs as well, which are paid attention to by more and more exports and engineers in decades. The analysis methods and theory has continuously forward development, but so far, the stability analysis and reservoir bank collapse prediction mostly adopt relatively independent methods and theory, which usually gives only qualitative classification to the stability of the reservoir bank.According to the practical situation of Rentuoxinjie reservoir bank, sufficiently collected and used the existing data, took the comprehensive means of field survey and investigation, ascertained the basic characteristics of the reservoir bank, found out the engineering geological conditions and statistic the prediction parameter for reservoir bank collapse prediction. Preliminarily considered the deformation and failure model and did engineering geological segmental research. Then, used limit equilibrium method and finite element method (FEM) to carry on quantitative study on the stability calculation and used graphic method to take a prediction for the reservoir bank reconstruction. Based on the preliminary establishment of the stability calculation method and bank reconstruction system, which is suitable for the reservoir bank, the pertinence disposing suggestions for engineering protection measures have been put forward, and the main conclusions are shown as following: 1.Based on the situation that most experts pay more attention on stability qualitative classification at present, the paper puts forward the system analysis method, the combination with stability calculation and bank reconstruction, which suggests that it is necessary to do synthetic analysis and evaluation for stability calculation and bank reconstruction.2.By research on the basic character of the bank reservoir, such as bank reservoir structure, rock and soil type, structural characteristics and its combination type and the distribution characteristics of deformation and failure, the analysis and evaluation of the whole reservoir engineering geology have been done in segment A and B. The bank slope of part A is defined as erosion-denudation type, relatively gentle, stable, suffering wave erosion and with no deformation. The bank slope of part B is defined as whole in erosion-denudation with partly slide type, relatively steep, suffering exterior load due to water level regulation and truck for sand or the like and with significant deformation in front of slope and the possibility of arc slide inside the quaternary soil.3. Build the geological model and mechanical model of each part of the bank reservoir and select six conditions for stability calculate and analysis, which maybe most typically exist, with limit equilibrium theory calculate. The results show that: the stability coefficient of the whole part A bank reservoir is relatively big, which won't occur unstable failure; the stability coefficient of the part B is also relatively big along the interface of filling and quaternary silty clay as well as the interface of quaternary soil and the bedrock, which won't occur unstable failure, but the stability coefficient of slope sliding in arc type inside the quaternary soil is relatively small so that it is on the edge of failure and may occur part-sliding failure.4.Build finite element model to analysis the stress-strain analysis of the bank reservoir, using 2-D FEM, then calculate and analysis the stability of the bank slope in which there would be arc slide inside the quaternary soil. The results show that: the part A is stable; but the stability coefficient of the part B is relatively small so that it is on the edge of failure, which indicates the agreement of the two methods.5. On the basis of stability analysis of the whole and part bank slope, according to actual measured stable slope angle and in the view of project experience in the three gorges reservoir area, the prediction parameter has been obtained for the reservoir bank collapse prediction. Then graphic method has been used to take a prediction for the reservoir bank reconstruction, to obtain the range and ultimate width of the collapse bank for analysis of the development and evolution prospect of its deformation and failure, and get the final topography of reconstruction for the violent degree classification of reservoir bank: the range of bank collapse in part A is slight and it is lower than the elevation of the urban construction, the bank collapse is slight; that in part B is above the elevation of the urban construction and the width is more than 20 meters, so that the bank collapse is strong.6.According to systematical analysis of the results of stability calculation and the conclusion of reservoir bank reconstruction, as well as the natural conditions about the bank slope, the local economic development status and the immigration relocation planning, suggest that: in part A , carry out relocation and preventing collision measures, prevent wave and runoff erosion to the slope surface and strengthen the greening construction in order to protect ecological environment and erosion prevention; the collapse bank of part B is dangerous to 4 households about 12 persons, wharf, two water supply pipes and the road to the wharf etc. Therefore, suggest that, take the engineering protection measures combined with anti-slide pile and retaining wall, with the foundation embedding the intermediary weathered bedrock to make sure the bank slope is stable.The innovations in this paper are the followings: 1. Has put forward the systematical analysis method combined with stability calculation and bank collapse prediction to do comprehensive evaluation by combining of stability calculation and bank reconstruction. 2. Indroducing the stability analysis of FEM into the reservoir bank, which is more likely close to the bank slope actual situation, to calculate the stability coefficient of slope.