Study On Bank Collapse's Type And Mechanism In Mountain Reservoir

The damsite of Xiaowan hydropower station is on the border between Lincang area's Fengqing country and Dali area's Nanjian country, which is in the middle of Lancang River. The reservoir is main-reservoir which is located in the section of middle and lower reaches of cascade hydroelectric power stations. It is the key project of Lancang cascade development. Library normal storage level elevation is about 1240 meters; it's divided into east and west region. The east is Heihui river reservoir, its library length is 123 kilometers, the west is Lancang River reservoir, and its library length is 178 kilometers. The tail area of the Lancang River is located in the upstream 2 kilometres of Xiaozhai village which belongs to Yunlong country Jiuzhou Township. The backwater elevation is 1278.59 meters. The length of reservoir banks is 597 kilometers. The tail of Heihui River is in the Xucun station where backwater elevation is 1245.61 meters, the length of the reservoir bank is 432 kilometers.The natural balance of slope is changed after the impoundment. The interaction between water and rock makes slope instability and failured in special conditions. That is what we called the bank collapse. In this paper, Xianwan reservoir is used to be an example to study the bank collapse type and mechanism of mountain reservoir, in a large field investigation, the slope structure and bank collapse factors was identified. The conceptual model of each type of bank collapse was estabilished to analyze the deformation and collapse mechanism. The development and evolution of each bank collapse type by numerical simulation is used to conclue the bank collapse's type and mechanism, the main contents and conclusions are as follows:(1)Based on the existing data, a large field investigation of Xiaowan reservoir was used to check out the engineering geological conditions of the reservoir bank section. It includes slope material composition, slope morphology, slope stucture, the slope's hydrogeology conditions.(2)Depth analysis of the slope stability affecting by the slope structure on the Bank is used to devide slope into the soil slope, rock slope and rock mixed soil slope, Rock slope is divided into bedding slope, Escarpment slope, cross slope Etc., Then we analyze how the structure of each slope is affecting on reservoir bank's stability, and further investigation is used to check out the slope and the situation of bank slope stability.(3)The distribution of slope collapse was indenfied in Xianwan reservoir; it includes both banks collapse of the river, shape and size of bank collapse, bank collapse occurrence of geological environment. Field survey data which is used to statistical analysis is used to summarize the types of Xiaowan reservoir bank collapse, there are three types of bank collapse, slump type, slip type and slump-slip type. The slump type of was widespread in slope deposits, weathered layer, residual soil slope of the collapse sections of the reservoir area, It is accounting for 85% of the total number of bank collapse.(4)The factors of bank collapse is analyzed in this paper, it includes water level, slope soil characteristics, bank morphology, human activities and other factors and so on. Each bank collapse is controlled by one factor or several. The influence factors are often different by different bank collapse type.(5)Each bank collapse mechanism will be analysised from the bank collapse's evolution and the development as two aspects, then it is combined with specific projects for further examples of the formation of bank collapse, at last we use numerical simulation to verify bank collapse's development and evolution. The main analysis includes contour of displacement, maximal shear strain, minimum principal stress and plastic zone.