Stability Analysis And Estimation Of The Complex Slope Closed To The Dam In Southwest Of China

A hydropower station in Yunnan province in southwest of China, locats in North West to Foshan LiuTong village on the upstream of Lancang Jiang River.The hydro-power station is the first stage of cascade development of Yunnan Lancang River Hy-dropower planning, which is the leading reservoir, upstream to the GuXue cascade hydropower stations located in the Tibet Qamdo Markam County area, and down-stream to the GuoNian cascade hydropower stations. Close to the upper reaches of left bank of the dam site location, distribution of a large glaciofluvial deposits, and there is strong deformation in underlying bedrock, the failure of the slope will be a great threat to the safety of the proposed dam site and operantion.This paper based on the complex slope closed to a dam in southwest of China as the research object,investgat the back of regional geology, geological environment, as well as the structural features , physical and mechanical properties of glaciofluvial deposits ,the structural characteristics of toppling deformation rock. Research based on the geological origin analysis combined with numerical methods toppling defor-mation formation mechanism is analyzed; and then, analyzing deformation and failure mechanism of the slope in post-storage, and the use of limiting equilibrium methods and numerical calculation methods are analyzed to the stability of the slope. The mainly thesis and the results are as follows.(1) The deposit closed to the dam is composed with fluvial sand and gravel lay-ers on the bedrock layer, glaciofluvial deposits and fluvial sand and gravel layers on glaciofluvial deposits. The glaciofluvial deposit is mainly composed with gravels, in part of which has weakly clay cementation, and there is almost not obvious gap be-tween the gravels, that have a certain orientation, and some layered phenomenon.(2)The formation and development of toppling deformation rock can be divided into the following three processes:①The first phase of the Lancang River valley to the fast incision make regional stress field adjust significantly, resulted as the maximum principal stress along the slope direction that shows a strong compressive stress, and minimum principal stress situating at right angles to the slope direction that shows tensile stress. As the result of rock stress conditions changing, the terrene is squeezed outside direction to the slope and toppling to the direction of the valley with deformation.②In the second stage, the rock on the faultage unloads and rebound with the rock moving towards the direction of outside the slope (due to differences in the character of rock, mainly for the difference in rebound), as a result, the rock mass be-come broken and there is obvious deformation and expansion in the rock mass. Moreover because of the faultage F1 compressing- toppling deformation, the upper rock mass topples downwards furtherly. During the upper rock mass toppling, the roots of rock parallel to the slope generated "V" fissure was the huge moment gener-ated in the process leading to.③In the last stage weathering and unloading leading to the stress field of the faultage F1 readjusted result in further compression-deformation. And thus make the upper rock mass topple down furtherly, resulting in "V" fissure development until the formation of folding cross section. Finally, the part of the scope of the plastic zone form on the folding surface。Using limit equilibrium method and numerical calculation methods accumulation body under different conditions in the stability analysis shows that:①Under the natural state and the conditions of continuous rain, the entire gla-ciofluvial deposits closed to the dam was stable, whether the part o or overall of the stability of glaciofluvial deposits can meet the engineering requirements;②Before the reservoir storage, in front part of the glaciofluvial deposits is going to be failure for the limit equilibrium stability, under the storm +Ⅶseismic conditions, and the stabil-ity of the whole glaciofluvial deposits is better.③I n front part of the glaciofluvial deposits closed to the dam could maintain stability under the post-storage, but the safety coefficient of the glaciofluvial deposits is small, and the stability of the the the whole glaciofluvial deposits is better.The stability of the toppling deformation rock mass can meet requirement under the post storage condition.However, the discon-tinuous surface in the toppling deformation rock mass, of which the structure is not intact, is concentrated. Therefore, it not excluded under the influence of adverse fac- tors in the form of partial collapse of he toppling deformation rock mass.⑤While post-storage, in front part of the glaciofluvial deposits is going to be failure for the limit equilibrium stability, under theⅦseismic conditions,and the stability of the whole glaciofluvial deposits is better.⑥The range of the slope going to be failure limits mainly to the water level changes within the slope, and the slope that will be failure as a whole is less likely to occur.In summary, either the part or the whole of the glaciofluvial deposits closed to the dam is stable, before the reservoir storage, and theⅦseismic load is not consid-ered in the condition;if theⅦseismic load and rainstorm is considered together, in front part of the glaciofluvial deposits is going to be failure in the extreme condition, but the the overall stability could meet the requirement. The whole of the glaciofluvial deposits closed to the dam is stable, under the post storage not considering theⅦseismic load.But the safety coefficient in front part of the glaciofluvial deposits.is not enough.And considered theⅦseismic load, the part of the glaciofluvial deposits closed to the dam is going to be failure, but the whole of the glaciofluvial deposits is stable as well as the toppling deformation rock mass, under the post storage condition.