Research On The Stability Of Yumenzhen Reservoir Landslide In Ertanhydropower Station On Yalong River

With the construction of hydroelectric station, reservoir landslide, as a common geological hazard, has been paid more and more attention in recent years. The Yumenzhen landslide is located in the reservoir area of Ertan Hydroelectric Station,which keeps deforming when the creep slide happened in the long rains of 1996. And the deformation becomes particularly obvious if the water level of the reservoir drops. According to the geological features and deformation history of the Yumenzhen landslide,this thesis tries to analyze its development mechanism and main factors systemically, makes sure the saturation lines through a variety of methods and records the stability of the landslide in different situations. The influence of the fall of water level and the permeability coefficient of the reservoir bank to the landslide’s stability is analyzed by GeoStudionumerical simulation method. In the end, the thesis will draw lessons from the failure causes of this project and propose some advice to the landslide control. The main results are as follows:(1) The landslide is located in the reservoir area of Ertan Hydroelectric Station, with Yumen Town in its west. The upside of the landslide is steep while the lower part of the slope is relatively gentle, which is ladder-shaped on the whole. The overburden layer is composed with man-made filled soil and silty clay which have loose structure and poor mechanical properties and become worse when they absorb water. The subterrane is hypabyssal rock of Xigeda Formation which is easy-sliding and weakened when it absorbs water. Its seismic intensity is Ⅶ degrees. Every year the rainfall in the landslide area is asymmetric, especially from May to October. What’ more, its surface water is rather abundant, for the normal highest level of the store water can be achieved to 1200m and the lowest level is 1155m. The normal storage period lasts from September to February of the following year. When the reservoir area is in normal operation, this landslide will be wholly submerged in the water.(2) Under the influence of the reservoir’water level and rainstorm, the Yumenzhen landslide keeps deforming when the creep slide happened in the long rains of 1996. The landslide deformation shows apparent relevance with the change of the reservoir’ water level. It is shown that when the reservoir’water level decreases, the land slides. More quickly the water level decreases, more apparently the land slides. When the reservoir’water level increases or the water level is high, the landslide keeps deforms less obviously. The landslide is influenced by many factors, among which the change of the water level is the most important factor.(3) This thesis tries to make sure the saturation lines when the reservoir’water level decreases through a variety of methods. And by calculating its stability, this thesis will make evaluations for the landslide’s stability in different situations such as high water level and rapid drawdown of water level. With the help of GeoStudionumerical simulation, it is achieved that the stability of the Yumenzhen landslide significantly decreases first when the water level falls down, then it fluctuates after reaching the minimum. Generally the stability coefficient decreases first then increases. There is an unfavorable water level, which is 1178m to the main landslide body and 1190m to the subordinate landslide body. The more quickly the water level decreases and the smaller the permeability coefficient is, the worse it is to the stability of the landslide.(4) By analyzing the failure causes of the existing anti-slide piles and summarizing the shortcomings of piles positions and the depth of anchored segment,this thesis proposesa treatment scheme of pulling up the piles and deepening anchored segment.