| Jinping I hydropower station, which is 305m dam height,called highest arch dam in the world for the time being and 3,600 MW installed capacity, is planned to build on the middle-lower reaches of Yalong River between Yanyuan county and Muli county, Sichuan province.Stability problem of high rock slope is rather serious in Jinping I hydropower station. Stability of slopes in the important positions,which directly relates to the security of key project, is extremely significant problem for the engineering construction.The stability of slope at left spandrel groove of Jinping I hydropower station is closely linked with the safety of the buildings in the dam area. The main research object of the paper is the stability of slope described above.By analyzing a large number of survey data, the structure characteristics of the rock mass of slope at left spandrel groove of jinping I hydropower station are studied in detail,and the controlling borderlines of slope deformation are also analyzed. Combined with slope failure phenomena and monitoring information, instability mechanism of slope described above is summarized.On the basis of these, the method of 3D numerical simulation is applied to analyze the deformation of slope, and two-dimensional limit equilibrium method is also used to analyze the left spandrel groove slope. Therefore, the stability of slope described above is acquired finally. The detail content and acquired results are as following:1) According to the geological materials gathered earlier and in excavation period,the structure characteristics of the rock mass of slope at left spandrel groove of jinping I hydropower station,mainly including rock lithological characteristics, rock mass discontinuity characteristics (including faults, joint fissures,unloaded fissures,etc),are carefully studied in the paper. What's more,considering the type of structural plane compartmentalized by their size and property, the controlling borderlines of slope deformation affected by these structures has been illustrated, and rock mass structure model of the left spandrel groove slope has been established.2) According to the evident deformation and failure phenomena during excavation period, combining lithology combination and structure characteristics of slope, mechanism of deformation and failure of slope,and potential failure mechanism has been illustrated. Research indicates that mechanism of deformation and failure of high slope during excavation period mainly contains toppling-slip fracturing , sliding-tensile fracturing and block losing stability.3) Based on the geological prototype slope,The response course under the condition in many steps about spandrel groove slope has been simulated by adopting the Flac3D software.Because of excavation, relaxing zone of slopes developed, rock relaxation deformation is to the direction of free-face,therefore. It is necessary to make a comparison between before and after excavation of stress-deformation of respective slope. Principal characteristic of stress-deformation of"huge block"has been analyzed emphatically.Compared with the deformation of fault f42-9 before excavation, the deformation of fault f42-9 supported by anti-shear tunnels after excavation has converged.It is obvious that anti-shear tunnels worked very well and achieved their intended goal.4) Two-dimensional limit equilibrium method is used to analyze the stability of spandrel groove slope in the excavation with and without supporting conditions, On the results of analysis and calculation, in the excavation without supporting condition, the most dangerous combined slip,that is, the combinations of both lamprophyre vein X and fault f42-9 are commonly unstable.Although stability coefficient of other common is more than 1, safety margin of part of them is not high. In the excavation with supporting conditions,stability coefficient of most potential combined slips inclined to unstable is improved and beyond 1, the whole slope is stable with a certain safety margin.
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