Analysis Of Unloading Characters Due To Excavating Abutment High Slope Using Three-dimensional Nonlinear Finite Element Method And Study On Reinforcement Measurements In Xiaowan

Xiaowan hydropower station is located on Lancang River in Yunnan province with installed capacity 4200 MW and height of arch dam 292.0 meters. Stability problem of high slope caused by excavating abutment is worth deeply studying and is listed into tackling key plan of state electric power company. Integrated with the being built abutment high slope in Xiaowan, this paper systematically studies the stability of abutment high slopes. In the analysis, this paper adopts two mechanical models: elastoplastic model and brittle elastoplastic model, and uses the simulated calculative of three-dimension (3-D) nonlinear finite element method (FEM).In hydroelectric projects, the unloading action due to excavation natural rock masses, has great effects on stability of slopes, and the rock's mechanical performance under unloading conditions is very different from loading in essence, especially in the rock masses with joints and cracks. At present, researches for unloading rock mechanics in domestic and abroad have got on slowly, and most of calculation analysis adopt routine results, parameters, models and methods of loading conditions, which are opposite to unloading conditions of excavation works, especially to high slope, leading to discrepant results between calculation analysis and actual measurements. Adopting brittle elastoplastic model, which enough reflects brittle characteristics of rock masses during excavating slope, thispaper simulates unloading action due to excavation and factually reflects mechanical state. At the same time, by using FEM, these parameters such as stress, deformation and basic deflection in rock masses, can be calculated accurately, and the rock masses stability can be calculated quantitatively. Besides, the discontinuous, non-uniformity of rock masses, the nonlinear characters of the stress-strain relation and the anisotropy of its mechanical quantity can be considered too. Not only the elastic deformation of dam body and rock masses can be calculated, but also the developmental and evaluative processes of destroy in the rock masses can be also traced.This paper bears such features hereinafter. First, according to such conditions as topography and geography in Xiaowan, establishing model fully considers the main faults, alternation strips, joints and cracks, and calculative results accord to actual conditions. Second, using three-dimensional nonlinear elastoplastic and brittle elastoplastic model, this paper respectively studies the distribution of stress field, displacement field and failure information during each excavation progression. Third, safety coefficient methods of point strength reserve and integral overload are applied to study on the work performance of rock masses. Through comprehensive analysis, we have found the possible sliding forms of off-stability and the critical area in rock masses. A comprehensive and objective evaluation is made. Finally, through analysis and demonstration, reinforcement measurements are put forward and its working effectiveness is studied.