The Study Of In Situ Stress And Rock Slope Stability Analysis In Deep-Incised Valley

With the gradual implementation of "Hydro-Powder Construction Development of Transmitting Electricity from West to East", a lot of hydraulic project were built or going to be built at deep-incised valleys. Because of the complicated geological condition, geological tectonism, denudation and cutting of the valley, the in situ stress field distribution at deep-incised valley is specially. In addition, the slopes of hydraulic project have a lot of geological discontinuity development, and suffered intensive tectonic activity. The cutting and unloading process of valley caused significant time-dependent deformation, made in situ stress field redistributed and adjusted. Consequently, the excavation slope stability would be influenced by the deformation and stress unloading of rock mass in cut-induced influence zone. To the slope located at deep-incised valley, the geological characteristics need to be considered in stability analysis.The thorough study of in situ stress and excavation slope stability were carried out at Jin-ping hydro-power station, based on the special geologic and geomorphic features of deep-incised valleys. With exhaustive geological survey and data analysis, the valley development and evolution was thought to be one of the most important factors forming in situ stress field. Taking the main factors into consideration, the in situ stress field of deep-incised valley was determined based on field stress testing, by means of stress regression method. In order to apply the regressed in situ stress field into practice, the slope analysis model with rock mass stress should be established, the stress of which can be calculated by space inverse distance weighted interpolation. In the study of 2D and 3D stability analysis of excavation slope, the unloading and relaxation influence of in situ stress upon slope stability was focused. Some results and conclusions in this dissertation have been shown as follows.(1) To the deep-incised valley, the systematic method considering in situ stress was presented. First of all, based on the field stress testing information, the in situ stress of valley could be determined by stress regression method. Then the slope analysis model with rock mass stress was established. The slope stability analysis considering in situ stress was conducted. The presented systematic method is suitable for the deep-incised valleys. The process of which was mainly about: the information of field stress testing—the regression of in situ stress—the stress interpolation—the establishment of slope analysis model—the stability analysis of excavation slope.(2) According to geological survey and data reduction, the conclusion was shown that the development and evolution of valley is one of the most important factors forming the in situ stress field. On the basis of field stress testing of Jin-ping dam area, the distribution laws of in situ stress field were summarized: the zonation of different forming factors; the relaxation characteristic of shallow surface of valley.(3) At deep-incised valley, the main factors forming in situ stress were: self-weight, geological tectonism, and development and evolution of valley. The numerical simulation model with geological features was built, The in situ stress field was determined by stress regression method using FLAC^3D. The analysis result demonstrated the in situ stress distribution of valley, provided basis for in situ stress determination and engineering structure stability analysis.(4) For particular engineering slope at deep-incised valley, the rock mass stress of engineering impact area could be interpolated from the valley model with regressed stress field. The slope analysis model was established with considerations of geological features, structural surface development and rock mass stress.(5) On the basis of slope analysis model, the "in situ stress relaxation force" was; put forward. The force is mean to represent the affect of in situ stress relaxation and unloading on excavation slope, which could be ascertained by finite element information. To take the in situ stress relaxation force into consideration, the improved Sarma method was proposed.(6) According to geological features and engineering conditions of Jin-ping hydro-power station, the stability analysis of engineering slope by improved Sarma method was done. The dissertation first discussed the influence of valley development and evolution on in situ stress formation in detail. The result indicated that the in situ stress plays an unfavorable role in slope stability. It's too risk to analyze slope stability with consideration of self-weight only.