Deformation And Failure Characteristics And Stability Evaluation Of The Right Bank Abutment Slope Of Rumei Hydropower Station

In recent years,with the development of social economy and the increasing attention to environmental protection,the hydropower resources in Southwest China have been greatly developed and utilized.The stability problem of high-steep slope is one of the main engineering geological problems in the hydropower development,which plays the role of controlling to feasibility,economy and safety of the whole project and is related to the key factors of normal development and operation of hydropower station.RuMei hydropower is the fifth stage of the 7 steps of ChangDu's following river basin planning of Tibet section of LangCangjiang river,of which project scale is first class-big,maximum dam height of which is 315 m,installed capacity of which is2100 MW.The rock mass which develop many small fault and compression joint of the right bank abutment slope whose stability directly affects the safety of dam of RuMei hydropower is heavily weathered and unloaded,and the rock mass structure of slope is complex.With the backing of tutor's research project on“Study on Engineering characteristics and application of dam foundation rock mass“,which is the fourth sub topics on“Study on engineering characteristics and application of rock mass in complex geological environment of RuMei hydropower station on LangCangjiang river,I participated in the investigation of dam site and studied the stability of the right bank abutment slope in detail.The main conclusions are as follows:?1?The lithology is single,mainly for the Middle Triassic ZhuKa formation(T_2z)Dacite.Within a certain range of slope surface,rock mass is heavily weathered and unloaded and slope of dam abutment multiple distributes huge scale fragmentation loosening rock mass,causing structure of rock mass is complicated.Lamprophyre dikes,multiple unloading cracks,long cracks and moderately inclined cracks are developed on the right abutment slope,which affect the stability of the right abutment slope.?2?The structure of the rock mass of the right bank abutment slope are mainly mosaic structure,layered structure and sub blocky structure,while the local structure is fragmented.All kinds of rock mass structures appear alternately in space,which results in complicated rock mass structure.According to the structural characteristics of slope and phenomenon of deformation and failure of slope,deformation and instability mode of the right bank abutment slope mainly include 3 types,namely,sliding failure,toppling failure and local collapse.Sliding failure can be divided into four types:circular sliding,sliding-pulling,wedge failure and plane sliding.According to the structural characteristics of the slope,the main problems existing after excavation of the right bank slope are summarized as the stability of the sliding body composed of gentle-dip unloading cracks and STEEP-DIP small faults or long cracks.?3?The uniaxial compression,three-axis and three-axis unloading experiments of granite and Angan rock were carried out,which obtained the deformation parameters and strength parameters of the rock under different experimental schemes.In order to simulate the response of rock in the process of excavation and back-filling,the variation of deformation parameters of rock in the elastic stage,unloading stage and reloading stage is analyzed and compared by unloading experiments.According to the comprehensive classification results of rock mass,combined with the results of the in-situ test and the values of the rock mechanics parameters of the dam foundation in the standard,the proposed values of the shear?breaking?strength parameters of the rock mass at all levels of the dam site are given.?4?FLAC^3Dsoftware was used to simulate the evolution of slope in dam site.The mian conclusions are follows:1)By trial and error,when the 10 MPa normal stress and the tangential of 12MPa are applied to the boundary of the model,the simulation results are in good agreement with the measured borehole stress.2)When the valley cut to present surface,the bottom of the valley produced a high stress package,and the stress value is 40 MPa,and the distribution of elevation is between2500 to 2610 m.3)The Netherland vein developed on the right bank played a controlling role in the unloading of the right bank slope.4)The scope of the fractured and loosened rock mass on the right bank of the valley and the division of unloading zones of the main adits in the dam site area are reviewed.The results are combined with the field investigation.?5?Based on the finite element strength reduction method,the stability of the right bank abutment slope under natural and rainstorm conditions is calculated.The main conclusions are follows:1)The calculation results show that the overall instability of the natural slope of right bank is likely to occur along the bottom of the strong unloading.The stability coefficient of right bank slope is 1.47,which meets the stability requirements.The stability coefficient of right bank slope under the condition of heavy rain is 1.36,which meets the stability requirements.2)After excavation,the stability coefficient of the right bank slope is 1.37 and 1.26,respectively,under the natural and rainstorm conditions,which can meet the stability requirements.That is,the overall instability of right bank abutment slope under the condition of rainstorm is not possible.?6?Based on the rigid body limit equilibrium method,the stability of the right abutment slope under natural condition,rainstorm condition and earthquake condition is calculated.It is concluded that the three failure combination modes satisfy the safety factor of slope design under natural condition and earthquake condition,and there is no safety reserve problem.Under rainstorm conditions,the stability coefficients of the first two potential instability combination models meet the safety requirements,and there is no instability problem.However,the stability coefficient of the third combination model is 1.187 under rainstorm conditions,which is slightly lower than the design safety factor of 1.30.There is a problem of insufficient safety reserve.Therefore,we should pay more attention to the stability of the third combined mode under rainstorm.