Excavation Response And Stability Evaluation Of Left Abutment Slope Of Rumei Hydropower Station In Lancang River

With the development of Tibet's hydropower engineering,the stability of rocky high slope caused by the construction of large-scale hydropower station under complex geological environment of alpine and gorge is becoming more and more prominent.Rumei hydropower station is located in the upper reach of the Lancang River in Markam County,Tibet Autonomous Region Section.The proposed rockfill dam with core wall maximum tower is up to 315 m,the scale of the project for the first-class,which is one of China's and the world's highest dam.The valley that the left bank abutment slope of the Rumei hydropower station is located is in the form of deep "V" type,and the rock lithology is the dacite and the granite?the left abutment slope excavation area is dominated by the dacite?.The left bank abutment slope has steep topography,hard rock,structural plane development,strong surface weathered unloading and complex geostresses.Therefore,it is of great significance to study the response and stability of left bank abutment excavation.In this paper,the left bank abutment slope of Rumei Hydropower Station is taken as the object of study.Through the study of slope engineering geological conditions and rock structural characteristics,the basic academic thoughts combined with qualitative analysis and quantitative analysis are used to judge the deformation and failure mode under excavation of left abutment slope,based on the deformation and failure mode to evaluate its excavation response and stability.The main findings are as follows:?1?According to the early geological survey data of the dam site,combined with the site investigation and review,the rock mass structural characteristics of the slope are identified.The structural facies of the left bank abutment slope are divided into primary,tectonic and supergene structure planes,and the structural planes are divided into grade ?,grade ? and grade ? structural planes according to the structural grading standards.Based on a large number of drift survey data,the author summarizes the weathering and unloading characteristics of the left bank abutment slope.?2?Combining qualitative analysis and quantitative analysis,the potential deformation and failure modes and boundary of slope are analyzed.The slope deformation and failure mode is a stepped sliding-tension or creepage sliding-tension type formed by the combination of steeply dipping faults?or large steep tectonic planes?and mediumly-gently dipping structural planes.There are three potential unstable regions after the excavation of the left abutment slope: one is the fault fp^13-1 and the subterranean joint The potential unstable region;the second is the potential unstable region composed of the fault fp^9-3,fp^9-4 and the fractured rock boundary;the third is the fault zone formed by the combination of the fault zone,the dyke and the long fissure area.?3?Based on the finite difference method and the transfer coefficient method,the stability of the left abutment slope excavation under unloading condition is systematically studied.The finite difference method is used to obtain the stress and deformation response under the condition of slope classification,and the stability of the potential combination of the slope is quantitatively analyzed by the transfer coefficient method.Excavation affects the superficial stress of the slope,where the maximum principal stress decreases ? increases ? decreases.Excavation caused a maximum displacement of about 146.3cm,the maximum deformation outward the slope of about 73.6cm,the maximum downward deformation of about 146.1cm and the maximum rebound value of about 3.2cm.The stability coefficients of the six blocks were obtained by the transfer coefficient method.The results show that the stability coefficient of the blocks?block 2 4?controlled by the small fault fp^9-5 and the gently dipping outside of slope joints is smaller under the natural condition,and the stability coefficient of the block 5 is the smallest.But all the stability coefficients are more than 1.2.?4?Based on the above research results,due to the cutting of the fault,the rock mass instability above the excavation surface may be larger,and it is the focus of the slope control.The block controlled by the fault above the opening line is cut out on the excavation surface.At the same time,the slope of the temporary slope of the bottom will form a rock veins as the trailing edge,growth cracks for the bottom of the block,should be taken seriously.