Excavation Mechanical Response And Stability Evaluation Of The Sluice Slope Of Rumei Hydropower Station In The Lancang River

With the development of Tibet's hydropower energy gradually,the construction of large-scale hydropower station has caused more and more problems about the stability of rocky high slope because of the complex geological environment of alpine and gorge.Rumei hydropower station is located in the upper reach of the Lancang River in Markam County,Tibet Autonomous Region Section.The height of rock-fill dam with core wall of the hydropower station is 315 m,which is one of China's and the world's highest dam.The main rock lithology of the sluice slope of the Rumei hydropower station is dacite,and the valley is in the form of deep "V" type.And the sluice slope has the characteristics of steep topography,hard rock,developmental structural plane,strong surface weathered unloading and complex crustal stress field.Therefore,it is of great practical significance to analyze the stability of the excavation of the slope.In this paper,the sluice 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 of the sluice slope under natural and graded excavation conditions,based on the deformation and failure mode to evaluate its excavation response and stability.The main findings are as follows:(1)According to the geological investigation of the sluice slope,combined with the review,the development characteristics of the structural surface of the sluice slope have been identified.The structural planes of the sluice slope are divided into primary,tectonic and supergene structure planes;and according to the grading standard of structural planes,only three structural planes,grade III,grade IV and grade V,are found near the slope.Based on the results of field investigation,it is found that the weathering of the rock at the sluice slope is relatively strong,mainly manifested by the uniform weathering of the surface;The unloading depth is different for ridge and valley,and the former is greater than the latter;There are many landslides in the toe and some gentle slope areas of bank slope.(2)The results of UDEC show that the deformation and failure mode of the sluice slope is consistent with the existing failure phenomena.In the native state,the local position of the surface has a large deformation,but the overall deformation is small.The displacement of the slope is gradually reduced from the slope to the deep,and the displacement of the fractured rock mass is significantly greater than that in the other areas,which is in accordance with the results of the qualitative analysis based on a large number of drift survey data and the field.Under the condition of rainstorm,the total displacement law of the slope has not changed,but the range of the displacement of the slope has increased.When the slope is excavated in different stages,the deformation of the later stage is greater than the previous stage,but the potential unstable block is not formed under the first three stages of excavation until the fourth stage excavation.(3)By means of the finite difference method and the transfer coefficient method,the stability of the sluice slope under natural condition,rainstorm condition and excavation condition are systematically studied.The finite difference method is used to obtain the stress and deformation response under the natural condition and the slope classification condition,and the stability of the potential combination of the slope is quantitatively analyzed by the transfer coefficient method.By numerical simulation,in the natural state,the local tensile stress concentration will appear around the boundary,the fault and the long fissures and the slope is generally considered to be stable.Under the heavy rain,the slope significantly has higher slope surface tension and internal shear stress than the natural conditions.Although the shear strain concentration exists in the slope,the belt has not been through,and the slope in the heavy rain is less likely to be unstable.After the excavation of the first and second stage,the excavation surface at the bottom and its adjacent surface may be damaged.After the third stage of the excavation,the other deformation is not significant except the resilience,and the overall deformation is still large,so the stability of the slope is poor.According to the results of the transfer coefficient method,the stability of the block is poor only under the earthquake,and the slope is stable under other conditions.Only in the condition of earthquake,the block 1 and the block 3 are in a under stable state before the excavation,and the anterior parts of the rock veins of block 1,the block 3 and the block 4 rocks are in the unstable state after that,but the combination of each block is in a stable state.(4)Based on the above research results,the main impact of the sluice slope is the bottom surface of the excavation and the surrounding rock mass which are likely to be unstable after excavation,that is the focus of the slope control.It is necessary to prevent the excavations of the bottom surface and its nearby cutting out around the excavation surface.