Stability Analysis Of Surrounding Rock Of Yebatan Underground Powerhouse

At present,most of hydraulic engineering projects in China are located in the southwest areas,where there are abundant hydropower resources.Due to the alpine and canyon terrain in these areas,underground powerhouse is very common in the layout of hydraulic structures.Geological conditions are complex as several seismic belts are distributed in the southwestern region.There is a considerably higher probability to encounter poor geological conditions in construction areas.Large scale,structural complexity,difficulties in construction are typical for the underground powerhouse of hydropower station.To ensure the safety of powerhouse in both construction and operation periods,the stability analysis of the surrounding rock is important.The stability of surrounding rock is affected by various factors,such as in-situ stress,geological faults,mechanical properties of rock,groundwater,excavation sequence,supporting methods.In view of these factors,the Yebatan hydropower station on the upper reach of Jinsha River was taken as an example,and applied the finite element numerical method to analyze the stability of the surrounding rock of the underground powerhouse caverns.The optimal design scheme was chosen,based on the findings of the simulation,which also provide valuable reference to the design and construction of underground powerhouse.The content of the study mainly focuses on the following six aspects.(1)I constructed an appropriate numerical simulation model and adopted least square regression method to obtain the initial stress field as an approximation to the real initial stress field,based on the in-situ stress data from geological Prospecting.The initial stress field of the two-dimensional model can also be derived from the initial stress field of the three-dimensional model by coordinate conversion.(2)Due to the complex geological conditions of the factory region,it is difficult to establish three-dimensional models with large programs.So I constructed a two dimensional model to study the stability of the surrounding rock under different layout scheme.Based on the results,the best layout scheme can be selected.The optimal axial direction and cavern interval can also be determined.(3)The structures of underground powerhouse caverns are complex.Normally,excavation is conducted by steps and layers.The stable state of surrounding rock will bedestroyed after excavation,resulting in rock stress redistribution.A different sequence of excavation results in a differently redistributed stress field.So I analyzed the stability of the surrounding rock under different excavation sequence with the three dimensional elastic-plastic model,and determined the optimal excavation sequence.(4)The impacts of supporting method on the stability of surrounding rock were studied.Specifically,I evaluated the effectiveness of several methods,including shot-shotcrete,prestressed anchor and cable.(5)As the underground powerhouse is located near the arch dam abutment,arch thrust is added in the model as a kind of load.I also evaluated the impact of arch thrust to the stability of the surrounding rock.(6)The stability of the surrounding rock was also evaluated with an integrative consideration of supporting method,arch thrust and seepage in the model.