Tibet Songta Hydropower Station Dam Plunge Pool Slope Instability Mode Research

SongTa hydropower station lacates in ChaWalong of ChaYu country in Tibet.It is the biggest station in NuJiang river.Its dam elevation is 1928 m and the proposed dam height is 318 m.The proposed dam style is designed in concrete hyperbolic arch.The normal water storage elevation is 1925m and the back water height in front of dam is about 235m.The great water head will lead strong atomizing conditions during releasing flood in station's normal running period,which results in hydrogeology condition's obvious changes of the water cushiuon pond's slope.So,the water cushion pond has the possibility of instability.If it loses stability,SongTa station's normal running and the downstream will be in great danger.Obove all,there is a need to analyze and demonstrate instability mode and stability of the water cushion pond's slope.Based on the understanding of engineering geological conditions of the study area and the actual the phenomenon of deformation and destruction.with the help of FLAC^3D numerical analysis software to simulate the calculation of slope plastic zone and stress field changes;with the aid of MODFLOW software to simulate and analysize changes of underground seepage field in different conditions;with the limit equilibrium method software Slide to solve water cushion natural slope stability in several conditions.With the help of above numerical tools,the slope failure mode of the water cushion pool is analyzed.There are following results and understandings:?1?Study area's deformation failure phenomenon includes steep fissure intensive zones and steep opened fissure;mid-gentle angle shear fissure concentrated zones.The combination of steep dip structure surface and gently dipping structural plane acts as the slide and crack deformation and failure mode.?2?With the help of the software of FLAC³DD numerical analysis of instability mode,selecting typical deformation signs found to add to the basic model,which act as weak structural surface characters.The conclusion is that the most obvious stress waving place lies in the weak structural plane,and it reveals that the plastic zone changes also validate the previous results of ladder shapped instability mode.?3?The key of water cushion pool slope stability analysis is about reservoir flood discharge atomization effect.In order to get seepage field of the water cushion pool slope in the atomization conditions,using three dimensional seepage numerical simulation software Visual MODFLOW.The analysis results showed that,under the different water level conditions,as the reservoir water level gets higher,the rise of ground water level gets higher;and in the atomization,storm,natural these three conditions,underground water level elevation of the atomization condition is the biggest,followed by heavy rain conditions.The change of seepage field affects the stability of the whole slope.?4?In the slope stability of Slide method,water cushion pond slope S5?S6profile are selected.The calculated results show that the water cushion pool slope in several conditions,their stability are in basic stable or stable state.Compared with the aforementioned strength reduction method,Slide analysis model must aim to solve the slip plane of different combinations of the structure surface,and different combination modes will draw different steady states.?5?The focus of this thesis is the water cushion pool slope instability mode.Based on the combination with several numerical simulation results and the analysis of existing signs of deformations and damages,forecasting water cushion pool slope instability mode in atomization condition still is slide and crack type instability mode in the ladder shaped combination form.