Micro-fracture Mechanism And Stability Analysis Of High Steep Rock Slope During Reservoir Impounding

With the implement of the hydropower development strategy,a large number of large hydropower projects have been established in the southwest region of our country.These hydropower projects have complex geological conditions,and the water level in the reservoir has changed greatly,which makes the problem of the stability of the high steep rock slopes that accompanying these hydropower projects is essential.Therefore,it is crucial to study the deformation disciplines,failure disciplines and the stability of high steep rock slope during impounding period.The thesis focuses on the problem of the stability of high steep rock slopes during impounding period.The right bank slope of Dagangshan hydropower station is taken as the engineering background.Both microseismic monitoring and numerical calculation are carried out.According to the monitoring and calculation results,the progressive failure process of high steep rock slope is showed,the damage mechanism of the slope is discussed,the microseismic activity characteristics are revealed and the stability of the high steep rock slope is evaluated.Furthermore,an early warning indicator of slope instability is proposed by combing microseismic monitoring information and earthquake prediction theory.The early warning indicator provides a new way for warning the high steep rock slope instability for the similar hydropower projects during the process of reservoir impounding.The major achievements of the thesis are as follows:(1)Under the guidance of the thinking that improving the material parameters may be equivalent to the reinforcement effects of anchor cables,the equivalent material properties of the anchor cables reinforcement areas are obtained by numerical calculations.The calculation results show that,increasing cohesion,internal friction angle and elastic modulus have effects on taking the place of anchor cables reinforcement effects.Elastic modulus is more obvious than cohesion and internal friction angle in the aspect of equivalent anchor cables reinforcement effect.(2)For the first time,microseismic monitoring technology is employed to monitor the stability of high steep rock slope in the period of water storage.The major damage areas of the right bank slope are determined by the spatial and temporal distribution of microseismic activities,seismic formation and energy density evolution discipline in the process of water storage.At the same time,the damage mechanism is revealed by numerical simulation in the process of water level increasing.The results indicate that,the anti-shear galleries which at the elevation 1240 m,1210 m,1180 m and 1150 m have effects on resisting the shear deformation of slope weak structure plane when the water level increases.That is the reason why the obvious microseismic activities appeared in these areas in the process of water level increasing.(3)According to the monitored microseismic activities,the major damage area of the right bank slope is defined when the reservoir water fluctuates.In addition,the damage mechanism of the slope is revealed by numerically modeling the local seepage in the slope in the process of water level fluctuation.It is shown that,seepage failure occurred among the diabase dikes ?62,?68 and ?83 and the faults that connected these dikes in the process of water level fluctuation,which caused the micro-fractures in these regions in the process of water level fluctuation.(4)Based on the energy dissipation principle and the viewpoint of progressive slope failure,the safety factor of the right bank slope in the process of water level increasing is calculated by numerical method.The safety factor of the slope decreases with the water level increases,and the safety factor reduced noticeably when the large energy microseismic event occurred in the.slope.The slope safety factor is 1.76 at the end of the process of water storage,which meets the requirements of the code.Therefore,the right bank slope of Dagangshan hydropower station is stable in the process of impoundment.(5)According to the principle of effective stress and the results of microseismic monitoring,the safety factor of the right bank slope is calculated by numerical calculation method in the process of water level fluctuation.It is showed that the slope safety factor reduces due to local seepage in the slope.When the principle of effective stress is considered,the safety factor of the slope is 1.94,which meets the requirements of code.The right bank slope of Dagangshan hydropower station is stable in the process of water level fluctuation.(6)The load/unload response ratio is calculated in the process of water level increasing and water level fluctuation by combining the microseismic monitoring information and load/unload response ratio theory.Furthermore,the load/unload response ratio is proposed as the warning indicator of high steep rock slope failure in the process of reservoir impounding.The warning method indicates that,when the load/unload response ratio is larger than 1.0,the damage appeared in the slope.When the load/unload response ratio continues to increase,more severe damage occurs in the slope,and the slope is risked to instability and the early warning should be carried out.