| After the impoundment of the Three Gorges water conservancy project, the bank slope stability is an important problem facing the reservoir running late. During operation, the Yangtze River water level amplitude up to 30 m about a once-in-a-century before building, while the water level changes each year a few after the completion of the reservoir. Frequent changes in water level will have serious impact on the stability of bank slope. In order to reduce the influence of water level change on bank slope, the main measures is to control the rate of water level at present. Since water to 175 m in 2008, having maintained strict control drawdown rate(0.6 m / day) of non-flood water level, but to some extent, which has limited ability to regulate flood control reservoirs and storage water power generation efficiency, to increase the Three Gorges reservoir flood control, power generation, shipping and other comprehensive benefits and the ability to regulate the water level in exceptional circumstances, It is necessary to increase the declining rate of non-flood water level,let the Three Gorges Reservoir maximize the comprehensive benefit,however,increasing the rate of decline in non-flood water level will cause certain impact on slope stability in reservoir, It is necessary to comprehensive prediction of bank slope stability evaluation under the conditions of increasing non-flood water level drawdown rate.“Huo Shitan” landslide in three gorges reservoir area as an example in this paper, on the basis of the identification of areas and landslide zones basic geological conditions, combined with numerical simulation analysis of the formation mechanism of the landslide, use the landslide macroscopic deformation features and monitoring data analysis landslide deformation mechanism under the condition of rainfall and water level changes, and detailed study its characteristics of seepage field. On this basis analysis and prediction the stability of the landslide under the condition of increasing non-flood water drawdown rate, and the long-term maintain 175 m high water level under the condition of bank slope landslide front has carried on theforecast analysis. Main achieved the following knowledge and research results:(1)Based on the detailed investigation of landslide structure characteristics and the basic geological environment conditions in the landslide area, analyzed the cause of the mechanism of landslide, analyzes the early landslide "slip-cracking" process of deformation and destruction in detail, and adopt the UDEC numerical simulation software recreates the formation process of early landslide.(2) According to the basic characteristics of the landslide, the influence factors and the inducing factors of landslide deformation is analyzed, using the landslide deformation monitoring data in combination with characteristics of macroscopic deformation of slope body, are analyzed the process of rainfall and water level changes of landslide deformation law of activities in detail. The landslide deformation mechanism is studied under the action of rainfall + water level changes, using FLAC3 D numerical simulation calculated the landslide under the natural state, the water level of 175 m and 145 m condition of deformation characteristics.(3)The numerical simulation analysis about the landslide in the process of operation of the reservoir seepage use the SEEP/W module of GEO-Studio commercial software, a detailed analysis of the water level decline and the influence of rainfall on landslide seepage field, and Landslide characteristics of seepage field is studied on the condition of the different rainfall intensity and rainfall duration.(4)Using the SEEP/W and SLOPE/W module of GEO-Studio software, the consideration of groundwater seepage, the reservoir water level keep in the 175 m and145 m stable water level and coupling analysis is made on the stability of rainfall conditions. Head changes caused by seepage analysis of dynamic water pressure and slope caused by hydrostatic pressure of water level, the declining rate of different reservoir water level in non-flood season(0.6m/d,0.8m/d,1.0m/d,1.2m/d), and the non-flood season in 50 years in a simulated analysis of the stability of the heavy rain conditions, it is concluded that a series of dynamic change rule of the slope stability coefficient changing with water level, combining with the analysis of monitoring data,it can be seen that the collapse of rainfall and water level is to induce the deformation of landslide is the most important factors.( 5) Landslide stability calculation results show that the “Huo Shishan”landslide under the condition of stable water level, maintain 175 m high water level is less conducive to the overall stability of the landslide than 145 m low water, mainly due to the high water level increased saturated zone of the landslide mass and a widerrange of rock and soil strength parameters are reduced. Drawdown process and short-term heavy rainfall led directly to the landslide stability continued to decline,the greater the rate of decline in the water level, the lower the landslide stability coefficient, the stability of landslide changes will show some hysteresis in the process of rainfall and water level drops.( 6) According to front composition characteristics of the landslide and the frontal geological structure, determine the bank collapse mode to blunt(grinding)erosion type, and use the Kachujin method to predict the bank collapse under the condition of high water level(175 m). |
