Study Of Deformation Mechanism Of Jinlongshan ? Zone Landslide At Ertan Hydropower Station Under The Effect Of Reservoir Water And Rainfall

The stability of reservoir bank slope has a closed relation to the safety operation of the dam, especially which is near the dam. In hydroelectric project, the Vaiont Dam overflowed and flooded in Italy in 1963 are historically profound lessons. A group of international and domestic academics started to turn their attention on the reservoir bank slope subsequently. Jinlongshan landslide near Ertan hydropower station, its deformation and stability is important for this reservoir running. In the engineering background of Jinlongshan ? zone landslide at Ertan hydropower station, on the basis of the twenty years of situ monitoring results, we combined with numerical simulation analysis to study the deformation mechanism of deformation mechanism. First, on the basis of the full knowledge of site and ground and deep of slope empirical data, we described space-time deformation characteristics by four stages(before reservoir impoundment., rapid reservoir filling, trial operation period, normal operation period).we simulated the seepage field of slope under 5 operation conditions: before water storage, rapid reservoir filling, rapid reservoir falling, rainfall, rapid reservoir filling and rainfall) by Geo-Studio software to calculate and analyze. And on this basis we simulated the stress field and deformation field by permeability-stress coupling for 2-D calculation. Finally, combined the theory of seepage mechanics to analyze the reason and mechanism of Jinlongshan ? zone landslide deformation. So far, we got the following results:1. The deformation of slope was subject to rainfall before reservoir impoundment. The ground and deep deformation rate increased obviously in rapid reservoir filling. And it lagged behind of the reservoir water level. The ground and deep deformation rate decreased in September 1998 in trial operation period. Then the displacement increased linearly at a small rate. The ground and deep deformation rate decreased further in normal operation period, there is an association between the ground displacement and rainfall. However, the falling water level has high homologous with deformation of the slide plane in dry season. This shows that drawdown aggravated the deformation of slope.2. The main direction of ground deformation is horizontal direction, and the front of slope upheaved. The ground deformation of landslide was related to elevation and stratum lithologic. The deformation of low-altitude landslide was larger than high-altitude landslide. The deformation of landslide in high strength rock was smaller than that in low strength rock. As the water level is filling, the creeping deformation expanded. The whole ancient landslide deformed along the rock formation of clay by deep deformation.3. When the water level increased quickly, the seepage line showed a new trend of “backflow”. Then the curves flatten. The pore water pressure of ancient landslide increased correspondingly under the effect of rising water level, rainfall and combination of them. Conversely, that dropped with falling water level. When the water level changed, the seepage velocity and hydraulic gradient of ancient landslide near reservoir water level came to maximum. That fits the objective laws.4. The change of stress field focused on the front of slope under rapid reservoir filling, rapid reservoir falling and rainfall. The displacement field changed, and the plastic zone extended. The slope deformed from rising and falling water level. That was caused by seepage force and uplift pressure from the seepage which was formed by that reservoir water and slope interacted. In addition, reservoir water weakened gradually rock strength of slope, the coefficient of stability reduced accordingly. Compared with the rainfall, the effect of reservoir water was more important.5. From the affecting depth, rainfall has more effect on slope ground in a homogeneous medium. Rainfall weakened rock strength of certain depth slope, so the resistant force of slope decreased. However, the sliding force increased with the unit weight of saturated rock and soil, the sliding force of slope increased, the coefficient of stability decreased accordingly. In fact, there were a lot of cracks in ancient landslide. Rainfall flowed to sliding surface along these cracks. The mechanical strength of sliding surface was weakened. Therefore, the deformation became larger.