Research On The Stability Of Landslides Impacted By Increasing The Drop Rate Of Reservoir Water Level In Three Gorges Reservoir Area

The instability of the reservoir bank landslide was a kind of geological disasters along with the hydropower project construction. The landslide instances induced by reservoir built at home and abroad were not rare,and some caused great casualties and economic losses, and even project scrap.Because their conditions were complex and the effected factors were diverse, they spread widely and frequently, generated so multifarious and complex that made the prediction difficult and the governance be expensive.They had always been one of the major engineering geological problems in our country.Since the three gorges reservoir region was built to store water,the water level in front of the dam had always been changing between 145 m to 175 m.The changing of water level was very easy to lead to generate engineering geological hazard and instability of the reservoir bank landslides.Taking the ErCengYan landslide in three gorges reservoir area as an example,considering the geological conditions of the study area and the scheduling conditions of the water level in three gorges reservoir,the stability of landslide was simulated and analyzed under different rate of water level.Summarizing the analysis of the instability mechanism of reservoir bank landslides and the research results of saturated-unsaturated seepage, the five different water level in different declining rates were simulated by combining with the data of water level scheduling in three gorges reservoir, and the software Plaxis was used to simulate the landslide.The conclusions are as follows:(1)The stability relationship between the three gorges reservoir water level decline and slope body.Analyzing the three gorges reservoir area landslide examples by using historical monitoring data,the reservoirs have an impact on the stability of slope in reservoir area,and it will change observably especially in the process of water level decline. Fast down water caused the landslide body dynamic water pressure, this is wade old landslide collapse collapse and the new one of the important dynamic factors of landslide.(2)Analyzing the influence factors of landslide stability. Established a classic model to study out that,if the landslide slope toe increased, the possibility of landslide instability also increased; and if the soil permeability coefficient increased, the landslide stability increased; but if declining rate of the water level improved,the safety coefficient of landslide would decrease.(3)The changing of water level caused the changing of seepage field in landslides. In process of saturated and unsaturated seepage,the saturation line did not decline immediately as the drawdown of reservoir water level inside landslide,there was an obvious lag. The saturation line declined quickly at the place close to the reservoir water level, and it declined slowly at the place far from the reservoir water level.(4)Increasing of the declining rate of water level changed the landslide stability. Changing the declining rate of water level based on the theory of unsaturated soil mechanics to analyze the saturability,matric suction,stability and the change law of the most dangerous sliding surface of landslide.The results showed that, in process of increasing water level declining rate, the saturation of slope increased gradually, the matrix suction decreased, the horizontal displacement landslide largened, and the stability coefficient lessened.(5)Using two kinds of method to calculate the landslide stability and compare. Using two methods to calculate the stability of the landslide, which are the traditional limit equilibrium method and finite element strength subtraction. The results showed that, when the water level drop rate increased, the stability coefficient of landslide gradually reduced, and when the water level decline rate was set to 1.2 m/day, the stability coefficient of slope was the lowest. The two calculation results were different.The calculated stability coefficient of the whole accumulation along the bedrock by using the traditional limit equilibrium method was smaller,while the calculated stability coefficient of the leading edge of shallow by using the finite element strength subtraction was larger.