Study On Deformation Evolution Mechanism And Stability Of Cheyiping Landslide Under Water Level Changes Suddenly

At present,landslides have become the second natural disaster in the world,and their severity is second only to earthquakes.In early June 2019,the water level of the Huangdeng Hydropower Station in Yunnan Province plummeted by as much as 33 meters,and dozens of landslides occurred.This paper takes the Cheyiping landslide in the Huangdeng Hydropower Station reservoir area as the research object.On the basis of on-site investigation and sampling,the basic mechanical properties of the landslide soil are analyzed in combination with the indoor geotechnical test,and the centrifugal model test is carried out using the developed reservoir water level lifting system.The deformation evolution mechanism of the Cheyiping landslide under the condition of graded sudden drop of reservoir water level was explored,and the seepage field and stability of the landslide under the condition of sudden drop of reservoir water level at different rates were simulated by Geo-studio software.The main conclusions of the full text are as follows:(1)The centrifugal model test of the Cheyiping landslide was carried out1)Developed a set of water level lifting system for centrifuge,including three-stage water tank,magnetic suction stone,steel wire rope,power line,water inlet valve,water outlet valve,hole pressure sensor,tip plug and water level marking line.Using this system,the water level can be raised and vented,which reduces the complexity of the previous lifting system.2)The macroscopic deformation of the landslide has experienced a process from small deformation to large deformation and then to weakened deformation.The hysteresis degree of the landslide response is water level rise > first sudden drop of water level > second sudden drop of water level.During the sudden change of reservoir water level,the earth pressure is sensitive The soil pressure of the shallow layer in the middle and rear of the landslide is more affected by the deformation of the landslide than the deep layer.The parts with high water content are mainly concentrated in the sudden change of water level,and the farther from the reservoir bank,the lower the water content.3)Evolution mechanism of landslide deformation: in the stage of water level uplift,the landslide deformation is not obvious;during the first sudden drop of the water level,the cracks on the front edge of the landslide collapsed under strong dynamic water pressure,and tension cracks appeared in the middle and rear of the traction;During the second dip,the extension strength of the fault zone was significantly weakened,and the leading edge produced overall slip.It can be inferred that the most dangerous reservoir water level dip rate range for the instability of the Cheyiping landslide is 0.7～1.5m/d.(2)Numerical simulation of the stability of the landslide and the sudden drop of the reservoir water level at different rates was carried out.1)The difference between the results of the centrifugal model test and the numerical simulation is mainly that the numerical simulation cannot reflect the influence of the slope deformation on the seepage field during the test;when the first plunge rate of the reservoir water reaches 1.5m/d,the hydraulic gradient inside and outside the landslide is larger.,the pore pressure isoline moves down more rapidly,the stability coefficient decreases sharply,and the groundwater hysteresis is more obvious.2)Through the landslide stability analysis,it can be seen that the first dip rate range that causes the instability of the Cheyiping landslide is 1.1～1.5m/d,and the secondary dip rate is lower than 1.5m/d.Therefore,in the water regulation of the reservoir area,the focus should be on controlling the sudden drop rate of the reservoir water level.