Effects Of Rainfall And Reservoir Water Level On Stability Of Taping H1 Landslide In The Three Gorges Reservoir Area

The overall completion and acceptance of the Three Gorges Reservoir in 2020 has played a good role in flood control,water supply and power generation,which not only brings convenience to the people,but also brings great challenges to the prevention and control of surrounding geological disasters.The deformation and stability of landslides not only affect the development of the surrounding economy,but also affect the safety of people’s lives and property.Taking taping H1 landslide in the Three Gorges Reservoir Area as an example,this paper analyzes the variation trend of seepage field,stability and displacement field of the landslide under different rainfall intensity,different rise and fall speed of reservoir water level and the combined action of rainfall and reservoir water by using the seep/W,slope/W and sigma/W modules in the finite element software GeoStudio.The research reached the following conclusions:1、The cumulative displacement changes of 30 typical landslides in the Three Gorges Reservoir area are counted and found:①The slopes of 30 landslides are mainly concentrated between 10 and 40°.The main constituents of the landslide are silty soil,and the slid zone is mostly silty clay and clay mixed with gravel.The scale of the landslide is mainly large and extra-large.② The sudden change stage of landslide displacement is concentrated from May to July.In this stage,the average monthly rainfall is 150 mm,the decline rate of reservoir water is 0.1～0.3 m/d,and the displacement is 50～300 mm.There are some landslides,such as Woshaxi landslide,whose displacement mutation range reached 5700 mm around July 2008,and some landslides deform at a nearly uniform speed throughout the year,such as Tanjiahe landslide.2、The finite element software Geo-Studio is used to model Taping H1 landslide,and the changes of pore water pressure,seepage and stability are analyzed under different working conditions.(1)Single factor-rainfall conditions.By simulating the stability change of landslide under the condition of only rainfall in a complete hydrological year,it is found that the stability change is small;When the rainfall duration is the same,the stability of landslide changes more when the rainfall is 0.2 m/d than 0.05 m/d.(2)Single factor-rise and fall of reservoir water level.The stability of landslide is synchronous with that of reservoir water,that is,the change trend of stability is almost the same as that of reservoir water;The rise and fall speed of reservoir water level has a certain impact on the stability of landslide.The greater the rise and fall speed of reservoir water level,the faster the stability changes.(3)When rainfall conditions are combined with reservoir water.The infiltration of rain into soil leads to the rise of phreatic line;The change of pore water pressure in the front of landslide shows a downward trend,and the pore water pressure in the middle of landslide shows an upward trend;Under the conditions of rainfall of 0.2 m/d and reservoir water falling rate of 1 m/d,the landslide stability shows a downward trend,and the sliding mass is still in a stable state.3、The deformation of landslide is analyzed by sigma/W module.Under the combined action of rainfall and reservoir water,the reservoir water decreases level at 1 m/d,1.5 m/d and 2 m/d,and the landslide deformation law is as follows:(1)Under different drawdown rates of reservoir water level,the staggered position of landslide is different.The faster drawdown rate of reservoir water level,the shallower the staggered position.The drawdown speed of reservoir water level is 1 m/d,and the staggered position is 55 m below the surface;the drawdown speed of reservoir water level is 1.5 m/d,and the staggered position is 30 m underground;when the drawdown speed of reservoir water level is 2 m/d,the staggered position is 25 m underground.(2)The main deformation area of the landslide is at the front edge and the displacement is 5m.The deformation at the middle and rear of the landslide is small.(3)Located at the monitoring point SB01,the landslide above the sliding surface moves as a whole,and the deep displacement curve is of "D" type;the deep displacement curve at the monitoring point SB02 is of "V" type,with large shallow displacement and small deep displacement;The monitoring point SB03 is located in the middle and rear part of the landslide with relatively small deformation displacement.