Study On The Stability Of The Landslide With The Combined Effect Of Rainfall And Rise And Fall Of Reservoir Water Level

Chongqing City is located in the eastern part of the Sichuan Basin,its geological disasters of landslides are extremely developed and it has area frequently and severely affected by geological disasters in China.Based on the survey data of landslide geological hazards from 2007 to 2013 in Wushan County,Chongqing City,the Three Gorges Reservoir Area,the stability of 22 landslides in the study area is calculated under reservoir storage,decline of reservoir water level and rainfall through the use of the transfer coefficient method,and the stability of the landslide groups is explored through the statistics and analysis of the stability coefficient of the landslide under various working conditions.Taking Caojiatuo landslide as an example,considering from the macroscopic deformation analysis of landslide,combining with the professional monitoring data of landslide surface displacement and deep displacement and the reservoir water level scheduling and actual rainfall monitoring data,the influence of rise and fall of the water level and rainfall on the stability of the landslide is analyzed systematically.The fluid-solid coupling study of the landslide is carried out by FLAC3 D and the effects of different storage height and different decline rates of reservoir water level on the stability of the landslide are discussed.The paper has mainly achieved the following research results and conclusions:(1)When the reservoir is stored from 135 m to 160 m,as the water level rises,the overall stability of the landslide group gradually decreases.When the reservoir water level is stored from 160 m to 175 m,the stability of the landslide group increases with the water level rise.When reservoir storage and rainfall,total stability of landslide group has declined;When the water level drops from 175 m to 145 m with the rate of0.5m/d,1m/d,1.5m/d and 2m/d respectively,the overall stability of the landslide groups decreases step by step with the increase of the decline speed;When the rate of0.5m/d decreases from 175 m to 145 m,the rainfall intensity is 0.02m/d,0.05m/d,0.1m/d and 0.15m/d respectively,the stability of the landslide group decreases gradually with the increase of rainfall intensity;When the rainfall intensity is 0.15m/d,the landslide group is in an unstable state as a whole;when the reservoir water level decreases at rate of 1m/d,the landslide group is in an unstable state under different rainfall intensities and the stability of the landslide group decreases gradually with the increase of rainfall intensity.Quantitatively,the stability coefficients of each landslide are different under different working conditions,the farther the landslide is from the Yangtze River,the larger the stability coefficient is.(2)From 2007 to 2013,the displacement change of the Caojiatuo landslide increased step by step,and the reservoir area was in the low water level stage,that is,from May to September each year,the overall displacement of the landslide increased greatly,especially in 2009 and 2012,the displacement changes greatly;when the reservoir area is in the high water level stage,from October of each year to April of the following year,the incremental change of the displacement of the landslide is small.The surface deformation of the A zone is severe,and the surface deformation of the B zone is relatively stable.At the same time,the rainfall also has a certain impact on the displacement deformation of the landslide.(3)From the deep cumulative displacement monitoring data,the overall movement has produced above the slip surface,the central and leading edges of the landslide are strongly deformed,the trailing edge deformation is relatively weak,that show the characteristics of the traction landslide,and the stability of the landslide deteriorates year by year.There have been two surges in deep displacement in 2009 and 2012.(4)Through numerical simulation analysis of Caojiatuo landslide,it is found that the stability coefficient of the landslide is 1.043 when the initial storage height of the reservoir is 135 m,which is in a under-stable state;when the reservoir storage height is 160 m,the stability coefficient of the landslide is 1.003,which is in a critical instability state;When the reservoir water storage height is 175 m,the stability coefficient of the landslide is 1.074,which is in a basically stable state.When the reservoir water level is reduced from 175 m to 145m(decline rate is 0.5m/d),the stability coefficient of the landslide is 1.039,which is in a under-stable state;When the reservoir water level is reduced from 175 m to 145m(decline rate is 1m/d),the stability coefficient of the landslide is 0.996,which is in a instability state.(5)Based on the numerical simulation of fluid-solid coupling,the pore water pressure distribution and variation characteristics of Caojiatuo landslide under different water storage heights and different decreasing rates are discussed.