Deformation Characteristics And Evolution Mechanism Of Jiuxianping Landslide Induced By Reservoir Water And Rainfall In Three Gorges Reservoir Area

This paper relies on the key project of the Technical Research Center for Disaster Prevention and Control of the Bank Slope and Engineering Structure of the Three Gorges Reservoir,"Study on the Revival Mechanism and Stability of the Bedding Rocky Ancient Landslide in the Three Gorges Reservoir Area".On the basis of the research results of the regional geological environment,this paper clarifies the development characteristics of the Jiuxianping landslide;Based on the monitoring results of the water level,rainfall,and surface of the landslide reservoir during the period from July 2016 to July 2017,combined with indoor experiments to obtain the physical and mechanical properties of the sliding zone soil of the Jiuxianping landslide,the working conditions under different intensity factors are set,and finite element software is used to simulate the impact of the reservoir water level and strong rainfall coupling on the stability of the Jiuxianping landslide during the period,elucidating the mechanism of landslide deformation evolution;Adjust the intensity factor conditions applicable to landslides in the Three Gorges Reservoir area and conduct numerical simulations;Calculate and verify the stability of the landslide after numerical simulation based on reliability and failure probability.By fitting and training the displacement prediction model,the landslide displacement and deformation prediction is carried out,and the deformation evolution trend of Jiuxianping landslide is deduced.After research and analysis,the following conclusions have been drawn:1.The front edge of the Jiuxianping landslide was eroded and cut by the Yangtze River,resulting in a decrease in the resistance to sliding force at the front edge.Under the action of self weight,the rock mass underwent unloading sliding along the bedding weak structural plane,leading to further development of rock fractures.The rock mass was cut into block fractured rock masses,and the strength further decreased,laying a material foundation for subsequent sliding.The slope of the landslide is15°-30°,with the upper part of the profile being a nearly linear shape and the lower part being a platform,inclined at 140°,providing deformation space conditions for rock sliding.The formation and development of the tensile fracture zone in the middle and rear of landslides provide a place and transport channel for groundwater activity,accelerating the formation and connection of sliding surfaces,which is unfavorable for the stability of landslides.2.The drawdown of reservoir water level is the main inducement to control the displacement and deformation of bedding landslide.When the water level drops from160m to 145m,the stability coefficient is the lowest and is 1.206.At this point,the direction of seepage force in the landslide body is downward along the slope,and some sliding masses have changed from the original floating weight to natural weight.The increasing sliding force causes the overall deformation and sliding downward,squeezing the front sliding mass.The rear of the landslide will deform downward due to traction,ultimately forming tension cracks,which affect the overall stability of the landslide;During the drawdown period of the reservoir water level and the 145m stable water level period,the strong rainfall further induced the displacement and deformation of the landslide,and the stability coefficient decreased to the lowest of1.159 under the rainfall intensity of 150mm·d^-1.Heavy rainfall promotes and further induces the displacement and deformation of the landslide.The greater the rainfall intensity,the smaller the rate of reservoir water level decline required for the landslide deformation,and the two compensate each other.3.During the rising stage of the reservoir water level,some sliding bodies are affected by the reservoir water and will generate buoyancy force.The direction of seepage force points towards the slope,and the deformation of the landslide body is less obvious;When the reservoir water level stabilizes to the high water level stage,the seepage inside the slope tends to stabilize,with strong buoyancy and hydrostatic pressure as support,and the deformation of the landslide body is still relatively weak.In terms of the failure probability of the Jiuxianping landslide,the failure probability of a sudden drop in reservoir water level ranges from 30%to 47%,and the reliability index is positioned between 0.24 and 0.56;When the water level of the reservoir drops at a rate of 0.5m·d^-1,the reliability index is more than twice that of the 2m·d^-1working condition,and the failure probability is reduced by 43%compared to the previous condition;At the same time,under the condition of superimposed rainfall,the greater the rainfall intensity,the lower the reliability index,and the greater the probability of failure.4.The deformation displacement of the landslide within 680 days from January2023 to November 2024 was predicted,and the maximum displacement was calculated to be 55mm.The most important factor affecting the stability of the landslide mass is the rise and fall of the reservoir water level,which will affect the stability of the landslide mass and eventually lead to large displacement of the landslide mass.But the effect of the reservoir water level on the stability of the landslide is weakening over time,and the prediction eventually tends to be stable as a whole.To sum up,under the effect of reservoir water level and rainfall,it is predicted that Jiuxianping landslide will be stable in the future.