| There are many large-scale landslides with large scale and strong harm in the Three Gorges Reservoir area.Bazimen landslide as a typical accumulation landslide,the revival mechanism is complex.There are obvious local deformation phenomena in the slope.It is of great significance to clarify the relationship between the local deformation and the overall deformation,analyze the revival mechanism of landslide and establish the initiation threshold for the disaster prevention of accumulation landslide.This article takes the Bazimen landslide as an example,delineates landslide zones through on-site inspections and actual deformation characteristics,analyzes local deformation mechanisms,and clarifies the relationship between local deformation and overall deformation.Based on the monitoring data over the years,analyze the types of deformation inducing factors,obtain the response law between the deformation of the Bazimen landslide and the reservoir water and rainfall,and establish the threshold values for the reservoir water,rainfall of the Bazimen landslide;Establish a two-dimensional finite element numerical calculation model for the Bazimen landslide to analyze the seepage characteristics,deformation characteristics and stability changes of landslide under the coupling of reservoir water and rainfall,and to reveal the landslide revival mechanism.The main contents and achievements are as follows:(1)Basic characteristics,deformation zoning and local deformation characteristics of Bayzimen landslide.The length of the landslide is 550m,the width is 80～500m,the average thickness is 30m,and the total volume is 400×10~4m~3.The front of the slide is 5～10°slower and 30～50m thicker,while the rear is 20～35°steeper and about 10m-30m thinner.The deformation mode of the landslide front has shifted from step deformation to slow creep,and the deformation area is concentrated in the middle and rear of the landslide.The deformation of each part of the landslide is affected by different factors,and the left side of the landslide is more sensitive to rainfall.According to the degree of deformation,the landslide can be divided into the rear sliding zone,the front anti-sliding zone and the steep and gentle junction zone.There are four local deformation areas within the landslide,and the local deformation in the steep and gentle junction area is obviously larger than the overall deformation of the landslide.The bank collapse is formed under the action of reservoir water erosion and fluctuation.The relationship between the overall deformation and local deformation is clarified.The overall deformation of landslide accelerates the local deformation and the impact of local deformation on overall deformation is relatively small.(2)The deformation response rules of landslide under reservoir water and rainfall conditions.The displacement curve of Bazimen landslide presents a periodic"step"increase under the action of reservoir water and rainfall.The displacement of a"step"is mainly between 40～100mm,and the step time is concentrated in May to July every year.The rapid decline of reservoir water will lead to the step deformation of landslide,and the generation time of landslide deformation lags behind the decline time of reservoir water level.The greater the decline rate of reservoir water,the greater the step displacement of landslide,and the earlier the start time of displacement deformation.In 2022,the reservoir water was scheduled for trial operation at a decrease rate of 1m/d for the first time,and the displacement step of Bazimen landslide in 2022 increased by 40%～63%compared with 2021.When the water in the reservoir drops from 175m to about 150m and the daily decline rate decreases at a rate of0.6m/d,the landslide begins to deform in about 30 days.When the water in the reservoir drops at a rate of 1m/d,the time is shortened to 16 days.In the step deformation induced by rainfall,the displacement rate can reach 27.1mm/d,and the rainfall can cause the severe deformation of landslide.The step deformation of landslide has a certain lag,the lag time of reservoir water induced deformation is nearly 20 days,and the lag time of rainfall induced deformation is 9days.(3)The threshold of the revival of the Bazimen landslide.According to the evolution characteristics of the displacement and deformation curve of landslide monitoring points,the similar failure points were obtained and the step deformation interval was obtained.The influencing factors of landslide deformation at different reservoir water levels were analyzed in detail,and the causes of landslide deformation were divided into three types:reservoir water drop induced deformation,rainfall induced deformation and reservoir water coupling rainfall induced deformation.The step information is extracted,and mathematical statistics,correlation analysis method are used to obtain the threshold value of outflow water,which is that the reservoir water drops 23 days at the rate of 0.6m/d;During the period of reservoir water level decline,the rainfall threshold was 50mm of the 8-day accumulated rainfall in the early 20mm of the rainfall,and 90mm of the 8-day accumulated rainfall in the early 35mm of the rainfall during the period of reservoir water level rise.(4)Numerical simulation analysis of Bazimen landslide based on deformation characteristics.By simulating the changes of seepage characteristics,displacement and deformation characteristics of landslide and slope stability under actual conditions and different reservoir water and rainfall conditions,the results show that the pore water pressure of the landslide front soil rises and falls with the reservoir water,while the pore water pressure of the landslide rear soil increases sharply with the increase of rainfall.Under the action of rainfall and reservoir water decline,the rear and front slopes first undergo deformation and gradually through,from local deformation into overall sliding,the front of the landslide is resistant to sliding,and the deformation of the slope below an elevation of152m is not significant.Stress concentration occurs in the middle of the landslide.The greater the rate of reservoir water decline(rise),the faster the stability coefficient of slope decreases(increases),and the worse(good)the stability of slope.The change of slope stability is subject to the water head difference between the lower water level in the slope and the reservoir water level.The sensitivity of landslide to rainfall is higher during reservoir water decline.The greater the rainfall intensity,the lower the landslide stability.Under the condition of reservoir water decline combined with no rainfall,10 year return period,and 50 year return period rainfall,the final stability coefficient of landslide is 1.047,1.041 and 1.039,respectively.Continuous rainfall will further deteriorate the landslide stability,and the final stability coefficient of landslide is 1.029 under the condition of reservoir water decline combined with continuous rainfall.(5)Revival mechanism of Bazimen landslide.Summarize the formation process and revival deformation factors of the Bazimen landslide,analyze the deformation characteristics and numerical simulation results of the landslide.The steep and gentle backchair structure of the landslide provided a good accumulation environment and free space conditions for the revival of the landslide.The strength of the slope is reduced when the reservoir water is soaked,and the landslide is revived and deformed under the combined action of hydrodynamic pressure and uplift pressure caused by the reservoir water falling. |
PDF Full Text Request