Study On Hysteresis Effect Of Reservoir Colluvial Landslide’s Deformation

Colluvial landslide,a type of landslide that occurring in the loose colluvial layers of the quaternary,mostly occur in the front of mountains and on both sides of river valley.and have distribution widely,high frequency of deformation damage,and hazard seriously.Due to the internal factors,the unique geological environment characteristics,and external factors such as reservoir filling,a large numbers of colluvial landslides were developed in in Three Gorges Reservoir area.Baijiabao landslide in Zigui County was selected as a typical colluvial landslide in the Three Gorges Reservoir area to study the deformation hysteresis effect of colluvial landslide under the effect of reservoir water level and rainfall.The research results have important application value,for example,the alerts of landslide hazard are released correctly and the effective measures are adopted.The data of Baijiabao landslide in Three Gorges Reservoir area,including geological environmental conditions,basic characteristics of landslide,monitoring information,macroscopic geologic phenomenon was selected to analyze the factors,which affect the landslide deformation.Based on the Baijiabao landslide,the experiment of physical model was designed,which includes material of modeling experiment,monitoring program and design of working case.According to the data from the physical model test under different working cases,the deformation hysteresis effect of colluvial landslide was analyzed under reservoir water level deceasing and rainfall.Finally,numerical simulation is used to study the deformation hysteresis effect of colluvial landslide under permeability coefficient of sliding mass.The research contents and results are as follows:(1)According to field investigation and analysis of professional monitoring data of landslide,it is clarified that the decline of the reservoir water level and rainfall are the main inducing factors affecting the deformation of Baijiabao landslide.(2)Based on similarity theory and similar material tests,the scale of landslide deformation hysteresis physical model test is determined and the ratio of similar materials to different rock and soil masses:(1)Determine the geometric similarity ratio between the prototype and the model,and the size of the model is 5.5m×2.3m×0.8m.(2)The sliding bed is made of masonry and cement mortar;The sliding belt adopts glass beads,talcum powder and water in the ratio,and the mass ratio is 8:1:1;The sliding body is made of fine sand,clay and water,and the mass ratio is 6:3:1.(3)According to the variation of water level in the Three Gorges Reservoir area and the rainfall data table of Baijiabao landslide in Zigui County,the physical model test of landslide deformation hysteresis was designed,which took two factors into consideration.One is the decline rate of the reservoir water level,including 0.6m/d,1.2m/d and 1.8m/d while another is rainfall intensity involving 20mm/d×3d,45mm/d×3d and 70mm/d×3d.There are four observed profiles in model test monitoring system.There are four sensor in each of observed profiles,which can record the change of moisture content,soil pressure,pore water pressure and surface displacement during the decline rate of the reservoir water level and rainfall.(4)It reveals the variation law of lag time of landslide deformation in reservoir bank accumulation layer under the action of different reservoir water level falling rate and rainfall intensity:(1)The greater the rate of decline of the reservoir water level,the shorter the lag time of the landslide surface deformation;Compared with the lag time of surface deformation when the reservoir water level drop rate is 0.6m/d,when the reservoir water level drop rate is 1.2m/d,the lag time of the landslide front and central surface deformation is shortened by 4.75d-4.89 d,and the trailing edge surface deformation The lag time has been shortened by 7.62d;Compared with the deformation lag time when the reservoir water level drop rate is 1.2m/d,when the reservoir water level drop rate is 1.8m/d,the lag time of the landslide front and central surface deformation is shortened by 0.42d-1.17 d.The lag time is shortened by 0.59d;The scope of influence of different reservoir water level drop rates on Baijiabao landslide deformation is mainly distributed below the slope elevation of 228 m.(2)At a depth of 21 m in the sliding body,when the rainfall intensity is 20mm/d,the lag time of the pore water pressure change is 13h;When the rainfall intensity is 45mm/d and 70mm/d,the lag time of pore water pressure change is 5h.At the position of 38 m buried in the sliding body,when the rainfall intensity is 20mm/d,the lag time of pore water pressure change is 18h;When the rainfall intensity is 45mm/d and70mm/d,the lag time of pore water pressure change is 11 h.The impact of different rainfall intensities on the deformation of Baijiabao landslide is mainly concentrated from the slope elevation of 175 m to the rear edge of the landslide.(5)Based on numerical simulation,the influence of different landslide permeability coefficients on the lag time of landslide deformation is explored: When the permeability coefficient of the slide body is 0.2m/d,the water in the slope body will seep out slowly,and the lag time of the total water head change in the slide body under this working condition is 6d;When the permeability coefficient of the sliding body is 1.9m/d,the lag time of the total water head change in the sliding body is 2-3d;When the permeability coefficient of the sliding body is 3.6m/d,the lag time of the total head change in the sliding body is 1d.