The Response Characteristics To Changing Water Level And Themechanism Of The Reactive Landslide In Three Gorges Reservoir Area

Since the impoundment of the Three Gorges Reservoir in 2003,especially in the early stage of impoundment,a large number of landslides have been reactived,With the reservoir water level maintained in 175m-145 m,there are few landslides sliding in recent years.One of the factors causing sliding of landslide is that the mechanical state of landslide rock and soil has been changed by reservoir water level,as a key factor of landslides,the effect of reservoir water level on slip soils is very significant.In recent years,the deformation of landslide is low level,the strength recovery of slip soils is one of the important reasons for improving landslide stability.This paper analyzes the deformation response law of landslides to reservoir water level change in Three Gorges Reservoir Area,and selects 2 slip soils of typical landslides.throughing triaxial test,consolidation test and shear test,there are further undersanding for deformation and intensity changes of the landslides' slip soils in the Three Gorges Reservoir Area during the process of reservoir water level filctuation.The results are as follows:(1)The reactivation deformation of the landslide in the Three Gorges Reservoir area is related to the operation stage of the water level:(1)From 135 m to the first 173 m during 2003 to 2009 in Three Gorges Reservoir Area,it will cause a large number of old landslides to revive,especially the decline of water level in 2007-2009 in the first stage of each high water level.Many landslides are deformation and have a high degree.(2)The landslides most have hysteresis when the water level drops,the hysteresis time is about 2 or 3 months,and the rainfall can aggravate the deformation of the landslides during the flood season.(3)From the second 173 m to 175 m-145 m after the flood season in 2009,the landslides have less deformation,and tend to be stable.(2)Based on the triaxial CSD test,the mechanism and characteristics of landslide deformation due to buoyancy weight loss are analyzed: When the water level rises,the weight reduction effect of the anti-slide section is obvious,the shear strain of the sliding strip is "jumping" plastic deformation,the volume strain is elastic deformation,the soil structure of the sliding strip is damaged and the strength is reduced,which shows the "jump" growth of the displacement curve;When the water level drops,the shear strain of sliding zone decreases,and the elastic shrinkage of the volume strain increases.The structure of the slip zone is slightly restored and the strength increases,showing that the displacement curve is basically unchanged.(3)By comparing the characteristics of the deformation response of the landslides of the Three Gorges Reservoir from 2003 to the flood season of 2009 and after the flood season of 2009 to 175m-145 m,the old landslide have a ability of adaptive adjustment.The old landslides are adaptively adjusted in two ways under the action of reservoir water level: because of the dry wet cycle and seepage erosion caused by the change of water level,the permeability coefficient of rock and soil is increased;The drainage consolidation and the compression of slope deformation caused by the dry wet cycle make the soil strength regeneration.(4)Through the consolidation and shear test of the sliding zone soil,it is found that the strength of the slip zone does have strength regeneration.Regenerative strength is related to water content and reconsolidation stress,The maximum regeneration rate of cohesion and internal friction angle of the OuTang landslide is 93.03% and 72.86% respectively,The maximum regeneration rate of cohesive force and internal friction angle of SanMashan landslide is 92.78% and 85.53% respectively.Through the residual strength,the strength of the cohesive force and the internal friction angle of the slipping soil is regenerated,the shear strength of the sliding zone soil is improved,and the stability of the landslide is improved.(5)The mechanism of strength regeneration of slip zone soil is analyzed by changing the microstructure of the shear surface.After reconsolidation,the void ratio decreases,the specific surface area increases,and the interaction between soil particles increases;The sand grains in the sliding zone can "lock" the shear surface and increase the friction strength;The cohesive force of the skid soil mainly cemented by clay minerals increased cohesion,and the grainy calcite dominated soil particles interlocked each other,which enhanced the friction strength;The strength of reconsolidation is due to the change of soil particle structure,and the strength of structure will change with the change of structure.