Resurrection Mechanism And Stability Evaluation Of Dayuanbao Landslide In Xuanhan County,Sichuan Province

Due to Controlled by the special lithological association and the structure of the slope,the red bed area was generally an area where the landslide hazard happened easily.The Dayuanbao landslide in Xuanhan County,Sichuan Province was an ancient landslide developed in a flat red bed.It was during the heavy rain in September 2004 when the landslide experienced obvious creeping deformation,resulting in seriously threatening the lives and properties of the residents living on it.The research on the resurrection mechanism of the ancient landslide and the evaluation of the stability of the landslide can provide a scientific basis for the prevention and control of the landslide.In this paper,it analyzes the influential factors and formation mechanism of the ancient landslide based on the identification of the basic geological conditions and the basic characteristics of the landslide area;analyzes the deformation and resurrection mechanism of the landslide and researches on the resurrection mechanism of the landslide by adopting the numerical simulation method according to the deformation characteristics and deformation factors of the landslide;meanwhile,it adopted the limit equilibrium method to evaluate the overall and local stability of the landslide in order to propose the prevention and control measures of the landslide.Here are the main research results obtained.(1)Dayuanbao landslide developed in flat bed slope structure,the plane shape of which is shown as an irregular dustpan.The relative height difference of the landslide area was between 78?59m,and the maximum longitudinal length of the landslide was 270m.The middle and rear part of the sliding body is thicker in the longitudinal direction,with a thickness of 5.0?12.0m.While the thickness of the front part was relatively small,with a thickness of 4?10m;in the landscape orientation,the two sides were thin while the middle part is thick,with an average thickness of about 7m,and the square volume was about 64.4×104m~3.It was a medium-sized landslide,and the main sliding direction of the landslide was 39°.(2)After analyzing the development characteristics and formation conditions of the ancient landslides,it has analyzed various factors that caused the slopes to slide systematically.The formation of the ancient landslides was mainly controlled by the flat bed slope structure and the soft and hard lithological association.Affected by the rainfall,the rock began to gradually undergo bedding creep along the weak mudstone layer,resulting in the slope body loses its stability in the damage patterns of"slip-crack"under the action of the dynamic and static water pressure and the decreased shear strength of weak mudstone layer.(3)The landslide was resurrected due to the continuous heavy rainfall happened on September 3,2004.It was mainly caused by the comprehensive function of the unfavorable geological environmental conditions and the continuous heavy rainfall.The lower part of the landslide area is mostly the platform cultivated land.The rainwater was concentrated in the middle and front part,for which it was difficult to drainage.The surface quaternary soil layer structure was loose,which was conducive to rainfall and the surface water infiltration.Because of the continuous heavy rainfall,the rainwater gradually infiltrated inside the slope body,resulting in forming the hydrodynamic pressure and floating force inside the slope.And finally,due to the attenuation of the shear strength of the sliding zone and the combined action of the groundwater,the ancient landslide deformed and damaged to form a"creep-crack"type landslide.(4)It adopts the two-dimensional seepage numerical simulation to reproduce the seepage change process of the ancient landslide affected by the heavy rainfall 4 days before the deformation and failure of the ancient landslide.Due to the heavy rainfall,rainwater flowed from top to bottom,first it saturated at the base cover interface at the front edge of the slope.The soil was saturated to form a transient saturated seepage field.With the rainfall lasted,the saturated area moved from the front edge of the slope to the middle and rear of the slope along the base-cover interface.And then the water level continued to rise and the pore water pressure gradually increased,which caused the stability of the ancient landslide was continuously reduced.After the coupling analysis of the seepage field and stability of the strong deformation zone,it showed that under the action of the heavy rainfall,the stability of the strong deformation zone has changed significantly,and the stability gradually decreased,staying at an unstable state.(5)FLAC3D numerical simulation analysis results showed that under the action of the rainfall,the displacement mainly happened in the front part of the ancient landslide body,and the deformation in the rear edge was small.The displacement occurred above the base-cover interface.The maximum displacement was 2.05m,locating in an area with an elevation of about 982m(that was,the rear edge of the strong deformation zone).The forward displacement gradually decreased,with the minimum displacement of the front edge of 0.2m,which was basically consistent with the actual displacement and deformation of ancient landslide deformation.(6)Based on the qualitative analysis,it adopted the limit equilibrium method to calculate and analyze the stability of the entire landslide and the strong deformation zone under the natural and heavy rain conditions.The calculation results showed that the entire landslide and the strong deformation zone were basically at a stable condition under the natural conditions,while at an unstable condition under the heavy rain conditions.(7)Based on the resurrection mechanism,deformation characteristics and stability evaluation of ancient landslides,it has proposed a targeted treatment plan for the landslides.The treatment project adopted the"anti-slide pile+intercepting drainage ditch+crack ramming and filling",and checked the stability of the landslide after treatment,the calculation results of which has met the treatment requirements.