Resurrection Mechanism And Stability Analysis Of The Ancient Landslide Of Aniangzhai In Danba County

On June 17,2020,affected by extreme heavy rainfall weather,Aniangzhai ancient landslide located on the left bank of Xiaojinchuan River in Danba County,Sichuan Province,Because of the sudden massive mudslide in the Meilonggou which opposite the main river channel,blocking the Xiaojinchuan River,resulting in a high water level and scouring the foot of the ancient landslide body,resulting in the resurrection of a large area of the Aniangzhai ancient landslide,forming a Meilonggou mudslide blocking the river-resurrection of Aniangzhai ancient landslide-flash flood(mudslide)in the Xiaojinchuan River disaster chain.Seriously threaten the safety of upstream coastal towns and downstream Danba County,causing a great threat to the safety of life and property of local residents.In this paper,on the basis of data collection,the basic characteristics of the ancient landslide were identified through on-site investigation,unmanned aerial survey and physical prospecting.And using engineering analogy empirical method,field test and 3D simulation software,the development characteristics and stability of the ancient landslide were analyzed in detail.The following conclusions were drawn.(1)The ancient landslide surface gravel soil cover is thicker,the depth in the front edge section of the landslide may exceed 100m,and the depth in the middle and back edge sections of the landslide is between 60～80m;the burial depth of the soft sliding surface of the ancient landslide is presumed to be 60～80m,the ancient landslide is mainly dominated by kilometre rock and slate,and the burial depth of bedrock is presumed to be below 100m.(2)The ancient landslide of Aniangzhai has a resurrection area of about 0.62km~2,its longitudinal length is about 650～950m,and its transverse length is about 600～850m.The resurrection body can be divided into four areas:Ⅰarea(leading edge landslide area),Ⅱarea(middle bulge deformation area),Ⅲarea(upstream side pull-out area),Ⅳarea(downstream side pull-out area).(3)Continuous rainfall weakened the nature of the ancient landslide geotechnical body,and the local blockage caused by the rising water level of Xiaojinchuan River and the debris flow of Meilonggou,and the scouring of the foot of the slope directly led to the resurrection of the ancient landslide.The resurrection mechanism is divided into three stages:leading edge slip,traction deformation and compound sliding(pre-drafting in the early stage and pushing in the later stage mainly).(4)The simulation results show that under the self-weight condition,the overall displacement of the middle and rear part of the landslide is the largest,and the left and right boundary areas of the landslide show large lateral displacement,and the deformation is dominated by shear damage.Under the rainfall condition,the landslide displacement increases and the stability decreases.(5)The stability calculation results show that the resurrection landslide is in an unstable state under self-weight conditions,and in an unstable state under both heavy rainfall+flood level and seismic conditions,and its leading edge has a high probability of continuing local landslides.The prevention and control of the resurrection body of the ancient landslide in Aniangzhai can be designed according to the idea of"water flowing back to the trough,river emptying,dike and road combination,backfill and back pressure".