| The Jinsha River Tectonic Zone is located in the eastern part of the Tibetan Plateau.It is characterized by deep river valleys,complex lithology,frequent earthquakes,strong internal and external dynamics,and paleo-landslide development.In recent times,a combination of extreme weather conditions and human activities hava led to an increase in the occurrence of disasters caused by the resurrection of ancient landslides,resulting in significant damage.This paper specifically focuses on the Chashushan ancient landslide,situated in Batang County,western Sichuan Province.Through the utilization of various methodologies including data collection,remote sensing interpretation,unmanned aerial surveys,field investigations,laboratory tests,numerical simulations,and model testing,this research aims to investigate the spatial structure,deformation characteristics,factors influencing deformation,and the evolutionary process of the Chashushan landslide.Finite element numerical simulation software is employed to analyze the changes in seepage and displacement fields of the landslide under rainfall and concentrated infiltration conditions.The study also employs the continuous medium inversion method to analyze the movement process of the unstable resurgent landslide at Chashushan.By examining typical patterns of paleo-landslide resurgence in the region,the research suggests that water and fractures play crucial roles in the resurgence of large mounded paleo-landslides in the area.Furthermore,physical model tests are conducted under different media infiltration conditions to explore the influence of geotechnical media and seepage channels on the resurgence of large mounded paleo-landslides.The main conclusions and findings of this study are as follows:(1)The Chashushan landslide is characterized by a longitudinal length of approximately 620m and a transverse width of about 400-520m.The slide body is approximately 30m thick,with a volume of 720×10~4m~3 and a slide distance of 20m.The slope body exhibits clear deformation characteristics and can be divided into seven distinct zones.Based on the analysis of landslide deformation and engineering geology,the Chashushan landslide can be categorized into seven deformation zones:trailing edge extension zone(Ⅰ),central traction damage zone(Ⅱ),lateral slip zone(Ⅲ),left traction damage zone(Ⅳ),slope debris flow zone(Ⅴ),diagonal pull damage zone(Ⅵ),and front edge strong displacement zone(Ⅶ).(2)The Chashushan landslide serves as an exemplary case of a landslide that demonstrates coupled internal and external dynamics.Multiple factors contribute to the formation of the Chashushan landslide,with the lithology of the strata being an internal factor influencing the landslide resurgence.The interaction between rainwater and fracture creep crack results in increased slope deformation and damage to the channel at the rear edge of the landslide.Extensive rainfall and canal water infiltrate through the dominant seepage channel formed by creep slip and tensile crack,leading to landslide instability and resurgence.The initial stage of landslide deformation occurs at the central Batang fault crossing position.The coupling effect of fracture creep crack and rainfall leads to the development of slope surface cracks and the disruption of the trailing channel,while the infiltration of channel water triggers large-scale landslide sliding.(3)During rainfall,rainwater infiltration is more uniform and less likely to penetrate into the deeper layers of a landslide.As a result,the shallow surface layer of soil experiences deformation.The coupling effect of rainfall infiltration and the middle crack aggravated the deformation in the middle of the landslide and pulled the upper sliding body to further deformation,leading to the tensile cracking of the rear edge and the miscutting of the canal.The infiltration of canal water along the tension crack of the rear edge led to the weakening of the mechanical properties of the landslide sliding zone,resulting in the instability and failure of the landslide.(4)The movement process inversion of the Chashushan landslide indicates a slow resurrection with low movement speed.The landslide took a total of 50 seconds to move,covering a distance of 46m at a speed of9.8m/s.The movement distance of the landslide centroid is approximately130m,covering an area of 23.4×10~4m~2.The simulated accumulation thickness is greater than the measured accumulation thickness,and the total coincidence factor of the numerical simulation is T=74.7%.(5)The rainfall threshold for landslide instability and failure is influenced by the type of seepage.In the case of fracture seepage,the rainfall threshold is significantly lower compared to pore seepage.Pore seepage leads to erosion damage at the slope’s foot during prolonged rainfall,followed by localized damage at the leading edge.Conversely,fracture seepage causes saturation of the central part of the slope first,primarily due to the dominant infiltration channel in that area,resulting in slip damage.Under both seepage conditions,the pattern of landslide instability is progressive and retreats.In the case of pore seepage,the process of slope instability involves toe erosion,followed by localized progressive damage at the leading edge.For fracture seepage,the process of landslide deformation instability includes creep slip pulling,local slip,local damage at the leading edge,and progressive slide damage. |
