Simulation Study On The Process Of Impact Easily-eroded Terrace Layers Of Loess Landslide At South Jingyang Plateau,China

Loess landslide hazards have occurred frequently in south Jingyang plateau since 1980s.The majority of these loess landslides have the kinetic characteristics of high speed and long distance.Additionally,some significant geological phenomena could be caused by the impact of loess landslides on easily-eroded terrace layers during the corresponding kinetic process.Therefore,the loess landslides in south Jingyang plateau were employed as research objects in this thesis,and the kinetic characteristics of typical landslides were acquired by field investigation.Furthermore,series of physical model experiments were designed and implemented in laboratory.In this way,the digital models of landslide deposits in the physical model experiments were established by 3D laser scanner,and the data of landslide kinetic characteristics were obtained and extracted using high-speed camera.Then,the effects of xvarious conditioning factors on landslide deposit areas were discussed,and the characteristics of easily-eroded terrace layers under landslide impact were analyzed as well.Meanwhile,the kinetic process of a typical loess landslide was simulated using particle flow code(PFC).Based on the field investigation,laboratory experiments and numerical simulation,some results and conclusions were obtained and as follows:(1)Landslides in this study area spread along south Jingyang plateau with zonal distribution features.There exist four obvious landslide groups,respectively,Jiangliu landslide group,Shutangwang landslide group,Zhaitou landslide group and Miaodian landslide group.Through the investigation of Ximiaodian landslide,the easily-eroded terrace layers could be impacted during landslide kinetic process,and the corresponding phenomena include repetition and disorder of terrace strata,liquefaction of slip zone soil,sand flowing on surface and strata leaping around the front of landslide.(2)According to the results of laboratory experiments,the cushions could dramatically reduce the motion distance of landslides and the length of landslide deposits when the thickness and volume of landslide deposits increase.Besides,the influence of cushions on width of landslide deposits was not significant,and the disaster scope of landslide was enlarged generally.Through analyzing the results of laboratory experiments and numerical simulation,the landslide deposit region formed by the landslide impact on easily-eroded terrace layers could be identified into impacting-replacing zone,sliding-scraping zone and depositing-napping zone.Moreover,the shape of landslide deposit varied with the increasement of sliding angle,mainly including changes of geometry of uplift belt and the corresponding position with maximum thickness.(3)On the basis of laboratory experiments and numerical simulation,the kinetic process of landslide without cushions could be divided into three stages:accelerating stage,decelerating stage and slowly stopping stage.The kinetic process of landslide with cushions could be arranged into four stages:accelerating stage,decelerating stage,slightly accelerating stage and slowly stopping stage.(4)Some obvious phenomena such as strata replacing,rolling,reversing and rubbing could be observed in the section diagrams derived from field investigation,physical model experiments and numerical simulation.In terms of the laboratory model experiments,the position of uplift belt was in accordance with the zone where strata replacing occurred.In the neighbors of uplift belt,the strata sequence of cushion was disturbed.Concretely,the layers of cushion were completely rolled and reversed,and the sand layers in part of cushion which was not scraped could be rubbed under the effects of forward thrust force.