Morphological Characteristics And Evolution Of Irrigation Induced Loess Landslide

Large scale agricultural irrigation causes frequent landslides on the edge of loess tableland,causing serious casualties and farmland damage.In order to study the morphological characteristics,evolution process and evolution model of irrigation induced loess landslides,this paper chooses Heifangtai landslide group in Yongjing,Gansu Province and Jinghe south bank landslide group in Jingyang,Shaanxi Province as research objects.The historical remote sensing images of the study area are collected,and the change process of landslide morphology in different periods is compared.The high-resolution positive photographic images and topographic data of these landslides are obtained,the morphological parameters of landslides are extracted,and the morphological characteristics of landslides are analyzed.The evolution process of landslide is summarized,and the evolution mechanism of irrigation induced loess landslide is discussed.The conclusion is as follows:(1)The morphological data of 45 landslides in the study area were obtained by UAV photogrammetry technology.The plane,section and three-dimensional shape parameters of landslide are extracted,and the shape characteristics of irrigation induced loess landslide are summarized.The statistical results show that the aspect ratio of this kind of landslide is concentrated in 1.6-2.0,the slope range is mainly 40°-50°,and the slope type is mostly concave.The fractal calculation results show that the slope type,slope,slope height,loess thickness parameters of irrigation induced loess landslides have complex relationship with landslides,and have greater impact on landslides.(2)The comparison results of historical remote sensing images in the past 40 years show that the evolution of landslides has typical multi-stage characteristics.The new and old landslides overlap each other,and the landslides continue to erode into the interior of the tableland.The retreat areas of Heifangtai and Jingyang South tableland are 5.1×10~5m~2and 8.1×10~4m~2 respectively.The results of point cloud difference obtained by multi-stage UAV photogrammetry show that the evolution law of different parts of the landslide is different.The slip source area of the landslide is usually concave.The back edge of the landslide retreats to the tableland,the angle of the main scarp increases continuously.The shape of the middle part of the landslide is related to the original terrain slope,and the area with the largest deformation of the slip slope is usually in the slip source area.(3)The rise of groundwater level caused by irrigation is the main reason for the high occurrence of landslides.The groundwater is affected by the effect of freezing and stagnant water,and the occurrence of landslides is obviously seasonal.The pore pressure of concave slope is larger,the suction between loess particles is lower,and the possibility of instability is the greatest.The evolution model of irrigation induced loess landslides can be divided into irrigation stage,sliding stage,Sliding expansion stage and overall sliding stage.