Study On Geomorphologic Mapping Of Loess Landslides In Different Geomorphic Unit

In recent years,loess landslides on the Loess Plateau are occurred frequently because of extreme climate and human engineering activities,which threatens the major project construction and the safety of people's lives in western region,the prevention and treatment work is imminent.Therefore,study of the start-up process and movement characteristics of disasters plays an important guiding role in prevention and control.However,the evolution of modern landforms on the Loess Plateau is one of the main controlling factors of landslide hazard,it is mainly manifested in the development degree,type,scale mechanism of landslides vary with different landform characteristics.Although there are abundant research results on the mechanism of Loess landslide,the study on Geomorphologic Mapping in guiding prevention and treatment is not enough,and few studies on the mechanism of loess landslide under different geomorphic unit.In this paper,chose Baxie River Loess beam in Dongxiang country,Heifangtai Loess Tableland in Yongjing county,and Laolang Erosion Gully in Lanzhou city of Gansu Province as study areas,by interpreting historical remote sensing images,combining field surveys to map the land slides in those study area,counting the number of landslides,investigating the types of landslides,expounding the distribution of landslides,and discussing the influence of topography on the distribution of landslides.And,the engineering geomorphology map before and after sliding of typical landslide in the study areas based on historical remote sensing imagery and field survey,using ArcGIS to extract the topography,hydrogeological conditions and accumulation characteristics before and after sliding based on high-precision DEM,so as to analyze the startup process and motion characteristics of those typical landslides.Research has made the following main results and conclusions:By interpreting historical remote sensing images of the Baxie River Basin,it is found that the landslides in the study area are characterized by high degree of development,many types,complete in size and scale and high risk of disasters,zonal distribution along river and gullies,and asymmetric,uneven distribution in the upper,middle,lower and the two sides of river,and the most developed landslides in the middle and lower river and the north bank.Sale mountain landslide as the most typical catastrophic landslide in the study area,based on DEM Spatial Analysis and historical remote sensing image interpretation before and after sliding,and field investigation,establish a geological model before and after event,results show that water is the leading cause for it initiation and movement.Firstly,the surface and subsurface runoff are flow converge the slope foot before the event,together with the reservoir water storage to raise the groundwater level of the slope,soaking and softening the bedrock,resulting in long-term deformation of the slope,and the deformation speed increases with time.Secondly,bottom liquefaction is the direct cause of its high-speed movement.Mapping landslides by interpreting Google Earth historical images and field surveys,found that Laolang Gully only developing small and medium-sized shallow loess landslides,which are symmetric distribution in the slope of the gully.Through the detailed engineering landscape mapping,analyzing the mechanism and movement model of these landslides,it is found that the terrain at the back of the rotational landslide is obviously inclined to the main scarp,while the surface of the translational landslide is straight,and the collapse sliding down vertically;also found that joint is one of the main controlling factors of landslide evolution,which not only controls the perimeter of landslide,but also the formation of sliding shear plane along the structural joint surface,and the precipitation is infiltrated along the joints and sinkholes,which strongly changes the underground seepage conditions of the slope and affects the stability of the slope.Mapping landslides and Tableland border of Heifangtai by interpretation of historical remote sensing images and detailed field surveys,found that 87 landslides,which characteristic by large frequency,high density and serious disaster damage,and the distribution of types is spatially segmented,the number and size have an increasing trend in time.Erosion Tableland border year by year,the maximum regression 182.5m.For mechanism,agricultural irrigation raises the groundwater level of Tableland,and discharges it along the relative aquifer for a long time,so that the rock and soil in the drainage path are saturated and softened,desalted and the shear strength is reduced,and the overlying rock mass slides down the weak zone form a landslide.The Geomorphologic Mapping of Landslides is to investigate the lithology,geological structure,topography and hydrogeological conditions of the landslide before occurred so that analyze the starting mechanism of landslides.And investigating the characteristics of accumulation so that inverse analysis motion process of landslides.In this paper,the method based on historical remote sensing image interpretation,spatial analysis of DEM data,and laser range finder to map Engineering geomorphology of loess landslides and the landslide disaster model,can provide basic data and theoretical basis for risk assessment,early warning and prevention of landslide hazards in the study area.Also provide reference methods for the distribution and cause investigation of landslides in the same or similar geological background areas.