Study On Early Recognition For Potentially Loess Landslide

Loess mainly distributes in arid and semi-arid areas of China,with an area of 6% of the surface area of China.Because of its special origin,it is also known as the most easily eroded soil.And the number of loess-related geological disasters accounts for one third of the country.At the same time,these disasters also have many characteristics,such as many points,full range of types,strong concealment,obvious regional differences,and large difficulty of disaster prevention.At present,a lot of research has been done on the disaster-causing factors and mechanism of loess landslide and rich results have been achieved.But aiming at the failure modes and evolution process of loess landslide,and combining with new geoscience technology and new methods,an early identification method of potential potential hazards of loess landslide is established,and the unstable slope body is identified,discovered and warned in advance,which is of great significance for disaster prevention and mitigation in loess area.This paper solves the difficult problem of early recognition of potential loess landslides,and puts forward a technical method system for potential identification of loess landslides,which combines "geological identification" and "technical identification".They could capture the deformation characteristics and precursory information of hazards in the process of landslide formation from different spaces and scales.The potential loess landslide in study area is early recognized by combining the geological identification method with the "Space-Sky-Ground" multi-source stereo observation method,which could predict its hazard scope.The main results obtained in this paper are as follows.(1)The database of typical loess landslides in the Loess Plateau is established,and the basic conditions of landslide formation,deformation characteristics and basic evolution laws are analyzed.Combining with the geological-mechanical mechanism of loess landslides,four basic failure modes are revealed: loess collapse,landslides within loess,loess-bedrock interface landslide and loess-bedrock landslides.Based on its different mechanical behavior and disaster-induced factors,11 common failure modes are subdivided.Through the different identification factors established in different stages of evolution,the early identification map of potential loess landslide is compiled.The advanced identification index is established the initial identification index is established the state stage vulnerability identification method,the time-dependent deformation stage early identification method,the progressive failure state disaster identification method and the failure accumulation stage disaster identification method.(2)Through on-site geological survey and aerial survey of low-altitude photogrammetry,the engineering geological conditions of the study area are identified,the high-precision DEM of the study area is drawn,and the historical landslides are interpreted.The main types of loess landslides are clarified,and the spatial distribution law of seven sections of loess landslides in the two areas is revealed,the development characteristics of loess landslides in the study area are analyzed and summarized.On the basis of two main disaster-causing factors of groundwater level and stratum occurrence,four disaster-causing models of loess landslides are put forward,namely,loess bedrock type,loess flowslide,slide-collapse type and loess flow type.(3)By interpreting the high-precision remote sensing images in the past 50 years,the loess landslide database of loess landslide in Heifangtai terrace has been compiled,and the temporal and spatial evolution characteristics of Heifangtai loess landslide have been studied.Three laws of the temporal and spatial evolution have been summarized.Two landform identification criteria,i.e.the gully area on the edge of the plateau and the gap area of the landslide,are proposed.In the preceding 2015-2018 years,more than 30 new landslides have verified the practicability and accuracy of two landform identification criteria.Therefore,recognition method for potential loess landslide by high resolution satellite images is established.(4)The precision of closed-range photogrammetry is enhanced by arranging the basic control points and ground phase control points in the study area.According to the GPS monitoring results installed before aerial survey,the reliability and feasibility of low-altitude photogrammetric accuracy are verified.Through the reconstruction of a typical landslide process,the sliding process of loess flowslide is understood.The coefficient of volume expansion of loess flowslide is about 1.4.Through the spatial matching relationship between the distribution of cracks,sinkholes and disordered ridges in the cropland,and the new boundary of potential landslides was predicted.On this basis,through the last two three-dimensional point cloud difference calculation,the deformation area between 0.1-1 m is extracted,and many potential loess landslides in Dangchuan section are identified.Based on the results of "technical method" identification,the potential loess landslides are checked through local resident's survey and field investigation.New loess landslides occurred in February 2017,October 2017 and August 2018 verified the reliability of the early identification method for potential loess landslides by closed-range photogrammetry.(5)Based on geophysical prospecting,field test and spring outlet line monitoring,three kinds of geological identification indicators are summarized: surface cracks and disordered ridges,high and enriched areas of groundwater and critical water level of loess slope.Based on topography and landform,fracture development characteristics,slope deformation rate,groundwater characteristics,relationship between saturation line and loess thickness and landslide hazard characteristics,a comprehensive identification method for potential hazard points of loess bedrock type,shallow collapse type,loess mud flow type and static liquefaction type landslide is established.(6)Through the "Space-Sky-Ground" integrated technology identification method,DC#4 is identified as the potential loess landslide.Through a large number of investigations,besides itself characteristics of loess(cohesion C and internal friction angle ?),the water content(liquefaction coefficient of basement)of the movement path of the loess flowslide is the key factor affecting the movement distance of the landslide.Through statistical analysis on a large number of laboratory tests,the values of internal friction angle ? and value range of cohesion C of the loess are determined.And then through the inversion analysis of some landslide accumulation zone,determine the specific value of the cohesion of loess.The range of liquefaction coefficient of basement is determined by sample learning and inversion analysis of the accumulated range of actual movement of landslides that have occurred.Then the potential slide surface of landslide is fitted and the scale of landslide is determined by image interpretation and field investigation of DC#4.After the key parameters are determined,the forward analysis and prediction evaluation of the accumulation range of potential landslide motion can be realized by numerical simulation.The results show that potential landslides threaten highways and houses which are located at the toe of slopes.A method of forward modeling and hazard range prediction of loess flowslide are proposed,and quantitative risk assessment is carried out accordingly.