| China has the largest and most concentrated loess in the world,accounting for 4.9% of the loess area in the world.They are mainly distributed in semi-arid areas with sparse rainfall throughout the year.Therefore,agricultural development in the loess area requires a lot of irrigation,but many years of unreasonable irrigation methods changed the groundwater balance in the loess area and induced a large number of loess landslide disasters.In Heifangtai,Yongjing County,Gansu Province,due to more than 50 years of agricultural irrigation,the groundwater level has risen and more than 200 landslides have been induced,seriously threatening the safety of local people 's lives and property.Monitoring and early warning of loess landslides is an effective disaster prevention and risk avoidance measure,and monitoring and early warning of loess landslides needs to be based on the scientific results of early identification.Therefore,the refined early identification of loess landslides has important guiding significance for disaster prevention in this area.This article compares and analyzes the data of multi-stage ground fissures,micro-deformation of plateau,deformation of landslide accumulation body and buried depth of groundwater level before and after the sliding of 10 landslides in Heifangtai Dangchuan section from 2015 to 2019 and draws on the comprehensive identification criteria for early identification of the Heifangtai loess landslide based on these four types of signs.First,visually interpret the UAV high-definition image statistics of the ground fissure data of the Dangchuan section from 2015 to 2019,use RTK survey points to conduct on-site verification,analyze the temporal and spatial distribution characteristics of ground fissures,and draw early criteria for landslide identification based on ground fissures;Secondly,differentiates 15-phase UAV three-dimensional texture mesh to identify the small deformation of the edge of the plateau and the deformation of the slope foot accumulation due to the discharge and erosion of groundwater,and analyze the correspondence between the deformation characteristics and the type of landslide,and draws the criteria for early identification and identification of landslides based on the small deformation of the edge and the deformation of landslide accumulation body;Thirdly,use the high-density resistivity method to detect the buried depth of the groundwater level in the Dangchuan section,identify the distribution characteristics of the groundwater in the plateau,and obtain the early identification criteria for landslides based on groundwater;Finally,through the analysis of the four types of identification criteria,the comprehensive identification criteria for the early identification of the Heifangtai loess landslide are concluded,and provides guidance suggestions on the deployment of monitoring and early warning instruments.(1)A total of 842 ground fissures were developed in the Dangchuan section of Heifangtai from 2015 to 2019,with a length of more than 15,000 m,distributed within 140 m from the edge of the plateau;ground fissures evolved from west to east,corresponding to the landslide evolution In the development of landslides,ground fissures go through four stages: emergence stage,development stage,penetration stage,and extinction stage;according to the genetic mechanism,ground fissures are divided into tensile fractures and collapsible fractures,and their characteristics have the following indications for various types of landslides: Collapsing cracks with a plateau margin of 90-140 m indicate medium loess flowslide;tensile fractures with plateau margins of less than 40 m indicate loess slide and small loess flowslide,where the distribution series is less than 3 linear extensions Tensile cracks indicate the former,and arc-shaped tensile cracks with a grade greater than 4 indicate the latter.(2)The difference between the deformation variables based on the differential identification of the three-dimensional texture grid of the UAV and the deformation variables monitored by the GPS is in the centimeter level,and can be used to analyze the deformation of the slope body.The small deformation of the edge of the Dangchuan section is within 1m,and the deformation is concentrated within the range of 100 m from the edge of the plateau.Its characteristics indicate to the landslide: Deformation features with obvious local deformation and clear deformation boundaries indicate loess slide.Deformation features with deformation coverage area exceeding the tension crack distribution area indicate medium loess flowslide,but no obvious deformation characteristics for small loess flowslide.(3)Under the action of groundwater excretion,landslides in the Dangchuan section are prone to erosion and deformation of slope foot deposits,and the erosion thickness is 0 ? 3m.This process can increase the slope foot slope and thus affect the stability of the slope body.Its indication significance for landslide is: There is no obvious erosion and deformation characteristics on the front edge accumulation body for loess slide and medium loess flowslide.For 3 small loess flowslide,the erosion and deformation characteristics are obvious.The average slope angle before erosion is 40 °,33 °,35.5 °,the corresponding slope becomes 60.3 °,54.6 °,51 ° after the erosion occurs,so the erosion deformation characteristics of the accumulation body indicate small static liquefaction landslide,and the slope angle of 50 ° is the criterion threshold of this standard.(4)The high-density resistivity method can be used to reveal the buried depth of the Heifangtai groundwater table.This method reveals that the buried depth of the groundwater level in the Dangchuan section of the Yuanbian fluctuates within 9-25 m,showing a trend of increasing buried depth from west to east.There is local water level swell phenomenon,and the height difference between the swell height is 5m to 10m;analysis of the corresponding relationship between the swell height feature and the landslide shows that the local swell height of groundwater indicates loess slide and medium loess flowslide,while small loess flowslide has no characteristics of groundwater height.(5)Through comprehensive analysis of the four types of signs,the comprehensive identification criteria for early identification of the Heifangtai loess landslide can be obtained: firstly,the ground fissures are set as the initial screening criteria,and the range of potential hidden dangers of various types of landslides is initially identified;secondly,using the small deformation of the plateau and the erosion and deformation of the landslide accumulation as a detailed investigation standard,to identify the deformation of the plateau in detail and determine the type and scope of potential hidden landslides;again,using groundwater as a supplementary identification criterion to identify the interior of slopes without obvious deformation on the surface;finally,organically combines the four types of features identified,comprehensively analyzes the corresponding landslide features.The early recognition results have guided the deployment of monitoring and early warning instruments,and have successfully warned three landslides in the Dangchuan section of Heifangtai,demonstrating the good application of the standard. |
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