Rainfall-induced Shallow Landslides Susceptibility Assesment Based On TRIGRS Model In Jiaochangba Valley

Rainfall-induced landslides account for 60% of happened landslides and are the major types of geological disasters in China.Qinzhou district located in the southeastern part of Gansu province is in the transitional zone between the West Qinling Mountains and the Loess Plateau.The southern Niangniangba town is most located within the Lizi garden in the Xiaolongshan forest region with the pretty vegetation coverage.It is generally considered that high vegetation coverage areas are not prone to shallow landslides,however,during June to July in 2013 the continuous heavy rains led to various geological disasters in the area.There were 6,142 new shallow landslides in Niangniangba town induced by rainfall,which were mainly distributed in the areas with dense faults,weak lithology and high human activity.A large number of shallow landslides have caused huge negative impacts on the production and life of the people in the area.Therefore,strengthening research on landslides in the area will help to further understand the formation mechanism and distribution pattern of rainfall-induced shallow landslides in high vegetation cover areas.At the same time,using the TRIGRS model to carry out landslide susceptibility evaluation can provide theoretical support for the prevention and reduction of landslide disasters in the region,which has strong scientific and practical value.This paper first analyzes the basic characteristics of rainfall-induced landslides in Niangnianba town and then selects the typical gully,Jiaochang valley as a simulated experimental area for landslide susceptibility evaluation.On the basis of detailed field survey data and laboratory tests,a TRIGRS model was used in conjunction with GIS to simulate the landslide susceptibility of the Jiaochang valley under different rainfall conditions,landslide susceptibility grade zoning maps under different rainfall intensity were made based on the evaluation results,and then the evaluation results were verified using historical landslides in the ditch.The main conclusions of this paper are as follows:1.The main features of the rainfall-induced shallow landslides in southern Qinzhou area are:The landslides are mainly distributed on the dense slopes of vegetation,mainly are shallow landslides.The distribution of landslides is greatly affected by faults,the closer to the fault,the greater the landslide distribution density and area.Landslides are mainly distributed on slopeswith slopes of 15 to 35°.The more concentrated the regional distribution of landslides,the greater the impact of human activities.2.Based on the TRIGRS model,the susceptibility to landslides under different rainfall intensity was studied in Jiaochang dam.The evaluation results were divided into four levels:high-yield area,medium-to-easy area,low-prone area and relatively stable area according to the degree of proneness.Specifically the evaluation result is: When the study area is not affected by rainfall,only 4% of the area is in an unstable state.When the rainfall intensity is 10mm/h,the unstable area rises to 18%,and the low-risk area grows significantly,which up to 15%.When the rainfall intensity is 15mm/h,the unstable area further rises to 40%,of which the low-prone area accounts for 25% and the medium-prone area is 12%.When the rainfall intensity is 20mm/h,53%of the areas in the study area are in an unstable state,the high,medium and low-prone areas account for 8%,18% and 27% respectively.At this time,75.86% and 20.69% of the historical landslides respectively landed in the high-prone areas and the mid-prone areas.This is consistent with the actual rainfall intensity and occurrence of landslides in the study area during the “7.25”incident,indicating that the results of this evaluation are scientifically reliable.3.In order to further explore the causes of the landslide differences between the shade slope and the sunny slope in the study area,the slopes,soil thickness,and vegetation coverage of the two slopes were further analyzed and compared.It was found that in the same geological environment,sunny slopes with steep,thick soil layers and artificial forests are more susceptible to landslides than shady slopes.