| Landslides are one of the most common and widely affected geological hazards in China.And rainfall is an important factor inducing landslides.Especially in the fragile Loess Plateau,rainfall-induced landslides are particularly serious,causing huge casualties and property losses.In order to avoid the occurrence of landslides and minimize the losses caused by rainfall-induced landslides,the potential landslide zone should be identified as far as possible.It is one of the most effective methods to find the potential landslides zone by susceptibility and hazard evaluation of landslides,which is also the basis for hazard governance and avoidance scheme.The study area are located in Qin'an County,with typical loess hilly landform.This study evaluated the susceptibility of rainfall-induced landslides,and carried out the dynamic hazard evaluation of the rainfall-induced landslides.First,based on the existed landslide risk evaluation system,the landslide attribute was extracted and digitalized by field investigation and remote sensing interpretation.A complete regional rainfall-induced landslides database was established.Then the analysis of landslide database was performed to discover the distribution characteristics and development pattern of the rainfall-induced landslides,and to analyze the influential factors of the landslides in the study area.Through determining influential factors and establishing appropriate evaluation index system,the information value model was used to realize the classification and quantification of each influential factor of landslide.Based on ArcGIS,rainfall-induced landslide susceptibility was evaluated.The obfuscation matrix was used to test the accuracy of the susceptibility evaluation.Finally,in order to meet more accurate landslide evaluation,time scale was introduced.Dynamic hazard of rainfall-induced landslides was evaluated based on physical mechanics and space-time scale.The dynamic hazard evaluation was realized through the three steps,namely theory model establishment,model programming development and model parameters acquisition.By a series of field investigations,data collection and analysis,theoretical deduction and programming development,the following results was obtained:(1)Based on the Information Value Method,rainfall-induced landslides susceptibility evaluation was performed.Through the preliminary data collection and field investigation,the detailed data of the landslide in the study area was obtained,and the spatial database of the landslide was established.The evaluation index system of landslide susceptibility considering 7 main factors,namely lithology,slope angle,slope aspect,relief,distance to stream,distance to branch and vegetation,was established.And those indicators were further sub-classified.Based on information value model and ArcGIS's spatial analysis function,the information value of index factors was computed,and the quantitative relationship between each index factor and landslide susceptibility was examined.According to the information value of existed landslides area,the rainfall-induced landslide susceptibility was divided into 5 grades: the very low susceptibility area accounted for 10.5% of the total area;the low-susceptibility area accounted for 43.9% of the total area;the moderate susceptibility area accounted for 26% of the total area;the high susceptibility area accounted for 14.5% of the total area;the very high susceptibility area accounted for 5.1% of the total area.In terms of test of evaluation,ROC curve was used as a method for checking the accuracy of the susceptibility evaluation.And the AUC=0.770 shown that information value model of susceptibility evaluation has certain accuracy for predicting the potential landslide area.(2)Setting up the theory model of rainfall-induced landslide dynamic hazard evaluation based on mechanical-hydrological coupling model.Combining rainfall infiltration theory,water transport mechanism,shallow rainfall-induced landslide instability mechanism and study of regional stability evaluation,a full quantitative analysis theory for dynamic hazard evaluation model of shallow rainfall-induced landslide was established,which was based on mechanical-hydrological equation.The dynamic hazard evaluation model consisted of three parts: the representation of digital terrain,the hydrological condition during rainfall and the calculation of the soil column stability.Digital terrain model took the raster cell as the basic unit for computation,including altitude,slope angle and slope direction of soil column unit.Based on the improved slope Green-Ampt model,this hydrological model fully considered the lateral movement of water in the upper saturated zone and its effect on the wetting front movement.Based on limit equilibrium method soil column stability was analyzed,with the slide surface on the wetting front.Based on the physical equation,the dynamic hazard evaluation model was used to analyze the temporal and spatial variation of the slope stability during rainfall.(3)Programming the dynamic hazard evaluation model of rainfall-induced landslides,and parameter sensitivity of the model was examined and compared with the slope Green-Ampt model.Based on the theory model of dynamic hazard evaluation,Matlab programming was used to the model development.This model had total 16 parameters from 4 aspects,including controlling parameters,terrain parameters,soil parameters and rainfall parameters.For the same slope angle,the stability of the three kind of soils from high to low was followed by secondary loess,primary loess and diluvium loess.For the same soil,the larger slope angle had the shallower wetting front,but the stability coefficient was smaller,with higher hazard.The comparison with the slope Green-Ampt model shown that there was little difference in calculating wetting front depth during rainfall.But the stability calculation shown great difference between the two models.The slope Green-Ampt model was more conservative due to failure considering latter seepage in the saturated zone.(4)The rainfall-induced landslide dynamic hazard evaluation was performed through a case study of Gucheng town.The dynamic risk evaluation model was applied to calculate the shallow soil stability in Gucheng town,Qin'an County,under the 24 h and 10mm/h intensity rainfall,and obtain the hourly regional stability distribution.Based on calculated safety factor,and the hazard level of this area was divided into 5 grades.With the continuous rainfall,the factor of safety in this area gradually decreased,the hazard area increased gradually.Under the rainfall intensity of 10mm/h,when there was more than 7 hours of continuous rainfall,landslides may occur.And when there was more than 14 hours of continuous rainfall,landslides were likely to happen.When rainfall was completed(24h),the high hazard zone and very high hazard area accounted for 5.9%,and the very low hazard area(safety zone)decreased by 71.5%. |
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