The Research Of Numerical Simulation On The Initiation And Run-out Scale Of Post-earthquake Debris Flow Based On OpenLISEM

Landslides,collapses and unstable slopes caused by the Wenchuan earthquake on May 12,2008 are prone to deform under the condition of rainstorm,resulting in a debris flow.The study area is located in Longxi river basin of Longchi town in the northwest of Dujiangyan city,which was seriously affected by the " 5.12" Wenchuan earthquake,and there were a lot of loose materials caused by earthquake landslide in the basin,providing a rich source of material for the outburst of debris flow.On August 13,2010,a heavy rainstorm hit Longxi River,triggering massive debris flow,which caused the height of the Longxi river bed to rise by nearly 5m,burying houses and roads.Meanwhile,in this basin,Bayi gully,Shuida gully,Huangyang gully,Maliu gully and other debris flow gullies had different degrees of river blocking,which brought serious difficulties for post-disaster reconstruction,causing huge economic losses.Due to the complex geological conditions in the area,the use of the existing debris flow out-of-range prediction model to assess the debris flow in the strong earthquake region will appear larger errors.Considering that the accumulation area is the main area where the debris flow disasters occur,it is of great practical significance to study the numerical simulation method of debris flow accumulation and quantitatively analyze the occurrence process and result of debris flow disaster.After the Wenchuan earthquake,the secondary geological disasters in the earthquake-stricken areas were very active,especially the frequent outbursts of debris flows,large-scale and long-term impact periods,which are mainly related to the large number of sources generated by the earthquake.With the vegetation restoration,the depletion of the source and the decrease of the loose solid material reserves,the activity of the debris flow will attenuate.Therefore,the effective determination of the possible dangerous range of debris flow has important reference value for the formulation of disaster prevention and mitigation planning.In the study area,the mass rainstorm debris flow triggered by the “8.13” rainstorm around the Longchi town in the Wenchuan strong earthquake area is selected as the research sample.In addition to the relative elevation difference and catchment area,the outflow range of debris flow is also closely related to factors such as channel curvature,microtopography,rainfall and the density of debris flow.Through field investigations of “8.13” debris flow disasters,interpretation of geological hazards by using high-resolution remote sensing image,and combining Arcgis to assign attribute information to the interpretation results,a source-source attribute database for the study area was established;Through the investigation of vegetation restoration in the field study area and the analysis of related research data,the land use types and related databases in the study area were obtained,including vegetation height distribution,vegetation coverage rate,leaf area index,etc;Through field infiltration test and indoor test,physical and mechanical properties of debris flow source were obtained,including permeability coefficient,initial moisture content,internal friction angle,porosity,internal cohesion,average particle size,boundary particle size d50 and d90,etc;using the topographic factors of debris flow in the study area obtained by 1: 50000 topographic data,and combining the spatial analysis technology of Arc GIS,the terrain gradient,flow rate and flow direction of the study area are obtained.This paper discusses the formation mechanism and accumulation characteristics of debris flow in the study area,and analyzes the influence of continuous rainfall,source recharge and topographic features on the debris flow activity;and the depth and extent of the debris flow in the study area were obtained by using the Open LISEM model to simulate the movement and accumulation process of the debris flow.Using the actual debris flow data of the study area to verify the practicality of the forecasting simulation,the results show that the OpenLISEM model is feasible for the prediction of the actual debris flow out-range,which is helpful for the authorities to choose future relocation safety sites,and can also serve as an important basis for debris flows risk management.It can also be used for assessments in geological engineering related field and provide historical development estimates to debris flow surveys.