The Risk Assessment Of Debris Flow In The Song-pan Section Of Chengdu-lanzhou Railway

Chengdu-Lanzhou railway from Chengdu in Sichuan province, extending to the northward to connect the proposed Lanzhou-Chongqing railway station Hadapu in Gansu province, is one of the most important main railway lines which are the connection between the southwest China and the northwest China. The Song-pan section of Chengdu-Lanzhou Railway is located in Aba state of Sichuan province,distributed along the Min-Jiang river, located in the transition zone between the western Sichuan plateau and the Sichuan basin possesses,very complex the geological environmental conditions very complex. The debris flow is developing at many points along the railway, which are serious threat to railway construction and future operation in this section. In this paper, combined with the location design of Song-pan section of Chengdu-Lanzhou railway and the field data investigated, for the12 debris flow basins in this segment which pose direct threat to the railway engineering, mathematical model theories, GIS technology, numerical simulation, etc are applied to the further study of the debris flow risk assessment of railway engineering,to establish systematic method of railway debris flow risk assessment.By analyzing the image data, the topography and geological data, the rainfall data and field investigation data of the research area, and referencing the former research of debris flow risk assessment, 10 factors are selected as debris flow hazard assessment indexs. Based on above indexs, debris flows along the railway are assigned and the obtained data is standardized and normalized. Then, by using the entropy weight method, the debris flow risk assessment index weight is determined.And debris flow hazard assessment model is set up. On the basis of the model and debris flow hazard classification standards, hazard map were established in the study area.Given the Songpan section of Chengdu-Lanzhou railway is currently under construction stage, it is hard to evaluate economic, population and social effect after suffering the debris flow disasters, for vulnerability assessment on railway engineering facilities. So in this paper, it is the ease or complexity of the engineering facilities damaged struck by debris flow that is regarded as the railway engineering facilities vulnerability assessment. From the location factors of railway engineering,engineering construction specifications and structure factors and characteristics of debris flow disasters, the article selected 8 factors as the railway engineering vulnerability evaluation indexes. Then, based on the AHP, each evaluation index weight value is calculated. Combined with the Set Pair Analysis(SPA) theory, the values of railway engineering facilities vulnerability in the debris flow section are obtained. On the basis of railway engineering facilities vulnerability classification standard, railway engineering vulnerability corresponding 5 debris flow is low vulnerability, the other 7 gully railway engineering facilities vulnerability is moderate.According to the conclusion of debris flow hazard assessment and railway engineering facilities vulnerability assessment, based on the expression of debris flow disaster risk,“R=H*V”, the risk assessment of debris flow along the railway can been obtained and risk map is established.The Donglong gully debris flow is selected as the typical gully to conduct the risk assessment. On the base of FLO-2D model, the numerical simulation of Donglong gully debris flows were carried out under different rainfall frequency(once every 50 years and once every 100 years), which can get the distributed situation of the velocity and depth of Donglong debris flow. It is the product the velocity and flow depth that is used for the debris flow intensity factor to carry out debris flow intensity zoning. On the basis of intensity zoning and rainfall frequency, Donglong gully debris flow hazard map were established. Referring to debris flow building vulnerability function and curves which Jakob, etc developed, the building vulnerability zoning of Donglong debris flow fan is established, and the railway engineering and the Zhenjiang guan station locate in the low vulnerability zone. Overlaying the vulnerability map onto the hazard map, the risk map of Donglong gully debris flow fan is formed. In the risk map, the most of railway and the station threated by Donglong debris flow locate in the low risk zone, there only a small section railway locates in the moderate risk zone.