The Risk Assessment Of Debris Flow After The Wenchuan Earthquake Along Yingxiu-Wolong Highway Of S303Line

About80%of the YW road (Yingxiu to Wolong of the S303) has been seriouslyburied or damaged in the "5.12" earthquake. The road was reconstructed on the original.However, the reconstructed one was damaged by the debris flow around August14,2010,which leaded the Yingxiu to Gengda road scrapping. The road was reconstructed by therelevant departments through plan, design, accurate evaluation, and forecast of the debrisflow are the keys, which are the basics of conducting risk assessment of designed roadinfrastructures and giving the preventions of road safety.The debris flow and highway infrastructure of the road was research object in thispaper, which through the analysis of highway engineering geological conditions of thearea, study the development, distribution characteristics and formation mechanism ofdebris flows, evaluated debris flow danger after the earthquake. According to the debrisflow hazard danger, evaluating vulnerability of highway infrastructure vulnerability hasimportant practical significance for the highway planning design and reconstruction.Risk analysis method was used which analysis the disaster factors, the bearing body, thepossibility and its damage of the debris flows, and then build the highway debris flowrisk assessment system, which has theory significance for debris flow study afterearthquake and highway debris flow risk assessment. This paper made some results inthis aspect.(1) There are a total of28development debris flow gullies along the road, and allof them are induced by the heavy rainfall, and its fluid property mainly watery debrisflow. There are21development debris flow gullies in Yingxiu to the seven-story channel,which occupy3/4of the total line of debris flow, and this section of debris flow aremostly high-frequency debris flow, and some of debris flow never even occurred hadbroke out after the earthquake, the characteristics of this section are development density,large-scale, destructive; there are7development seven debris flow ditch along channelsto Wolong section that belongs to the old low-frequency debris flow gullies, and it haveno debris flow broken out after the earthquake. Only part of the valley upstream of thetributary have outbreak small debris flow, but this section mudslides have an obviousfeature, both of them have old debris flow deposits, and strongly weathered.(2) The latest single debris flow hazard assessment model was used: the scale ofdebris flow and the occurrence frequency of the two main factors, and the drainage area, the length of the main ditch, watershed relative height,the cutting density and theproportion of unstable trench bed five secondary environmental factors were selected toevaluate the28debris flow ditch along the highway. Combining the remote sensingimages, selecting the increase a solid material and the degree of rock loose by theearthquake to corrected the results: there are6grooves that belong to a very high risk ofdebris flow gullies,11grooves belong to a high risk of debris flow gullies,7groovesbelong to the risk of debris flow gullies, and5grooves belong to the low risk of debrisflow gullies. In addition to the governance debris flow gully, the amended riskassessment results are consistent with expert on-site evaluation results and the outbreakof the status quo.(3) Comprehensive evaluation method was adopted in analyzing the influentialfactors of the vulnerability in this paper. Different evaluation indexes were adopted todifferent road infrastructure (roadbed, culverts, bridges, tunnel): such as the indexes forthe roadbed engineering of the distance from roadbed to debris flow accumulation areaand the roadbed elevation an so on; indexes for culvert engineering of culverts clearance,flow capacity, culvert hole size, culvert outlet plus fitness, size of culvert longitudinalslope end and so on; indexes for bridge engineering of bridge position, throughputcalculation, stability of bridge pier and basis and so on; indexes for tunnel engineeringsuch as the location and elevation of tunnel exits, the stability of the tunnel body,distance from the top to bottom and so on.(4) According to the results of planning and design lines of disaster risk of debrisflow,23valleys where the level of risk is at a very low and low level，5valleys where thesections are at moderate risk level. These results proved the risk level of overall planningand design lines is low, and the design is reasonable.