| The strong damage of 5.12 Wenchuan Earthquake produced considerable secondary geological disasters, such as collapse, landslide and debris flow, under the complicated geological background conditions. It has formed a huge of loose accumulation, gestated rich source conditions for the debris flow in this area. Under the action of the heavy rainfall, debris flow happened frequently. Due to the lack of systematic research on the debris generated by earthquake, especially for its harm degree and destruction dynamics. In addition, during the process of reconstruction, because inadequate protective and unconsciousness after the earthquake, in a long time of reconstruction, debris flow disaster become the highest frequency, most destructive and widest range influence disaster. On August 14th 2010, super flash flood debris caused the devastating damage to the provincial highway 303 along Yingxiu-Genda. Therefore, within a further understanding of debris flow hazards for highway engineering evaluation, planning and provides some prevention and reduction of geological basis, could be a very good theoretical and practical significance or reference for the study of forming condition, activity, characteristics and formation mechanism of this post-earthquake debris flow.The main Understanding of this paper are as follow:(1) There are 30 debris flow sites along the highway of Yingxiu-Genda (before or after the 8.14 heavy rainfall, 15 gully debris and 15 slope debris were break out). The development of debris flow was controlled by geological conditions, the change of the formation conditions are mainly embodied in the loose material sharp increasing, geomorphology mutation or the change of permeation of the rainfall condition, most of the debris flow caused by the heavy rainfall.(2) After the Wenchuan earthquake, the formation conditions of debris flow undergone great changes. At present, the evaluation method of the predisposition of the geologic hazards which have been widely used did not highlight the main reasons of the predisposition after the disaster. So, the current methods are unreasonable. This paper, by using AHP, the original evaluation parameters have been revised, highlighted the three main factors that influenced the predisposition of the debris flow: the material sources, the critical rainfall intensity and catchment.(3) The method study of the scale of the debris flow, on the based of typical debris flow surver along the roads during the 8.14 period, compared the single biggest rushed out of the debris of one ditch with the total content source. According to the results, the maximum debris of one time could be estimated as 10% of the total content sources (material source estimate). To ensure the accuracy of the results, took the content of debris flow that have been flowed out into the Rainfall flood law formula for back calculation to correct the blockage factor in this formula. Finally, used the modified formula to calculate the single biggest rushed out of the debris of one ditch and contrast with the material source estimate, then, combined with the scale of the old debris flow for integrated forecasting. That the method of combining three more applicable in the region.(4)According to the the debris flow-prone cases the degree of the scale of predicted results and the degree of harm that may arise in the future a comprehensive evaluation, this paper assessed the risk of the debris flow. The results show that 15 of the ditches in this area are high-risk areas, 8 ditches are medium, the risk of slope debris flow are small-medium, in extreme rainstorm (year storm) cases, susceptible to or secondary occurred the debris flow hazards. Large number of debris flow area, the danger, Several suggestions could be summarized from this paper are that in the process of reconstruction the highway along Yingxiu-Genda, we should try to avoid the high-risk and destructiveness ditches, for the smaller destructive debris flow, we should take the appropriate measures to defend or management. |
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