Abstract: Debris flow is one of the main reasons to destroy highway, so debris flow danger ec=valuation is an important issue in reducing the harm of debris flow to highway. Evaluation factors of debris flow danger were retrenched based on path analysis method, and the factors which greatly influence the debris flow danger evaluation were selected, including the main channel length, the largest volume of once flow, the drainage area, the length ratio of sediment supplement, valley relative height, bending coefficient of major ditch bed and maximum rainfall in 24 h. Then extension method was applied in debris flow danger evaluation. The site of Da-Xi-Gou regional debris fully was selected for this study. Calculation were done according to the correlation functions of extension set about the four types of risk levels of the correlation, which are K₁(p) = -0.288 9, K₂(p) = 0.034 4, K₃(p) = -0.626 5, K₄(p) = -0.750 4 respectively. So the debris flow risk level of the gully is evaluated as moderate risk. The evaluation results are consistent with that of the actual survey Liu Xilin model, and the correlation method. The selection of evaluation factors is reasonable and the proposed evaluation method is feasible, which could provide a basis for mitigating debris flow disasters along highway.

Key words: engineering geology, debris flow along highway, danger evaluation, path analysis, extension method