Risk evaluation of colluvial cutting slope based on fuzzy analytic hierarchy process and multilevel fuzzy comprehensive evaluation

The stability of a colluvial slope, which is different from a rock or soil slope, is determined by the properties of both the bedrock and the colluvium. Coupled with artificial excavation and environmental effects, the stability factors of such slopes are complicated. To rapidly and effectively evaluate the risk of a colluvial cutting slope, a risk evaluation system for this type of slope is established herein. First, an evaluation index system is established, and reasonable risk evaluation indices are selected. Second, the fuzzy analytic hierarchy process (FAHP) is applied, a fuzzy pairwise comparison matrix, that must satisfy a consistency test, is constructed, and the weight of each index is determined. Third, the risk evaluation grades are divided into 4 risk grades, and the risk evaluation criteria for each basic index are determined. Finally, the three-level fuzzy comprehensive evaluation (FCE) method is applied, the membership function for each index is constructed, the membership degree is calculated, and the risk grade of the colluvial cutting slope is determined. This risk evaluation system is used to evaluate the risks of 148 colluvial cutting slopes along the Xiaomengyang-Mohan highway in Yunnan, China. The results show that there are 24 slopes of low risk (grade I), 85 of medium risk (grade II), 22 of high risk (grade III), and 17 of very high risk (grade IV). The evaluation results obtained are in good agreement with the actual slope instability states: failure occurred in 15 out of 85 slopes of risk grade II, 13 out of 22 slopes of risk grade III, and 16 out of 17 slopes of risk grade IV. This application demonstrates that the proposed risk evaluation system for colluvial cutting slopes is universal, and stable and that the calculation results are objective.