中文摘要：

为了使隧道洞口施工风险得到有效控制,建立了马峦山隧道洞口失稳的故障树,利用三角模糊数理论,确定了洞口失稳底事件的概率和重要度。同时引入模糊成本重要度的概念,结合提出的风险等级表,对马峦山隧道洞口失稳风险进行了评估。评估结果表明：洞口施工的总体风险等级为＂Ⅱ级中度风险＂;在10个风险事件中,3个为＂Ⅱ级中度风险＂,7个为＂Ⅰ级,低度风险＂。

英文摘要：

This paper established the fault tree for portal instability of Maluan mountain tunnel,using triangular fuzzy number theory,which figured out the probability and the importance degree of those selected key events of the hole collapses for controlling the risk of tunnel portal construction effectively. In addition,it introduced a concept of fuzzy cost importance that evaluated the Maluan mountain tunnel instability,combined with the risk rating table. Shown as the evaluation results： the overall risk level for the construction of the portal is＂level Ⅱ,moderate risk＂; in those selected ten key events,three of them are evaluated for ＂level Ⅱ,moderate risk＂and seven of them are＂levelⅠ,low risk＂.