Abstract：The values of factors that affect the stability of karst roof under pile tip in karst area have the characters of randomicity，fuzziness and interval features. So，triangular fuzzy numbers are firstly used to express the calculating parameter value¢s distributions of possibility. They can reflect the uncertainty when determining the parameters. Based on these fuzzy numbers，the fuzzy limit equilibrium analysis model of karst roof under pile tip is presented，which can consider the action of punching and shearing，shearing and bending effects at the same time. For analysis，the method to determine triangular fuzzy numbers is proposed by comprehensive application of fuzzy mathematics theory，rock mass rating index RMR and Hoek-Brown empirical strength criterion. And level- sets technique and interval number algorithm are introduced to calculate the corresponding fuzzy numbers of the safety factor with the triangular fuzzy numbers and fuzzy limit equilibrium analysis model. Then，the performance function is suggested to evaluate the stability of karst roof under pile tip. The fuzzy possibilistic reliability analysis method for stability of karst roof under pile tip is finally put forward. This method is proven to be rational and feasible by case study，and it provides a new uncertainty analysis method for stability evaluation of karst roof under pile tip.
