Fuzzy Reliability Analysis Of Stability Of Karst Roof Under Pile Tip

With the large-scale development of engineering construction in our country, more and more high-rise buildings, roads, railways, bridges, airports, underground works, water conservancy and hydropower projects are build on karst area, while the harms growing caused by karst also bring more and more peoples'attention. Karst development will destroy the integrity of rocks, greatly reduce the strength and stability of the rocks. With the attached load, vibration or other complications, it may cause karst roof collapse, ground sudden settlement, foundation instability, structure damage thus causes heavy loss. And because pile foundations are sensitive to bearing capacity and deformation, it can extremely effect on pile foundations. Therefor, the stability of karst roof under pile tip is very important to the pile foundation design and construction in karst area.This paper is due to the investigation and analysis of the engineering geologic conditions, studied the influencing factors of karst roof stability and the physical and mechanical parameters of rock and soil mass, in virtue of fuzzy mathematics, rock mass strength theory and possibility theory to analyse if the stability of karst roof under pile tip is reliable. First, we found the main factors which can effect the stability of karst roof have the characters of randomicity, fuzziness and interval features, use triangular fuzzy number to define the value of parameters. In combination with plenty of geotechnical mechanical experiment data, synthetically using fuzzy mathematics theory,rock mass rating index RMR and Hoek-Brown empirical strength criterion, established a new method to calculate triangular fuzzy numbers of karst roof rock mass mechanical parameters. Second, we analysed the deformation characteristics and damage models while karst roof state in single pile load, according to the punching and shearing damage model, shearing damage model and bending damage model of karst roof, established the fuzzy limit equilibrium analysis model of karst roof under pile tip, then we get the safety factor fuzzy number for calculate the karst roof punching and shearing, shearing and bending models. Then, introducing the karst roof failure criterion, namely the roof punching and shearing, shearing and bending stability as one of which does not meet will lead the roof to instability, constructing the rational performance function, which define the probability of karst roof stability, using fuzzy reliability analysis method evaluated the reliability of pile endpoint karst roof stability. At last, in combination with the engineering practice, select a representative pile underlie karst roof, we used the fuzzy reliability method for stability analysis of karst roof under pile tip, and compared with other methods, to validate the feasibility and rationality of the proposed method.This paper, by researching the method to calculate the triangular fuzzy number of karst roof rock mass mechanical parameters, analyzes the stability reliability of karst roof under pile tip using fuzzy possibilistic reliability theory. It provides a new uncertainty method to evaluate the stability of karst roof under pile tip, has certain theoretical significance and engineering practical value.