Instability Reliability Analysis Of Gravity Foundation

The stability analysis of dam foundation had been the primary issue of dam section design. In general, the safety factor method and partial coefficient of rigid limit equilibrium theory were usually used to evaluate the foundation stability on certainty analysis in engineering circles. This method was simple operation, but its results were modified through given experience, not considering the uncertainty of instability factor. Based on the theory of structure reliability, this paper calculated the reliability of the stability against sliding of the gravity dam foundation, deep double and couple slip surfaces, while fuzzy-randomness of variates and fuzzy failure criterion were considered respectively. The research contents were as follows:First, reliability of stability against sliding of gravity dam foundation was calculated based on geometry optimization algorithm. This algorithm, according to the geometry significance of reliability index ?, converted the solution of reliability index ? to the optimization of minimum problem solved by using the Matlab's optimization toolbox, avoiding the orthogonal transformation about correlation variables and the partial derivatives of performence function. It had advantages of wide application, high efficiency. Comparative analysis of calculation results were conducted by example, considering different correlation coefficient, variability, distribution modals, and truncated distribution of three random variables including shear friction coefficient f,cohesive c, and water level hu.Second, for gravity dam deep stability reliability analysis, this paper proposed a reliability method including first and second order differences, which combined numerical difference into second-order second-moment method. Due to selecting difference Calculation instead of derivation at the iteration point of the performance function, this algorithm could solve the problem of implicit performance function which could't be calculated by the classic quadratic second ordered moment method. When function was complex with many independent variables, it was efficient compared with response surface method. Combined with a concrete gravity dam, this paper analyzed the impact on reliability of the negative correlation, distribution type and variability of the shear strength parameters of anti-slip surface,f and c.Then, this paper established fuzzy mathematical model of multi-slide surface deep stability against sliding analysis of dam, on the basis of equal safety coefficient method. It considered the fuzziness of parameters and limits of the state, and presented the corresponding solution method. When this method processed the ambiguity of parameters, it was converted into the equivalent random variables, according to the variable membership function forms. It was represented by a level cut set of fuzzy constraint when dealing with the fuzziness of structural limit state. Thus, the classic method of reliability theory could be applied to analyse the fuzzy random reliability. Combined with an engineering instance, this paper explored the influence of a level cut set and the forms of membership function on calculation results.Finally, this paper summarized some useful research results, which provided important indicators and research ideas for safety assessment and decision-making of concrete gravity dam.