Research On Reliability Analysis Method Of Stability Against Sliding Of Gravity Dam Foundation

In early time, the safety evaluation of stability against sliding of gravity dam foundation was done by using the traditional safety factor method, but the randomness of the basic parameters was not taken in account in the traditional safety factor method, so the calculation results get from the traditional safety factor method can not completely reflect the objective reality. In order to make the design of gravity dam more scientific and reasonable, the new Design Code regulates that the gravity dam should be designed by using the partial coefficient method which is based on reliability theory, this regulation changes the deterministic design for undeterministic design. Basis on the random reliability theory, study on stability against sliding of gravity dam foundation is done by using several kinds of reliability calculation methods in this paper, following are the main contents.Firstly, the paper systematically states the relevant theories of several kinds of reliability calculation methods. The characteristics and the potential insufficients of reliability calculation methods are theoretically analysed, the relationships between different reliability calculation methods are also get. This analysis offers the theoretical basis to study the stability against sliding of gravity dam foundation by using the reliability analysis method.Secondly, the theories of the traditional safety factor method and the partial coefficient method are presented, the safety evaluation of stability against sliding of the typical dam foundation of a reservoir is done by using the traditional safety factor method and the partial coefficient method. But inconsistent conclusions are reached, the conclusion get from the traditional safety factor method is that the dam foundation does not satisfy the requirement of stability against sliding, meanwhile, the conclusion get from the partial coefficient method is that the dam foundation satisfies the requirement of stability against sliding. Through the initial analysis of the cause of inconsistent conclusions, making the importance of the further study in this paper more clear.Finally, a detailed study on stability against sliding of the dam foundation that combined with engineering example is done by using several kinds of reliability calculation methods. Through the sensitivity analysis of all random variables, three main sensitive factors are obtained, they are the shear friction coefficient, the cohesion and the headwater level. The changes of probability distribution types of the friction coefficient and the cohesion have a great effect on Sensitive coefficients of three main sensitive factors. The reliability index of stability against sliding of gravity dam foundation is smaller without the negative correlation between the shear friction coefficient and the cohesion, the calculation results is conservative. The reliability index is smaller when the probability distribution types of the shear friction coefficient and the cohesion are both theroretical normal distribution, the changes of probability distribution types of the shear friction coefficient and the cohesion have a great effect on reliability index. The reliability index is also smaller when the shear friction coefficient, the cohesion and the headwater level without truncated distribution, the truncated distribution of the headwater level has the greatest effect on reliability index. Through the comparative study of reliability calculation methods in the engineering example, two most practical methods are obtained, they are generalized JC method and generalized mapping transformation method.The paper reaches the conclusion that the gravity dam foundation in the engineering example satisfies the requirement of stability against sliding, after analyse all the safety evalution conclusions get from various methods.