Researches On Partial Factors Used In Limit State Design Of Stability Against Sliding Of Gravity Dams

Gravity dam is one of the most important hadropower structures. Its stability against sliding is one of the most concerns in design. The stability includes stability against sliding along the base surface and at deep foundation. In the specification "Design Specification for Concrete Gravity Dam" (DL5108-1999), the introduction of limit state design method is a breakthrough in design theory. However, some problems still exist in the practice of the limit state design for gravity dams. How to get reasonable partial factors is an important issue in the design specification of the gravity dams. This paper presents a study on the calibration of the partial factors used in the limit state design of the stability against sliding of gravity damsFirstly, the historical development of design methods of structures is reviewed. The traditional working stress design method (WSD) has gained a great deal of experience due to its simplicity. The reliability-based design method (RBD) is based on rigorous theory and takes into account most of the uncertainties which affect the safety of the structure. The limit state design method (LSD or LRFD) is analogous to but much simpler than RBD. No significant differences exhibits between the traditional method and the limit state design method. The limit state design method included in the design specification of gravity dam (DL5108-1999) and its shortcomings are also reviewed.Based on the reliability theory, a rational framework of calibrating the partial factors is brought forward in this paper. The statistics approaches are used to evaluate the variability or uncertainty of the shear strength of rock and soil. The method of moment, linear regression method and simplified correlation method are compared. The misuse of linear regression method is dressed. Based on the rock shear strength test data, the coefficients of variation of shear strength parameters of rock are obtained by the method of moment and the linear regression method. Compared to other previous studies, the mean values and coefficients of variation of shear strength parameters are determined and used in the calibration of partial factors. At the same time, by analyzing the design value obtained by JC method, it is found that only the lognormal distribution is appropriate to describe the characteristics of the coefficients of friction and cohesion of the materials.A great number of typical cases are prepared and data of some actual projects are collected. Based on the framework established in this paper, a set of partial factors are calibrated by analyzing the cases and projects by the JC method. Finally, the partial factors are suggested.