Considerations for Stability Analysis of Concrete Gravity Dams

Evaluating the potential for sliding or related global failure modes is a fundamental part of assessing the stability of existing and new concrete gravity dams. Limit equilibrium methods are commonly used for stability assessments of new and existing gravity dams and are also commonly utilized in engineering guidelines to define design criteria for gravity dam stability. Although dam engineers are familiar with the limitations of limit equilibrium methods and the options for alternative analysis methods, there is less experience with using alternative methods, particularly evaluating and comparing results with limit equilibrium results.
This paper describes some limitations of using limit equilibrium methods to evaluate the global stability of concrete gravity dams and presents an application of continuum based numerical methods to assess failure modes associated with weak layers in the sedimentary rock foundation of a dam. The example illustrates how the two methods can be used in complementary fashion to gain enhanced insight into the stability of a concrete gravity dam.
The differences between total and reactive stress approaches to determine effective stresses in limit equilibrium analysis of a concrete dam section are discussed. Watermeyer’s (2006) conclusion that the reactive stress approach is erroneous is also explained. Differences in engineering guidance from several government agencies for performing limit equilibrium analysis and evaluating results are discussed. The limitations of limit equilibrium analysis for modeling failure modes associated with weak near horizontal layers in a sedimentary rock foundation are illustrated with an example problem.