Safety assessment of a gravity dam using a hydromechanical model: fracture propagation at the dam/foundation interface

Abstract

Most gravity dam failures occur due to sliding along the dam/foundation interface, rock mass discontinuities, or rock mass layers of lower strength. The possibility of sliding of a dam is usually evaluated based on simplified limit equilibrium techniques. In this study an explicit time-stepping small displacement algorithm, Parmac2D-Fflow, is used to assess the safety of gravity dams. This algorithm is based on a discrete representation of discontinuities, simulates the hydro-mechanical interaction, and considers softening constitutive laws that are closer to the actual behaviour of the dam/foundation interface. Seepage flow along the dam/foundation interface is only allowed to occur after contact failure, making it possible to model a coupled propagation failure along the dam/foundation interface due to a hypothetical dam overtopping scenario. For two gravity dams with different heights, the numerical results predicted with a coupled/fracture propagation model are compared with those obtained with a coupled/fully fractured model and with an uncoupled analysis. The results presented highlight the relevance of taking into account a coupled hydro-mechanical for dam safety and show that with coupled-fracture propagation model slightly higher safety factors are predicted.