Probability of Failure of an Embankment Dam Due to Slope Instability and Overtopping. Response to theme B

Two mechanical models of different complexity – one using Limit Equilibrium Method (Geostudio software) and the other Finite Element Method (code Cast3M) – are developed to assess the probability of failure due to slope instability considering cohesion and friction angle as random variables. Two hydraulic conditions (steady-state and transient) are also tested for both mechanical models. Fragility curves for sliding failure mode but also overtopping failure mode are then computed and combined using the Common Cause Adjustment. In order to compute the global failure probability of the dam, the resulting fragility curve representing the structural behaviour is finally combined with water pool level probabilities. The latter are calculated considering available floods data and the hydraulic behaviour of the dam-reservoir system. This paper aims to compare several cases based on different methods and assumptions to show their potential influence on the final failure probability. In this simple geometry case, the probability of failure is not affected by the mechanical model. On the other hand, the assumptions made on hydraulic conditions have a great influence on the risk of failure. The authors finally highlight that the developed finite element model is able to use random fields instead of random variables.