Breaching in sand embankments: Flow-soil interaction

The breaching of an earthen embankment is a complex process including several parameters. Regarding this complexity, this breaching process is often modelled in a simplified way, assuming a given empirical evolution of the breach. In the particular case of breaching due to overtopping - the most frequent failure mode for embankments - the breaching process can be simulated using detailed physical models. These models are based on the physical modelling of hydrodynamics, sediment transport and geotechnical stability. This paper presents a physically-based numerical model to simulate the formation of a breach in a non-cohesive sand embankment The numerical model is based on the two-dimensional Saint-Venant - Exner equations, coupled to an empirical equation for sediment transport. The Saint-Venant - Exner equations are solved using a first-order finite volume scheme, with a HLLC solver for the flux computation. This study focuses especially on the sediment transport, by comparing various empirical formulations for bed-load sediment transport. A slope failure operator is also coupled to the model to simulate the breach widening, due to the successive failures of sand blocks. The numerical model is then applied to an experimental simplified-test case. This test analyses the breaching process in a small-scale embankment made of homogenous sand. A comparison between numerical results and experimental measurements highlights the ability of the numerical model in simulating the global breaching process: both the deepening and the widening of the breach are successfully modeled. The results are nevertheless sensitive to the empirical sediment transport formulation, with simulated peak outflow varying up to 50% depending on the choice of the formula. © Société Hydrotechnique de France, 2015