Experimental investigation of the erosion of a sand dike by overtopping

Van Emelen, Sylvie [UCL] Ferbus, Vincent [UCL] Spitaels, Thibaut [UCL] Zech, Yves [UCL] Soares Frazao, Sandra [UCL]

A good knowledge of erosion processes during dike breaching is essential to evaluate the extent of the flood. So this paper presents the results of a new series of laboratory experiments on erosion of an overtopped non-cohesive sand dike. The setup represents a 2D-V problem with a narrow slide of dike between two glass walls. Two different uniform sediment grain sizes were tested: coarse sand (d50 = 1.85 mm) and fine sand (d50 = 0.61 mm). The focus is first set on the seepage effect into the dike failure process. For the coarse sand, characterized by an important permeability, the seepage is too important to study a failure governed by pure overtopping. On the contrary, with the fine sand, the presence of a sand layer downstream of the dike, acting as a drain, avoids any sliding of the downstream toe. The second part of the study focuses on the dike erosion in presence of a downstream sand layer, ensuring failure governed by pure overtopping. Two sets were performed with distinct inflow in the upstream reservoir. The overall erosion process is comparable for both sets, with direct deposition downstream of the dike, and the formation of large antidunes during the lowering of the crest level. It is shown that the higher inflow discharge only accelerates the erosion during the first phase.