Dike erosion is a crucial issue in coastal and fluvial flood risk management. These defense structures appear vulnerable to extreme hydrological events, whose potential occurrence risk seems to be recently increased due to climate change. Their design and reinforcement is, however, a complex task, and although numerical models are very powerful nowadays, real processes cannot be accurately predicted; therefore, physical models constitute a useful tool to investigate different features under controlled conditions. This paper presents some laboratory experimental results of erosion of a sand dike produced by the impact of a dam break wave. Experiments have been conducted in the Water Engineering Laboratory at the University of Cassino and Southern Lazio, Italy, in a rectangular channel: here, the sudden opening of a gate forming the reservoir generates the wave impacting the dike, made in turn of two different, almost uniform sands. The physical evidence proves that the erosion process is strongly unsteady and significantly different from a gradual overtopping and highlights the importance of apparent cohesion for the fine sand dike. The experimental results have also been compared against the ones obtained through the numerical integration of a two-phase model, which shows the reasonable predictive capability of the temporal free surface and dike profile evolution.
The paper investigates the impact of a dam-break wave on an erodible embankment with a steep slope. Both experimental and numerical analyses were carried out. The laboratory experiments have been specifically designed and performed, varying the storage water level, the elevation and the slope of the embankment. The simulations were carried out using a recent two-phase depth-integrated model, supplemented with a geofailure operator to account for the possible occurrence of geotechnical collapses. The comparison between the numerical and experimental results indicates that the two-phase model permits to fairly reproduce the experimental free surface elevation, with or without the geofailure operator. Conversely, especially for high embankment slopes, this operator appears to be crucial for predicting the observed morphological evolution. Moreover, the results show that, due to the geotechnical collapses, water and sediment velocities may have opposite sign. While models based on equal direction of the liquid and the solid motion cannot reproduce this issue, the proposed two-phase approach easily accounts for such a peculiarity of the investigated process
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