Quantifying the erosion resistance of dikes with the overflowing simulator

Bonelli, S. and Nicaise, S. and Charrier, G. and Chaouch, N. and Byron, F. and Grémeaux, Y. (2018) Quantifying the erosion resistance of dikes with the overflowing simulator. In: Protections 2018 (3rd International Conference on Protection against Overtopping), 6-8 June 2018, Grange-over-Sands, UK.

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Abstract

It is important to quantify the soil resistance against erosion cause by to the overflow of dikes and levees. Small-scale tests are excluded, due to the lack of similarity for a free-surface flow phenomenon on stepped slopes, with non-established flow and erosion of a cohesive soil. Moreover, using hydraulic laboratory flumes does not make it possible to have a correct representation of the soil in place, in terms of layer compaction. This is why we have developed an on site overflowing device. The device was deployed as part of the DigueELITE research project on a 3.5 m (9.8 ft.) high experimental dike in channels, 60 cm wide (≈2 ft.) and 15 m long (≈50 ft.), covering the downstream slope (1.5H/1V) and the downstream platform. The procedure followed is based on ASTM-D6460 standard. The test campaigns were carried out with flow rates up to 500 l/s per linear meter (0.5 m2/s), water velocity up to 5 m/s, and a discharge depth up to 30 cm (≈12 in.) at crest. Two soil types were studied: lime-treated soil, and untreated cohesive soil. The first phase of erosion is that of the surface layer. The second phase is that of the embankment constitutive soil. The erosion shows a stair-steps pattern, due to the layers of compaction. The results obtained show that lime-treated soil has better erosion resistance than untreated soil. Compared to the untreated soil, erosion in the lower part of the slope is 3 times less in lime-treated soil, and the scour depth development process at the downstream toe is 5 to 10 times smaller. This paper presents the experimental setup, the results obtained, and the perspectives. The most important findings are that overflowing experiments are feasible on site with the proposed test set-up.

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