Experimental Study of Scale and Model Effects for Wave Impacts on Dike Mounted Vertical Walls
2Faculty of Civil Engineering and Geosciences, TU Delft, The Netherlands
3Engineering Research Center, Deparmtment of Civil and Environmental Engineering, Colorado State University, USA
4Flanders Hydraulics Research, Flanders Hydraulics Research, Belgium
5Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Firenze, Italy
Introduction: Coast protections of low lying countries, such as The Netherlands, Belgium, UK and Germany are often comprised of a mild foreshore and shallow waters, followed by a sloping structure (e.g. a dike) and a promenade. In this setting, waves can overtop the dike and impact on the storm wall or building on the dike. Design guidance for the impact force on dike mounted vertical structures is often derived from small-scale laboratory experiments. Hence, a study on scale effects of overtopped wave impacts is required to estimate the error when upscaling the small-scale results to prototype.
Experimental set-up: Large-scale experiments were carried out in the WALOWA project. A scale model geometry was constructed in the Delta Flume (The Netherlands). It was comprised of a (1) a sandy foreshore with a slope of 1/35 over a flume length of 80m, (2) a concrete dike with a 1/2 slope, (3) a 2.3m wide promenade, and (4) a vertical, 1.6m high wall at the end of the promenade. Irregular waves representing a storm with a 1000 and 17000 years return period were generated. The wave parameters along the flume and the wave impact pressures and forces on the wall were measured. Small-scale experiments, conducted on a similar geometry and using the same series of waves were obtained from wave flume experiments at Ghent University.
Preliminary results: To ensure comparability between large- and small-scale model the wave parameters were studied first. The time-series of waves at the offshore location coincided well (Hm0,o difference = 1.1%) between the data-sets and deteriorated more (Hm0,t difference = 3.6%) at the toe of the dike. Secondly, the impact forces were compared based on the time-series of individual impacts, Fmax and averaged parameters such as F1/250, F10%. Furthermore, model effects and repeatability of tests will be investigated. Eventually the error due to scale and model effects for overtopped wave impact measurements in laboratory experiments will be estimated.
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