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Abstract

Large-scale hydraulic model tests were carried out by the Leibniz University of Hannover, Germany to investigate the performance of wide-graded grain materials (0.1-200 mm) as scour protection system tested under spectral wave loads. The model tests were conducted in the Large Wave Flume (GWK) of the Forschungszentrum Küste (FZK) assuming a length scale of 1:4. The experimental setup consisted of a single layer material bed protecting a monopile (D = 1 m) as often used as offshore supporting structure. In order to measure the structure-induced scour development around the monopile acoustic backscatter systems (ABS), single-beam echosounder, and a 3D laser scanner were used. Matching environmental conditions of the North Sea, the model tests were carried out with spectral wave load (JONSWAP-spectra) and successively increasing significant wave heights up to Hs = 1.3 m. As result, a maximum scour depth of S/D = 0.161 was found after 9000 waves which resembled a synthetic storm duration of 20 h. The results indicate high stability against spectral wave load and demonstrate the capability of wide-graded material to perform reasonably well under wave loads, particularly applied in a dynamic design of scour protection.

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