Seabed saturation conditions from in-situ measurements performed on Norderney

This paper deals with an important coastal engineering problem of defining proper seabed saturation conditions, which have a significant influence on the pore-fluid compressibility and the wave-induced cyclic response of poro-elastic seabed sediments. A unique in-situ measuring campaign was conducted in the tidal zone of the northern beach of Norderney, off the North Sea coast of Germany, where 186 sandy seabed samples were taken underwater. Based on the laboratory measurements, a set of calculated saturation degrees was statistically analysed. Both the histogram and the normal Q-Q plot, as well as the Shapiro-Wilk normality test, confirmed the validity of the assumption of the normal probability distribution for the variability of the degree of saturation. The mean degree of saturation of the top layer of the seabed, 𝑆 𝑟 = 0.973 , constitutes the main output of the study, whereas the uncertainty propagation analysis enabled to define the possible range of variation, which is 0.962 ≤ 𝑆 𝑟 ≤ 0.986 . It should be clearly emphasised that a proper assessment of the seabed saturation conditions is very important, mainly due to the correctness of the description of the wave-induced pore-fluid pressure field used in more detailed analyses of the pore-fluid pressure gradients and the liquefaction potential of the seabed, which have a direct impact on phenomena such as sand transport on beaches, seabed erosion, and stability of coastal structures (e.g. breakwaters and submarine buried pipelines)