Nonlinear interaction between wave, breakwater and its loose seabed foundation: A small-scale case

In offshore environment, newly deposited quaternary loose sediments widely exist in the world. Sometimes, coastal engineers cannot avoid choosing these natural loose sediments as the foundation of marine structures. Under this situation, the interaction between ocean wave, marine structures and their loose sand foundation, and the wave-induced pore pressure built-up in loose seabed foundation are the key factors in which coastal engineers would most concern. In this study, the nonlinear interaction mechanism between ocean wave, a composite breakwater and its loose elasto-plastic sand bed foundation is investigated by utilizing a semi-coupled numerical model FSSI-CAS 2D. In the coupled numerical model FSSI-CAS 2D, VARANS equation for wave model, and dynamic Biot׳s equation for soil model are used for the governing equations. The advanced and excellent elasto-plastic constitutive model PZIII proposed by Pastor et al. (1990) is adopted to describe the nonlinear dynamic behavior of loose sand soil under cyclic wave loading. Taking the parameters of Neveda sand determined in the VELACS project funded by NSF as the property parameters for the loose sand bed, a small-scale computational case like the experimental set-up in Mostafa et al. (1999) is taken as a representative case to investigate the wave-structure-loose seabed foundation interaction mechanism. The numerical results indicate that the pore pressure in loose seabed foundation builts up significantly, and the marine structure subsides and tilts under wave loading. The loose sand bed becomes denser and denser due to soil compaction. Parametric studies show that both the wave characteristics and the soil properties can affect the built-up of residual pore pressure in loose seabed foundation.