In the practice of engineering, breaking wave is much more dangerous for the stability of composite breakwater built on porous seabed than non-breaking wave in offshore area. In previous investigations or design codes, the empirical formulations generally were adopted to estimate the wave impact acting on the lateral side of caisson. The interaction between breaking wave, seabed foundation and composite breakwater is not taken into consideration. In this study, adopting the integrated numerical model PORO-WSSI 2D developed by (Ye, 2012a) and (Jeng et al., 2013), the interaction mechanism between breaking wave, seabed foundation and composite breakwater is investigated numerically. In PORO-WSSI 2D,the Volume-Averaged Reynolds Averaged vier-Stokes (VARANS) equations govern the wave motion and the porous flow in seabed foundation and in rubble mound; and the dymic Biot's equations (known as "u-p" approximation) govern the dymic behaviors of seabed foundation and composite breakwater under breaking wave loading. Numerical alysis indicates that the turbulent energy of breaking wave is significant, and the wave impact on caisson applied by breaking wave is much greater than non-breaking wave. The composite breakwater and its seabed foundation respond to the breaking wave loading intensively. The maximum horizontal vibration magnitude of the composite breakwater is up to 5 mm; the maximum liquefaction depth in the seabed in front of the composite breakwater reaches up to 1.2 to 1.6 m. The parametric study shows that the permeability and saturation of seabed, wave height are three domint factors for the wave-induced liquefaction in seabed foundation.
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