Assessment of the seabed behavior around the marine structure can be a critical process in designing its foundation because of numerous structure failures due to seabed instability. Most of previous studies were either based on the assumption of soil isotropy or only considered regular wave, even though the anisotropic soil behavior and irregular wave impact might have great influence as reported in the literature. In this study, the random wave-induced soil responses in a cross-anisotropic seabed around a harbor entrance are investigated. Results reveals that multi-directional random wave causes greater agitation within the harbor basin comparing to the regular wave. The effect of cross-anisotropic soil behavior on the seabed response is significant and the conventional models for the isotropic seabed overestimates the maximum liquefaction depth.
Breakwaters are usually built surrounding a harbor to sufficiently shelter vessels from the wave impact, as well as providing a channel entrance for the navigation through the port and a tranquil place to load and discharge cargo. It is of great importance to assess the seabed behavior around the harbor entrances when designing the foundation of the structures. This is because many examples of breakwater failures due to seabed instability have been report in the literature (Puzrin et al., 2010; del Campo and Negro, 2011). One of the well-known failure mechanisms is soil liquefaction, which occurs when the excess pore pressure overcomes the initial effective stress between soil particles. The occurrence of soil liquefaction can be fatal to the structure stability as the soil acts like fluid and loses its bearing capacity.
Based on the observations in the laboratory and field measurements, two mechanisms of the wave-induced soil response have been reported in the literature (Zen and Yamazaki, 1990; Jeng, 1997b; Sumer and Fredsøe, 2002) depending on the manner that the pore pressure is generated. The first mechanism resulted from the transient or oscillatory excess pore pressure and is accompanied by attenuation of the amplitude and phase lag in the pore pressure changes (Yamamoto et al., 1978). This is particularly important for small-amplitude waves and it could only liquefy momentarily in the seabed under wave troughs (Jeng, 2012). The second mechanism is termed as the residual pore pressure, which is the build-up of excess pore pressure caused by contraction of the soil under the action of cyclic loading (Seed and Rahman, 1978; Sumer and Fredsøe, 2002). In this study, we focus on the oscillatory mechanism and the associated seabed liquefaction.