Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical study for stability of a cross-anisotropic seabed around a harbor entrance under random waves
Lin Cui1,2 and Dong-Sheng Jeng1,2,3
1College of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China
2Qingdao Technology Innovative Center for Ocean Dynamic Environmental Simulation, Qingdao University of Technology, Qingdao, 266033, China
3
School of Engineering & Built Environment, Griffith University Gold Coast Campus, Queensland 4222, Australia

ABSTRACT

pore pressure and is accompanied by attenuation of the amplitude andphase lag in the pore pressure changes (Yamamoto et al., 1978). Thisis particularly important for small-amplitude waves and it could onlyliquefy momentarily in the seabed under wave troughs (Jeng, 2012).
The second mechanism is termed as the residual pore pressure, whichis the build-up of excess pore pressure caused by contraction of the soil
under the action of cyclic loading (Seed and Rahman, 1978; Sumer andFredsøe, 2002). In this study, we focus on the oscillatory mechanism
and the associated seabed liquefaction.

Assessment of the seabed behavior around the marine structure canbe 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 consideredregular wave, even though the anisotropic soil behavior and irregularwave impact might have great influence as reported in the literature. Inthis study, the random wave-induced soil responses in a cross-anisotropic
seabed around a harbor entrance are investigated. Results reveals thatmulti-directional random wave causes greater agitation within the harborbasin comparing to the regular wave. The effect of cross-anisotropic
soil behavior on the seabed response is significant and the conventionalmodels for the isotropic seabed overestimates the maximum liquefaction
depth.

Numerous investigations for the wave-induced seabed responses aroundbreakwaters have been carried out before, for example, Zhang et al.
(2011); Ye et al. (2015); Zhao et al. (2018). However, the aforementioned studies only considered soil behavior in an isotropic porous
seabed under the regular wave loading. Only a few studies consideredcross-anisotropic soil behavior in the literature. It has been reported
that cross-anisotropic properties of seabed foundation can significantly
impact the dynamic soil responses (Gatmiri, 1992; Jeng, 1997a; Zhou
et al., 2014). However, these studies have been limited to linear wave
loading.

KEY WORDS: RANS; Biot’s consolidation equations;

Crossanisotropy; Harbor entrance; Random wave; JONSWAP; Liquefaction;

INTRODUCTION

Ocean waves on an open sea area are much more than just regular waves.
There are only rare cases where waves are regarded as regular waves,for example, a swell generated by a far-field storm. Most of the time
wave profiles are considered irregular due to the influence of winds overthe sea surface and obstacles presented in the ocean. Some researches ofthe seabed responses to random wave are available. Zhou et al. (2018)studied random wave-induced seabed response based on finite element
method, while the seabed is treated as two-dimensional isotropic soil.
Celli et al. (2020) investigate the momentary liquefaction potential in
the vicinity of breakwaters with submerged berms under random wave
loading. They also considered the seabed as cross-anisotropic, but theirmodel is two-dimensional which the 3D effects like diffraction aroundthe harbor entrance or within the basin of harbor can not be obtained.

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 anddischarge cargo. It is of great importance to assess the seabed behavioraround the harbor entrances when designing the foundation of thestructures. 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 porepressure overcomes the initial effective stress between soil particles. Theoccurrence 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, twomechanisms of the wave-induced soil response have been reported in theliterature (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

The present numerical model is extended from the previous OpenFOAM
model (Liang and Jeng, 2021; Cui et al., 2022). Comprehensivevalidation tests have been performed for the numerical model, the results
are not present in this paper but can refer to Liang and Jeng (2021) and1560