• Geotechnical Engineering
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• v.9 no.4
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• pp.17-26
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• 1993

The mechanism of wave -induced stresses and liquefactions in a seabed is studied theoretically and experimentally, A constitutive equation which is governing wave -induced effective stresses and porepressures in an unsaturated seabed under the hydraulically anisotropic conditions is developed. It is learned that the effective stresses and excessive porewater pressures are governed by the conditions of waves and sedimentary layers, Especially the magnitude of effective stresses and the depth of disturbed zone induced by waves is controlled by the degree of saturation of the unsaturated seabeds.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.2
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• pp.100-107
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• 1991

The purposes of this study are 1) to observe the wave-induced liquefaction in the oceanic seabed. 2) to verify the liquefaction theory proposed by the Authors. The study consists of the field observation and theoretical analysis on the wave-induced liquefaction. In the field observation. The sea bottom pressures. the fluctuating pore pressures and stresses in the seabed and the changes of the water depth were observed for two years. The liquefaction theory proposed by the Authors is verified by the comparing the calculated fluctuating pore pressures with those observed in the field.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2012.06a
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• pp.15-17
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• 2012

파, 해저지반 및 해안 해양구조물과의 관계는 해안공학뿐만 아니라 지반공학 분야에서도 중요한 이슈중의 하나이며, 파랑에 의한 해저지반 내부의 압력 및 응력의 파악은 다양한 해안 해양 구조물의 기초 설계 및 해저 연안 지반의 불안정성 검토에 있어서 중요한 과제이다. 해저 지반의 불안정에 대한 문제 중, 파랑에 의한 해저지반의 액상화는 기존의 연구를 통하여, 두개의 메커니즘이 존재한다는 것이 밝혀졌으며, 이는 각각 파랑에 의해 해저지반 내부에 발생하는 과잉간극수압의 변동 특성 및 잔류 특성에 따른 것이다. 이 연구에서는 중복파에 의해 해저지반 내부에 에 발생하는 과잉간극수압에 대하여 수치해석을 하였으며, 발생하는 과잉간극 수압 중 잔류 과잉간극수압의 발생 특성과 실험 결과를 비교 분석하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.114-117
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• 2010

에너지자원(석유, 천연가스, 전기) 이송과 정보전달(해저광케이블)을 위한 다양한 형태의 해저 매설관이 해저면에 설치되어 운영이 되고 있다. 이들 매설관은 지진 또는 해저사면의 유실과 같은 자연재해로 인해 파괴되는 일들이 빈번하게 발생되고 있다. 그 외 태풍 등에 의해 발생되는 파랑하중에 의해서도 이들 매설관이 종종 파괴되는 일이 발생되기도 한다. 태풍 등에 의한 파랑하중은 해저지반에 과다한 과잉간극수압을 발생시켜 지반 액상화를 유발 세굴을 발생시키는데 이로 인해 매설관 하부에는 과도한 인장응력이 유발되어 매설관의 파괴 문제가 야기된다. 만약 석유수송 해저매설관이 파괴되면 경제적?산업적 측면에서 직접적인 피해 이외에도 해양환경에 미치는 영향은 매우 크다고 볼 수 있다. 따라서 파랑하중에 의한 해저매설관 주변 지반의 거동 분석 및 안정성 평가에 관한 연구가 요구된다.

• Journal of Navigation and Port Research
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• v.37 no.2
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• pp.173-179
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• 2013

The interaction among wave, seabed and marine structure is an important issue in coastal engineering as well as geotechnical engineering. Understanding variations of stresses and pore water pressures generated in seabed induced by waves is important for civil engineers who have to design the foundation for various marine structures and verify the instability of seabed. In the matters on seabed instability, particularly, in the case of wave-induced liquefaction of seabed, it is turned out there are two different mechanisms through previous studies. These are caused by the transient or oscillatory nature and the residual or progressive nature of excess pore water pressure generated in seabed, respectively. In this study, it is analyzed dynamic characteristics of soils sampled in seabed around the port of Kochi, Japan, through the dynamic triaxial tests and the residual excess pore water pressure in the seabed induced by seepage force of wave. In addition, the calculated residual excess pore water pressures were compared with the field data observed in the port of Kochi.

• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.26-32
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• 2007

A series of large-scale experiments were carried out in order to examine wave-induced liquefaction in a loosely packed sandbed, its afterward high densification and liquefaction by oscillatory pore pressure. The experiments were conducted in a Large Hydro-Geo Flume that can nearly solve the problems of scale effects of the sandbed, and the 50% sieve diameter of sand was 0.2 mm. The generation of residual pore pressure and its afterward high densification which had observed by Takahashi et al. (1999) in a wave flume experiment using fine sand with the size of 0.08 mm. As a result, the relative density of the sandbed after high densification was increased up to 79% and liquefaction by oscillatory pore pressure was not observed.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.45-55
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• 1999

Wave-induced response, liquefaction and stability of unsaturated seabed are studied. The unsaturated seabed is modeled as a fluid-filled polo-elastic medium. The coupled process of fluid flow and the deformation of soil skeleton is formulated in the framework of Biot's theory. The resulting governing equations are solved using a semi-analytical method to evaluate the stresses and pore water pressure of unsaturated and multi-layered seabed. The semi-analytical method can be applied to calculate a pore pressure and the stresses of in anisotropic inhomogeneous seabed. The results indicate that the degree of saturation influences mostly on the magnitudes of a pore pressure and the stresses of unsaturated and multi-layed seabed. Based on the pore pressure and stresses in seabed, the analysis on the possibilities of liquefaction and shear failure was performed. The results show that the maximum depth of shear failure occurrence is deeper than the maximum liquefaction depth.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.27-40
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• 2014

So far, studies on the settlement of breakwater have mainly been conducted through numerical model tests focusing on an analysis or through the laboratory wave tank tests using a scaled model. There has not been a study on the settlement that is measured in an actual breakwater structure. This study analyzed the data of settlement that has been measured in an actual caisson breakwater for a long time and the characteristics and causes of wave-induced settlement in the caisson (including beneath ground), based on qualitative aspect, were examined. The analysis revealed that wave clearly has an effect on the settlement in caisson, especially in the condition of high wave such as typhoon. Caisson settlement is caused by the liquefaction of ground, which is due to the increase of excess pore pressure, the combination of oscillatory excess pore pressure and residual excess pore water pressure, and the solidification process of ground due to dissipation of the accumulated excess pore pressure. The behavior of excess pore pressure in the ground beneath the caisson is entirely governed by the behavior of the caisson. Ground that has gone through solidification is not likely to go through liquefaction in a similar or a smaller wave condition and consequently, the possibility of settlement is reduced.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.49-64
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• 2014

Seabed beneath and near the coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If the liquefaction occurs in the seabed, the structure may sink, overturn, and eventually fail. Especially, the seabed liquefaction behavior beneath a gravity-based structure under wave loading should be evaluated and considered for design purpose. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using 2-dimensional numerical wave tank. The 2-dimensional numerical wave tank was expanded to account for irregular wave fields, and to calculate the dynamic wave pressure and water particle velocity acting on the seabed and the surface boundary of the structure. The simulation results of the wave pressure and the shear stress induced by water particle velocity were used as inputs to a FLIP(Finite element analysis LIquefaction Program). Then, the FLIP evaluated the time and spatial variations in excess pore water pressure, effective stress and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the analysis, when the shear stress was considered, the liquefaction at the seabed in front of the structure was identified. Since the liquefied seabed particles have no resistance force, scour can possibly occur on the seabed. Therefore, the strength decrease of the seabed at the front of the structure due to high wave loading for the longer period of time such as a storm can increase the structural motion and consequently influence the stability of the structure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.174-183
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (II).