• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.143-152
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• 1998

해안구조물 설치시 기초지반의 안정성 해석을 위한 파랑에 기이한 액상화 메카니즘을 과잉간극수압(excess pore pressure) 현상과 관련하여 논의하였다. 과잉간극수압 발생 메커니즘에 있어서 두 가지 형태, 즉 변동과잉간극수압 (Oscillatory excess pore pressure) 및 잔류과잉간극수압 (Residual excess pore pressure) 각각에 기인한 액상화의 특성을 구명하였다. 또한, 과잉간극수압 및 해저지반의 액상화 가능성에 대한 평가공정을 제시하였는데 이는 모형실험과 현장관측자료에 의해 그 적용성이 검증되었다. 이러한 평가공정(Assessment Procedures)은 투수성 해저/기초 지반의 액상화를 추정하는데 이용될 수 있다. 해안구조물 기초 설계 및 해저 지반의 안정성 평가시 액상화의 가능성 또는 과잉간극수압의 적절한 평가.고려가 무엇보다 중요하다고 사료된다.

• 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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.5
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• pp.324-338
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• 2015

Analytical solutions for interaction between seabed and waves such as progressive wave or partial standing wave with arbitrary reflection ratio or standing wave have been developed by many researchers including Lee et al.(2014; 2015a; 2015b; 2015c; 2015d) and Yamamoto et al.(1978). They handled the pore-water pressure as oscillating pore-water pressure and residual pore-water pressure separately and discussed the seabed response on each pore-water pressure. However, based on field observations and laboratory experiments, the oscillating and residual pore-water pressures in the seabed do occur not separately but together at the same time. Therefore, the pore-water pressure should be investigated from a total pore-water pressure point of view. Thus, in this paper, the wave-induced seabed response including liquefaction depth was discussed among oscillating, residual, and total pore-water pressures' point of view according to the variation of wave, seabed, and flow conditions. From the results, in the field of flow with the same direction of progressive wave, the following seabed response has been identified; with increase of flow velocity, the dimensionless oscillating pore-water pressure increases, but the dimensionless residual pore-water pressure decreases, and consequently the dimensionless total pore-water pressure and the dimensionless liquefaction depth decrease.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.3
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• pp.91-100
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• 1988

Assuming that tidal level is constantly changed with an amplitude of 10 meters and a cycle of 12 hours, the slope stability for a typical dyke is analysed. The variation of pore water pressure within the dyke during the tidal change is obtained using a computer program, FLUMP, which is incorporated with saturated-unsaturated and transient flow. The results show that the variation of free water surface and distribution of pore water pressure within the dyke during the tidal fluctuations can be clearly predicted with the computer program. When a tide is lowered to the minimum level, the predicted pressure head is higher than the level of the free water surface in some parts of the dyke; that is, excess pore water pressure is generated in a zone affected by the tidal change. Also an unsaturated zone which shows negative pore water pressure is temporally created when a tide is lowered. The shear strength of the zone can be predicted based on the proposal suggested by Fredlund et al. It is emphasized that the excess pore water pressure generated during tidal fluctuations and strength parameters for the unsaturated zone should be considered in analyzing the slope stability of dykes. When those are considered, the critical slip surface seems to be located below the free water surface obtained when a tide is at the lowest.

• 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.

• Journal of the Korean Society of Groundwater Environment
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• v.7 no.2
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• pp.59-65
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• 2000

The vertical distribution of pore water pressure in the highly saturated sand layer under the oscillating water pressure is studied theoretically and experimentally. By the experiments it is shown that the water pressure acting on the sand surface propagates into the sand layer with the damping in amplitude and the lag in phase, and that the liquefaction, the state that the effective stress becomes zero, occurs under certain conditions. These experimental results are explained fairly well by the same theoretical treatment as for the ground water problems in the elastic aquifer. The main characteristics of liquefaction clarified by the analysis are as follows: 1) The depth of the liquified layer increases with the increase of the amplitude and the frequency of the oscillating water pressure. 2) The increase of the volume of the water and the air in the layer increases the liquified depth. Especially the very small amount of the air affects the liquefaction significantly. 3) The liquified depth decrease rapidly with the increase of the compressibility coefficient of the sand. 4) In the range beyond a certain value of the permeability coefficient the liquified depth decrease with the increase of the coefficient.

• Journal of the Korean Geophysical Society
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• v.4 no.3
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• pp.197-203
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• 2001

The vertical distribution of pore water pressure in the highly saturated sand layer under the oscillating water pressure (water wave) us studied theoretically and experimentally. By the experiments it is shown that the water pressure acting on the sand surface propagates into the sand layer with the damping in amplitude and the lag in phase, and that the liquefaction, the state that the effective stress become zero, occurs under certain conditions. These experimental results are explained fairly well by the same theoretical tearment as for ground water problems in the elastic aquifer. The main characteristics of liquefaction clarified by the analysis are as follows: 1) The depth of the liquified layer increases with the increase of the amplitude and the frequency of the oscillating water pressure. 2) The increase of the volume of the air in the layer increases the liquified depth. Especially the very small amount of the air affects the liquefaction significantly. 3) The liquefied depth decrese rapidly with the increase of the compressibility coefficient of the sand. 4) In the range beyond a certain value of the permeability coefficient the liquified depth decrease with the increase of the coefficient.

• The Journal of Engineering Research
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• v.4 no.1
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• pp.125-135
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• 2002

The vertical distribution of pore water pressure in the highly saturated sand layer under the oscillating water pressure (water wave) is studied theoretically and experimentally. By experiments it is shown that the water pressure acting on the sand surface propagates into the sand layer with the damping in amplitude and the lag in phase, and that the liquefaction, the state that the effective stress becomes zero, occurs under certain conditions. These experimental results are explained fairly well by the same theoretical treatment as for the ground water problems in the elastic aquifer. The main characteristics of liquefaction clarified by the analysis are as follows: 1) The depth of the liquefied layer increases with the increase of the amplitude and the frequency of the oscillating water pressure. 2) The increase of the volume of the water and the air in the layer increases the liquefied depth. Especially the very small amount of the air affects the liquefaction significantly. 3) The liquefied depth decrease rapidly with the increase of the compressibility coefficient of the sand. 4) In the range beyond a certain value of the permeability coefficient the liquefied depth decrease with the increase of the coefficient.