• Geomechanics and Engineering
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• 제6권4호
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• pp.377-389
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• 2014

The vacuum consolidation method which was proposed by Kjellman in 1952 has been studied extensively and used successfully since early 1980 throughout the world, especially in East and Southeast Asia. Despite the increased successful use, different opinions still exist, especially in connection to distribution of vacuum with depth and time in vertical drains and in soil during preloading of soft ground. Porewater pressure measurements from actual cases of field vacuum and vacuum-fill preloading as well as laboratory studies have been examined. It is concluded that (a) a vacuum magnitude equal to that in the drainage blanket remains constant with depth and time within the vertical drains, (b) as expected, vacuum does not develop at the same rate within the soil at different depths; however, under ideal conditions vacuum is expected to become constant with depth in soil after the end of primary consolidation, and (c) there exists a possibility of internal leakage in vacuum intensity at some sublayers of a soft clay and silt deposit. A case history of vacuum loading with sufficient subsurface information is analyzed using the ILLICON procedure.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1992년도 가을학술발표회 논문집
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• pp.121-130
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• 1992

Assessement of comsolidation characteristics of soft soil is very important in the project of soft soil improvement. In the design step, the consolidation characteristics of soil is determined by the laboratory tests (typically oedometer test), generally. But there is big differences between the condition of laboratory test and the condition of field(in situ). the differences results in the considerable difference between the predicted and measured consolidation behavior. This article analyzed the consolidation data of the "SOFT SOIL IMPROVEMENT PROJECT of the 2nd Namdong Industrial Complex at Inchon". The project was improving the road way net work in the 2nd Namdong Industrial Complex by preloading and sand pile method. Field instrumentation was performed at 10 points which consist of pneumatic piezometers, magnetic probe extensometers, inclinometers and electronic dipmeter. The results showed that there is big difference in the laboratory predicted consolidation behavior and field consolidadion behavior. Also there was big difference in the settlement behavior and pore pressure behavior. This article investigated the above factors by comparing the settlement, pore pressure and strength at different conditions.onditions.

• Geomechanics and Engineering
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• 제5권6호
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• pp.565-574
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• 2013

Extensive study was carried out on Clay expansive soil. This soil was silty clay and can be classified as CH. The degree of expansion was found to range from low to medium depending on the free swell and swell pressure tests. The research investigated the effect of using cement dust on swelling potential, Atterberg Limit, linear shrinkage, and mineralogical composition of expansive soil. The results showed that the swelling potential, plasticity index, linear shrinkage, and clay minerals decrease with increasing cement dust percentage. The cement dust accumulates in huge amounts as a side product in cement factories, and the disposal of this fine dust is very difficult and poses an environmental threat.

• Coupled systems mechanics
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• 제3권2호
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• pp.233-245
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• 2014

Coupled finite element analysis is carried out to study the effect of degree of saturation on the vertical displacements and pore water pressures simultaneously by developing a FORTRAN90 code. The finite element formulation adopted in the present study is based upon Biot's consolidation theory to include partially saturated soils. Numerical methods are applied to a two-dimensional plane strain strip footing (flexible) problem and the effect of variable degree of saturation on the response of excess pore water pressure dissipation and settlement of the footing is studied. The immediate settlement in the case of partly saturated soils is larger than that of a fully saturated soil, the reason being the presence of pore air in partially saturated soils. On the other hand, the excess pore water pressure for partially saturated soil are smaller than those for fully saturated soil.

• Journal of applied mathematics & informatics
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• 제41권2호
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• pp.295-309
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• 2023

The Richards' equation attracts the attention of several scientific researchers due to its importance in the hydrogeology field especially porous soil. This work presents a numerical method to solve the two dimensional Richards' equation. The pressure form and the mixed form of Richards' equation are solved numerically using a bivariate diamond finite volumes scheme. Euler explicit scheme is used for the time discretization. Different test cases are done to validate the accuracy and the efficiency of our numerical model and to compare the possible numerical strategies. We started with a first simple test case of Richards' pressure form where the hydraulic capacity and the hydraulic conductivity are taken constant and then a second test case where the hydrodynamics parameters are linear variables. Finally, a third test case where the soil parameters are taken according the Van Gunchten empirical model is presented.

• 한국터널지하공간학회 논문집
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• 제17권3호
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• pp.305-317
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• 2015

본 연구는 Shield TBM 굴착시 지표침하에 대한 주요 요소를 선정하기 위하여 3차원 지반해석 프로그램을 이용하여 막장압, 뒤채움압, 굴진장, 지반모델 및 요소망에 대한 다양한 조건을 적용하여 수치해석을 수행하였다. 수치해석에 의한 지표침하 산정결과 뒤채움압과 지반모델조건이 가장 큰 영향을 미치는 요소로 판단되었으며 향후 지반조건 및 장비특성에 따른 사례를 추가하여 연구를 보완하고자 한다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.295-302
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• 2000

Earthquakes not only produce additional load on the structures and underlying soil, but also change the strength characteristics of the soil. Therefore, in order to analyze soil structures for stability, the behaviour after earthquake must be considered. In this paper, a series of cyclic triaxial tests and monotonic triaxial tests were carried out to investigate the undrained shear strength and liquefaction strength characteristics of Nak-Dong River sand soils which were subjected to cyclic loading. The sample was consolidated in the first stage and then subjected to stress controlled cyclic loading with 0.1Hz. After the cyclic loading, the cyclic-induced excess pore water pressure was dissipated by opening the drainage valve and the sample was reconsolidated to the initial effective mean principal stress(p/sub c/'). After reconsolidation, the monotonic loading or cyclic loading were applied to the specimen. In the results, the undrained shear strength and liquefaction strength characteristics depended on the pore pressure ratio(Ur=U/p/sub c/'). The volume change following reconsolidation can be a function of cyclic-induced excess pore water pressure and the maximum double amplitude of axial strain.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1140-1147
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• 2005

The objective of this study was to identify the effect of the degree of saturation on the resilient modulus of cohesive soils as subgrade. Six representative cohesive soils representing A-4, A-6, and A-7-6 soil types collected from road construction sites across Ohio, were tested in the laboratory to determine their basic engineering properties. Resilient modulus tests were conducted on unsaturated cohesive soils at optimum moisture content, and samples compacted to optimum conditions but allowed to fully saturate. The subgrade compacted at optimum moisture content may be fully saturated due to seasonal change. Laboratory tests on fully saturated cohesive soils showed that the resilient modulus of saturated soils decreased to less than half that of soil specimens tested at optimum moisture content. The reduction of resilient modulus would possibly be caused by the buildup of pore water pressure. In resilient modulus testing performed in this study on saturated samples, pore water pressure increases were observed. Pore water pressure and residual pore water pressure gradually increased with an increase in deviator stress.

• Geomechanics and Engineering
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• 제5권3호
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• pp.241-261
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• 2013

The bearing mechanism of pile during installation and loading process which controls the deformation and distribution of strain and stress in the soil surrounding pile tip is complex and full of much uncertainty. It is pointed out that particle crushing occurs in significant stress concentrated region such as the area surrounding pile tip. The solution to this problem requires the understanding and modeling of the mechanical behavior of granular soil under high pressures. This study aims to investigate the sand behavior around pile tip considering the characteristics of sand crushing. The numerical analysis of model pile loading test under different surcharge pressure with constitutive model for sand crushing is presented. This constitutive model is capable of predicting the dilatancy of soil from negative to positive under low confining pressure and only negative dilatancy under high confining pressure. The predicted relationships between the normalized bearing stress and normalized displacement are agreeable with the experimental results during the entire loading process. It is estimated from numerical results that the vertical stress beneath pile tip is up to 20 MPa which is large enough to cause sand to be crushed. The predicted distribution area of volumetric strain represents that the distributed area shaped wedge for volumetric contraction is beneath pile tip and distributed area for volumetric expansion is near the pile shaft. It is demonstrated that the finite element formulation incorporating a constitutive model for sand with crushing is capable of producing reasonable results for the pile loading problem.

• 한국지반공학회논문집
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• 제30권8호
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• pp.13-24
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• 2014

지반아칭을 규명하기 위해 일련의 트랩도어 모형실험을 실시하였다. 이 모형실험에서 지반아칭현상은 모형토조바닥에 작용하는 연직토압의 변화를 관찰함으로서 확인할 수 있었다. 트랩도어 재하판의 하강으로 지반변형을 발생시킴으로서 트랩도어 상부지반에 이완영역이 발생하였다. 이때 이완영역내의 응력은 지반아칭현상에 의해 트랩도어 주변의 정지영역으로 전이됨을 알 수 있었다. 즉 연직토압은 이완영역 내에서는 급격히 감소하였고 정지영역에서는 크게 증가하였다. 이완영역 내 연직토압의 최대감소율과 정지영역에서의 연직토압의 최대증가율은 지반밀도에는 영향을 받지 않았으나 트랩도어 재하폭의 크기에는 영향을 크게 받았다. 이완영역은 타원형상으로 정의할 수 있었으며 이타원의 장축은 트랩도어 중앙에서의 이완영역높이의 두 배 크기에 해당하였고 단축은 트랩도어 폭 크기에 해당하였다. 여기서 트랩도어 중앙에서의 이완영역높이는 트랩도어 폭의 1.5배 크기로 나타났다.