• Journal of the Korean Geotechnical Society
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• v.17 no.2
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• pp.123-134
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• 2001

본 연구에서는 화강풍화토 지반상 unpropped diaphragm wall의 거동을 연구하기 위하여 벽체의 근입깊이와 지하수위 조건을 변화시키면서 원심모형실험을 수행하였다. 원심모형실험시 diaphragm wall은 두께 8mm인 알루미늄합금을 사용하였으며, 지반굴착을 재현하기 위하여 zinc chloride 기법을 이용하였다. 수치해석은 대부분의 지반공학문제에 적용할 수 있는 SAGE CRISP 프로그램을 이용하였다. 수치해석에서 모형지반은 수정 Cam-Clay 모델, diaphragm wall은 탄성모델, 지반과 diaphragm wall 사이의 경계면요소는 슬립모델을 사용하여 2차원 평면변형률 조건으로 해석을 수행하였다. 모형실험 결과 파괴면의 직선적인 형태로 파괴면내의 배면측 지반은 벽체를 향하여 하향의 변위를 일으키면서 벽체의 회전에 의해 파괴되었다. 실험 및 유한요소해석 결과 지반의 최대침하량과 최대침하량이 발생하는 위치는 잘 일치하였으며, 깊이에 따른 벽체변위는 선형적인 관계를 나타내었다. 또한, 최대 휨모멘트와 근입깊이로 정규화한 최대 휨모멘트 발생위치($h_{Mmax}$/d=0.4)는 잘 일치하였다.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.133-144
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• 2003

Horizontal consolidation characteristics of Busan marine clay were investigated by computing coefficient of horizontal consolidation from Piezocone data and comparing their results with those of standard consolidation test. It is well known that current prediction models of $c_h$ for high plastic soils have large uncertainties, and show a great difference between the predicted and the measured values. However, the spherical models and expanding cavity theory of Torstensson(1977), and Burns & Mayne(1998) based on modified Cam-Clay model with critical limit state concepts have relative reliability in estimating $c_h$ and good applicability in highly plasticity soils. In this paper, a normalization technique was used to evaluate $c_h$ using the Burns and Mayne's method based on the dissipation test, and their normalized consolidation curves give 0.015 of time factor($T_{50}$) when 50% degree of consolidation is completed. Comparison study using Piezocone data obtained at other similar ground site shows 1.5 times less systematicality than that of standard consolidation test, which indicates considerable approximation with the measured values because standard consolidation test gives the difference of three to few times compared with the measured values. In addition, design chart for estimating $c_h$ based on the chart from Robertson et al.(1992) and using the other method of the direct prediction from the of dissipation test was newly proposed. It is judged that new proposed chart is very applicable to Korean marine soils, especially in very high plastic soils.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.179-186
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• 2005

Each static and cyclic load test was performed in a laboratory model test. As a result, ground displacement decreased and bearing capacity of the soil increased owing to the sheer strength of geosynthetics in general. In addition, numerical analysis was operated using Mohr-Coulomb, Modified Cam-Clay models, and FLAC 4.0 2D and compared with the laboratory model test. The results were shown to be of a great difference because the existing equations had not considered the characteristics that sheer strength increases with a load increment. Therefore, this paper proposes an equation of cable elements considering an effect of load given through repeated tests.

• Journal of the Korea Institute of Building Construction
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• v.1 no.1
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• pp.160-168
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• 2001

This study aims at the development of computer program for the deformation analysis of soft ground, and using this computer program, study the constraint effect of deformation heaving, lateral displacement of the soft ground reinforced with improvement of soft ground up to hard strata, under intact state(natural). The following results are obtained. 1. Improvement of soft ground to the hard strata works well against the settlement of neighboring ground. 2. the larger the rigidity or width of improvement of layer to hard strata is, the less settlement occurs. 3. Improvement of soft ground to the hard strata is of no use.

• Journal of the Korean Geotechnical Society
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• v.17 no.3
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• pp.103-110
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• 2001

관입체 주변에서 발생하는 지반의 과잉간극수압은 그 측정위치에 따라 영향을 받는 것으로 알려져 있다. 특히 관입체의 선단과 축표면에서의 간극수압반응은 상당히 다른 것으로 알려져 있다. 본 연구에서는 지반에 대한 관입시험시 주변지반에서 발생하는 간극수압의 반응에 대하여 Louisiana State University의 시험토조를 사용하여 조사하였다. 또한 시험결과를 비등방성 수정 Cam Clay 모델을 이용한 유한요소해석과 비교하였다. 본 연구로부터 관입체 주위에서 발생하는 간극수압은 예측한 바와 같이 선단부위에서 크게 나타나고, 뒤로 갈수록 작아지는 현상을 나타내었다. 이와 같은 현상은 전단에 의하여 발생한 간극수압과 압축에 의하여 발생한 간극수압의 상호간섭에 의한 것으로 나타났다.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.711-719
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• 2006

A series of geotechnical centrifuge model tests and numerical modelling have been performed to study engineering characteristics of the composite ground reinforced by both the Sand Compaction Piles(SCPs) and the deformation-reducing sheet piles. The research has covered several key issues such as the load-settlement relation, the stress concentration ratio and the final water content of the ground Totally three centrifuge tests have been conducted by changing configuration of the sheet piles, i.e., a test without the sheet pile, a test with the sheet pile at a single side and a test with the sheet piles at the both sides. In the model tests, a vertical load was applied in-flight on the ground surface. On the other hand, class-C type numerical modelling has been performed by using the SAGE-CRISP to compare the centrifuge test results using an elasto-plastic model for SCPs and the Modified Cam Clay model for the soft clay. It has been found that the sheet piles can restraint failure of foundation, thereby increasing yield stress of the ground. The stress concentration ratio was in the range of $2{\sim}4$. In addition, numerical analysis results showed reductions both in the ground heave($20{\sim}30%$) and in the horizontal movement($28{\sim}43%$), demonstrating the deformation-reducing effect of the sheet piles.

• Geotechnical Engineering
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• v.12 no.5
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• pp.17-26
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• 1996

The undrained behavior of Asan marine soil was investigated by using an automated triaxial testing device. The stress-strain behavior at the preand postfailure state of marine soil under undrained compression and eatension conditions was compared with the behavior of pure silt, pure clay and the overall behavior of Asan marine soil was predicted with the modified Camflay model and the bounding surface model. The marine soil sampled in Asan bay area was clayey silts with 70oA silt-30% clay content and the testing samples were prepared in both undisturbed and remolded conditions. All samples are normally consolidated with 400 kPa of effective mean confining pressure and each sample is unloaded to 200, 100, 67 kPa, respectively. And then the shear test was performed with different confining pressure. According to experimental results, there exists an unique failure line whose slope is lower than silt's and higher than clay's. It is identified that the undrained shear strength of normally consolidated samples increases after crossing the phase transformation line because of volume dilation tendency which is not seen in clay. Overconsolidated samples show different soil behavior compared with pure silt due to its tendency of change in volume. It is also found that the overall behavior of Asan marine soil cannot be predicted precisely with the modified Cam-clay model and the bounding surface model.

• Geotechnical Engineering
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• v.11 no.3
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• pp.43-54
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• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated soil and to confirm the application'of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. The application of the model to silty sands is confirmed by the comparison between test and predicted results. During drying -wetting and loading -unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. Predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsaturated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore. recommended to study the behavior of dilatancy for an unsaturated soil.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.59-67
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• 2005

This paper presents experimental and numerical research results of centrifuge model tests performed to investigate the geotechnical engineering behavior of slag compaction pile as a substitute of sand compaction pile. For centrifuge model tests, bearing capacity of composit soil improved with slag compaction piles, stress concentrations in-between pile and soft clay, settlement characteristics, and failure modes were investigated with slags differing in their relative density. A slag was found to be a good substitute for a sand since the slag compaction pile model showed a greater yield stress intensity up to $30\%$ than the sand compaction pile model under the identical testing conditions. Stress concentration ratio tended to increase with the relative density of slag pile and the clear shear lines in the piles were observed at the depth of $2D{\sim}2.5D$ (D=dia. of model pile) from the top of the piles after loading tests. Numerical analysis with a software of CRISP, implemented with the modified Cam-clay model, was carried out to simulate the results of centrifuge model test. Test results about characteristics of load-settlement curves and stress concentration ratio are in relatively good agreements with numerical estimations.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.1
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• pp.116-127
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• 1996

This paper dealt with FEM analysis of foundation improved with pack drain. The theory on pack drain was scrutinized and observed values in the field were compared with numerical results. Work site of Kwangyang container pier was selected as a ease study in which measurement of settlement and pore water pressure was accurately carried out. Biot's consolidation equation was selected as governing One, coupled with modified Camclay model as constitutive one. Christian and Boehmer's numerical technique was adopted. Behavior of foundation with pack drain is not simple but very complicated. Discontinuity resulted from rigidity difference between adjacent materials, smear effect and complicated boundary conditions should be considered in the behavior analysis of foundation behavior. The results of numerical analysis were influenced by smear zone. In relevant to this effect, finite element analysis was carried out using the reduced horizontal coefficient of permeability in the smear zone; The numerical results were compared with observed values in surface settlement. including pore water pressure. However only lateral di5plaoement by numerical ana1Ysis was shown since its measurement was not performed in the field. The predication of settlement to be developed later can be effectively employed for the obtimization of construction. The predication of residual settlement using the data measured in the field was made by Hoshino, Asaoka and hyperbolic method. Among them, the hyperbolic method proved best one. Settlements accorded well between numsrical and observed values while pore pressure showed a slight difference. Lateral displacement showed largest values at constant distance from ground surface. The validation of foundation analysis improved with pack drain by computer program employed in this study selecting modified Cam-clay model was satisfactorily secured.