• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.209-220
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• 2001

준설매립지반 표층강도증진을 위한 수평진공배수공법 적용시의 압밀현상 예측을 위한 연구를 수행하였다. 초연약지반에 수평배수재와 진공압을 이용하여 수평진공배수 공법을 적용할 경우, 배수재 부근에서 3차원적 배수특성과 넓은 범위의 유효응력의 변화, 지반의 압축성 및 투수성이 크게 변화하게 된다. 이를 위하여 3차원 배수특성과 다양한 경계조건, 부의 간극수압 발생을 통한 유효응력의 증가, 유효응력에 따른 압축성과 투수성의 비선형성을 포함할 수 있도록 기존의 3차원 압밀 지배방정식을 확장 유도하였고, 유효응력-간극비-투수계수의 관계를 누승형태의 함수로 표현하여 사용하였다. 해석기법의 타당성을 검증하기 위하여 실내에서 수행된 대형 토조실험 결과를 모델링하여 좋은 일치를 확인하였고, 이를 바탕으로 수평진공배수공법 적용시의 압밀효과에 대한 분석결과 드레인이 타설된 상부지반에서는 균등한 개량효과의 결과를, 하부의 미개량 지반에서는 자중압밀에 의한 압밀효과를 확인할 수 있었으며 배수재의 수평타설 간격에 따른 압밀효과 분석을 통하여 적정 배수재 설치간격의 범위를 확인하였다.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.133-140
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• 2005

In order to accelerate the rate of consolidation settlement and gain a required shear strength for a given soft clay deposit, vertical drain method combined with a preloading technique has been widely applied. In this paper, a theory of axisymmetric nonlinear consolidation fer drainage-installed deposit, which considers secondary compression (or creep) during primary consolidation, as well as the variations of compressibility and permeability during the consolidation process, has been developed. A computer program named AXICON based on Hypothesis B fur the analysis of axisymmetric nonlinear consolidation was developed by adopting finite difference method. The results of AS(ICON were compared with Hansbo's solution based on Hypothesis A, as well as in-situ settlements and pore pressures measured in test embankment of Ska-Edeby. The results indicated that Hypothesis A usually underestimated the in-situ settlement and Hypothesis B was considered to be logically correct. It was also shown that one may able to appropriately predict the real in-situ behaviors using the proposed program.

• Geotechnical Engineering
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• v.9 no.1
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• pp.21-30
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• 1993

To know the importance of soil paramters which are used to estimate the deformation and porepressure of soil, the sensitivity for soil parameters in elastic analysis is analyzed. Using the consolidation teat results of several cohesive soils, soil parameters are estimated by back analysis method, and from the parameters the deformations and porepressures of the soil are estimated by elastic analysis, In elastic analysis for soil-deformation and porepressure, the sensitivity for the Young's modulus is large, and the esimation of Young's modulus is more important in pro- portion to the size of stress. Using the measured results during initial short period in small stress, the soil parameters can be correctly estimated by back analysis method. To decrease the iteration number in back analysis and to get the better paramters, the initial measurements in more nodes are required and the more accurate initial measurements are required.

• Geotechnical Engineering
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• v.13 no.1
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• pp.137-146
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• 1997

In this study, a large consolidation test was carried out to estimate the consolidation behaviour of dredged clay ground improved by horizontal drain using plastic board drain with a vacuum pressure. The test results were analyzed by a numerical simulation using potential consolidation theory applied to a hollow cylinder. The rapid decreases in pore pressure and the drain speed in the plastic board indicate that the consolidation occurred quickly after the vacuum state was applied to the test soil. According to the numerical analysis obtained by applying the linear potential consolidation theory to a clay hollow cylinder with external radial drainage, the pore pressure is affected by the strain and the permeability of the soil rather than by the diffusion types. Therefore, measured surface settlement agreed with the numerical solution at the point where consolidation pressure increasing rate u: -0.5. Also the behaviour of the clay layer settlement in the place where the drain was installed was similar to that shown in Barron's consolidation theory. Finally, the design and construction procedure including the selection of the appropriate arrangement of horizontal drains were discussed based on the results of the laboratory tutsts. It is also shown that the potential consolidation theory make it possible to predict consolidation behaviour in the field using horizontal drains exactly.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.5-13
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• 2007

Many construction projects adopt grouting technology to prevent the leakage of groundwater or to improve the shear strength of the ground. Recognition as a feasible field procedure dates back to 1925. Since then, developments and field use have increased rapidly. According to improvement of grout materials, theoretical study on grout penetration characteristics is demanded. Fluid of grout always tends to flow from higher hydraulic potential to lower one and the motion of grout is also a function of formation permeability. Viscosity of pout is changed by chemical action while grout moves through pores. Due to the increment of viscosity, permeability is decreased. Permeability is also reduced by grout particle deposits to the soil aggregates. In this paper, characteristics of new cement grout material that has been developed recently are studied: injectable volume of new grout material is tested in two different grain sizes of sands; and the method to calculate injectable volume of grout Is suggested with consideration of change in viscosity and clogging phenomena. The calculated values are compared with injection test results. Viscosity of new grout material is found to increase as an exponential function of time. And lumped parameter $\delta$ of new grout material to be used for assessing deposition characteristics is estimated by comparing deposit theory with injection test results considering different soil types and different injection pressures. Injection test results show that grout penetration rate is decreased by the increase of grout viscosity and clogging phenomena.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.201-207
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• 2006

Soil tests are generally conducted using a membrane to measure a pore water pressure. However, it has also been recognized that the membrane penetrates into the specimen by the change of the confining pressure, and it results in the erroneous measurement in the pore water pressure and the volumetric strain. This study examined the effectiveness of the correction equation of the membrane penetration on the basis of the experimental data acquired during the isotropic unloading and the cyclic shear process using the hollow cylindrical shear test equipment. The results showed that the membrane penetration by the correction equation could be overestimated when the mean effective stress was lower than 20kPa in this study. The limitations originated from the sudden increase near the zero effective stress, and in order to prevent the overestimation in low effective stress condition, the use of the constant a was proposed in this study. Furthermore, the correction equation for the membrane penetration had to be applied carefully when the initial relative density was high and the density changes were occurred by the relocation of the soil particle by the liquefaction.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.25-34
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• 2008

A new hybrid oedometer cell is designed and manufactured to investigate a behavior of soft soils by using elastic and electromagnetic waves during consolidation test. Bender elements, which generate and detect shear waves, are placed in the top cap and the bottom plate and mounted on the oedometer wall. Double wedge type electrical resistance probe, which measures local void ratio change, is positioned onto the top cap of the oedometer cell. The bender elements and the electrical resistance probe are anchored into a nylon set screw with epoxy resin. The nylon set screw with epoxy resin minimizes directly transmited elastic waves through the oedometer cell due to impedence mismatch and allows for easy replacement of defected bender elements and electrical resistance probe. Primary consolidation time can be estimated from the slope of electrical resistance versus log time curve and the evolution of shear wave velocity. The shear wave velocity can be used to assess inherent anisotropy when disturbance effects are minimized because particle alignment affects the shear wave velocity. The void ratios evaluated by the electrical resistance probe are similar to those by the settlement during consolidation. This study suggests that the shear wave velocity and the electrical resistance can provide complementary imformations to understand consolidation characteristics such as primary consolidation, anisotropy, and void ratio.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.59-67
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• 2006

The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of the same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipation time. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

• Journal of the Korean Geotechnical Society
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• v.22 no.1
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• pp.35-44
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• 2006

In general typically granular soils contain a certain amount of fines. It is also widely recognized that foundation soils under working loads show highly non-linear behavior from very early stages of loading. In the present study, a series of laboratory tests with sands of different silt contents are conducted and methods to assess strength and stiffiness characteristics are proposed. Modified hyperbolic stress-strain model is used to analyze non-linearity of silty sands in terms of non-linear Degradation parameters f and g as a function of silt contents and Relative density Dr. Stress-strain curves were obtained from a series of triaxial tests on sands containing different amounts of silt. Initial shear modulus, which is used to normalize Degradation modulus of silty sands, was determined from resonant column test results. From the laboratory test results, it was observed that, as the Relative density increases, values of f decrease and those of g increase. In addition, it was found that values of f and g increase and decrease respectively as a Skeleton void ratio $(e_{sk})$ increases.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.179-191
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• 2000

본 연구에서는 화강토 지반상의 자립식 diaphragm wall의 거동을 연구하기 위하여 벽체의 근입깊이비, 지하수위 및 굴착조건(연속 및 단계굴착)을 변화시키면서 원심모형시럼을 수행하였다. 원심모형실험시 지반굴착은 흙과 동일한 밀도로 혼합된 zine chloride 용액이 배수되도록 밸브를 조작하여 실시하였으며, 굴착에 의해 발생되는 지반의 변형괴 벽체의 변위 및 휨모멘트를 시간경과에 따라 측정하였다. 실험결과, 벽체의 근입깊이비가 증가함에 따라 벽체의 휨모멘트는 증가하는 반면, 굴착과정동안 배면측에서의 간극수압 감소속도는 감소하였다. 최종 굴착단계에서 굴착후 시간경과에 따른 침하량은 굴착과정중의 침하？에 비해 5~7% 정도를 나타내었다. 최대표면침하량과 벽체변위를 굴착깊이로 정규화한 결과 최대 침하량은 벽체 변위량의 0.8~1.2배9평균0.91배)사이에 분포하였다. 굴착깊이로 전규화한 벽체변위와 근입깊이와의 관계는 지수함수식으로 제안하였다. 파괴면은 직선적인 형태로 파괴면내의 배면측 지반은 벽체를 향하여 하향의 변위를 일으키면서 벽체의 회전에 의해 파괴되었으며, 퐈괴면의 각도는 66~72.5$^{\circ}$정도로 이론적인 파괴면의 각도보다 크게 평가되었다.