• Journal of the Korean GEO-environmental Society
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• v.8 no.4
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• pp.27-39
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• 2007

This paper investigates numerically characteristics of the fluid flow in spatially correlated variable-aperture fractures under effective normal stress conditions. Spatially correlated aperture distributions are generated by using the geostaistical method (i.e. Turning Bands algorithm). In order to represent a nonlinear relationship between the effective normal stress and the fracture aperture, a simple mechanical formula is combined with a local flow model. Obtained numerical results indicate that the fluid flow is significantly affected by the geometry of aperture distribution varying according to the applied effective normal stress as well as the spatial correlation length of aperture distribution. Moreover, by using results simulated in this study, the modified Louis formula representing the relationship between the effective normal stress and the effective permeability of fracture is proposed.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.89-98
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• 2006

In this paper the behavior of saturated sand deposits where liquefaction occurred before is studied for successive earthquakes. The relationship between past pore pressure generation and reliquefaction resistance is examined by using cyclic direct simple shear tests. If the soil sample in direct simple shear produced nearly 90% of excess pore pressure during first time loading, its liquefaction resistance increased during following cyclic loading after consolidation. However, a fully liquefied soil during first time loading has a densely packed condition but shows less liquefaction resistance for the following cyclic loading. UBCSAND model that can account for pore pressure change and stiffness loss of soil during shaking is used to analyze the centrifuge test simulating reliquefaction. The pore pressure rise during first time cyclic loading controls liquefaction resistance. The measurements from reliquefaction centrifuge test are compared with numerical predictions. By considering frequent earthquakes having occurred at the Southern Korea near Japan, such effective stress approach is necessary for reliquefaction study.

• Journal of the Korean Geotechnical Society
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• v.39 no.9
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• pp.5-11
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• 2023

In analyzing geotechnical structures, the analysis fields are becoming increasingly diversified. In particular, the need for predicting the thermal behavior of ground materials has become important in fields related to soil freezing. To ensure a reliable assessment of the freezing behavior of the ground, considering the variation in the effective thermal conductivity of soil specimens under various conditions is crucial. In this study, probe experiments were conducted by varying the porosity, initial degree of saturation, and read time settings of the meter. Next, the factors influencing the effective thermal conductivity of the frozen sandy soil were evaluated. The experimental results conducted under different porosity conditions showed a tendency for the effective thermal conductivity of frozen soil to increase as the specimen's porosity decreased. However, as the degree of saturation of the specimen increased, the effective thermal conductivity also increased. The sensitivity of the meter's read time setting to the measurement of effective thermal conductivity was observed. When the read time was set to 1 min, the measured values were in a range similar to that obtained in previous studies conducted in Korea with the same soil specimen.

• Journal of the Korean GEO-environmental Society
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• v.8 no.3
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• pp.59-65
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• 2007

Excess pore pressures in low permeability soils may not dissipate quickly enough and decrease the effective stresses inside the soil, which in turn may cause a reduction of the shear strength at the interface between the soil and the reinforcement in MSE walls. For this condition the dissipation rate of pore pressures is most important and it varies depending on wall size, permeability of the backfill, and reinforcement length. In this paper, a series of numerical analysis has been performed to investigate the effect of those factors. The results show that for soils with a permeability lower than $10^{-3}cm/sec$, the consolidation time gradually increases. The increase in consolidation time indicates the decrease in effective stress thus it will result in decrease in pullout capacity of the reinforcement as verified by the numerical analyses. It is also observed that larger consolidation time is required for longer reinforcement length (longer drainage path).

• Geotechnical Engineering
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• v.6 no.4
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• pp.65-74
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• 1990

This paper presents triaxial test (CIVC and CKOUC) results on normally consolidated deep sea clay samples. Based on the test results the pore pressure-strain relations for both isotropicaly and anisotropicaly consgidated samples are expressed with hyperbolic functions of the major princpal strain. The analysis of the difference in pore pressure behavior due to the anisotropy in consolidation stress is carried out with the effective stress pathos of CIVC and CKOUC and finds a factor which correlates the pore pressure of two types of test.

• 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 Korean Tunnelling and Underground Space Association
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• v.6 no.1
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• pp.41-50
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• 2004

The numerical investigation for the effects of blasting-induced vibration on adjacent dam and pore water pressure fluctuation was conducted through solid-water coupled analysis under dynamic loading. The stability of dam was examined by peak particle velocity of core. Pore water pressure distributions were calculated by steady state flow analysis using coupled analysis on ground water and blasting-induced vibration. The influence of pore water pressure and the effective stress distribution in the ground were also investigated. Furthermore, effective stress alteration was examined by applying Finn & Byrne Model to monitor the generation and dissipation of pore water pressure.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.86-86
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• 2020

수리구조물에 관한 기존 연구들은 대부분 기능성과 안정성 측면에서 본체에 작용하는 유체력에 대한 안정성에 주안점을 두고 있다. 수리구조물 상·하류의 수위차에 기인한 기초지반내의 흐름 및 간극수압 변화는 하천 구조물의 안정성을 연구하는데 매우 중요하다. 해양에서는 파랑하중에 의한 과잉간극수압이 액상화를 발생시켜 해안구조물의 안정에 큰 영향을 미치는 것으로 보고되며, 이에 관련 연구들이 활발하게 진행되고 있다. 반면, 하천구조물 주변 지반의 흐름 및 간극수압 뿐 아니라, 액상화에 관한 연구는 아직 미진한 실정이다. 본 연구에서는 수리구조물 주변의 유동 및 와동 현상 뿐 아니라, 수위차에 따른 지반 내부 유동장과 간극수압에 관한 특성을 분석하기 위해 유체-구조물-지반 비선형 상호작용을 고려할 수 있는 수치수조를 새롭게 제안하였다. 그리고 제안하는 수치수조의 타당성 및 유효성을 검증하기 위해 기존 실험값과 비교·검토를 수행하였고, 그 결과는 거의 유사한 경향을 나타내었다. 또한 이 수치수조에 다양한 입사조건(상·하류 수위차)에 적용하여 유체-구조물-지반의 비선형동적상호간섭 해석을 수행하였다. 최종적으로 수치수조에서 측정한 구조물 주변의 유동, 와동, 수위로부터 수리특성을 논의하였다. 게다가 지반내의 흐름과 간극수압을 측정하여 상·하류 수위차가 수리구조물의 안정성에 미치는 영향을 분석할 수 있었다.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.5-14
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• 2009

This study is to analyze numerically the spatial behaviors of the solute transport in a spatially correlated variable-aperture fracture under the effective normal stress conditions. Numerical results show that the solute transport in a fracture is strongly affected by the spatial correlation length of apertures and applied effective normal stress. According to increasing spatial correlation length, the mean residence time of solute is decreased and the tortuosity and Peclet number (is a dimensionless number relating the rate of advection of a flow to its rate of diffusion) is also decreased. These results mean that the geometry of the aperture distribution is favorable to the solute transport as the spatial correlation length is increased. However, according to the applied effective normal stress is increased, the mean residence time and tortuosity have a tendency to increase but the Peclet number is decreased. The main reason that the Peclet number is decreased, is that the solute is displaced by one or two channels with relatively higher local flow rate due to the increment of contact areas by increasing effective normal stress. Moreover, based on numerical results of the solute transport in this study, the exponential-type correlation formulae between the mean residence time and the effective normal stress are proposed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2C
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• pp.83-94
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• 2008

In this study an effective stress analysis was performed to evaluate liquefaction potential and ground settlement for reclaimed sites. The effective stress model can simulate the stiffness degradation due to excess pore pressure and resulting ground deformation. It is applicable to a wide range of strain. An equivalent linear analysis suitable for low strain levels was also carried out to compare the effective stress analysis. Shear stress ratio calculated from an equivalent linear analysis was used to determine SPT blow count to prevent liquefaction. Depending on the magnitude of potential earthquake and fine contents, the SPT blow count was converted into an equivalent cone tip resistance. It was compared with the measured cone tip resistance. The measured elastic shear wave velocity and cone tip resistance from two reclaimed sites in Incheon were used to perform liquefaction analyses. Two liquefaction evaluation methods showed similar liquefaction potential which was evaluated continuously. The predicted excess pore pressure ratio of upper 20 m was between 40% and 70%. The calculated post-shaking settlement caused by excess pore pressure dissipation was less than 10 cm.