• Journal of the Society of Disaster Information
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• v.15 no.1
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• pp.84-97
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• 2019

Purpose: The consolidation settlement of soft ground is dependent on the distribution of pore water pressure which is also affected by hydraulic conductivities (boundary condition) of layers, thickness of clayey soil layer and surcharge. Results: However, the current consolidation analyses are mostly based on Terzaghi's consolidation theory that assumes the initial pore water pressure ratio with depth to be constant. In this study, numerical analysis are carried out to investigate the variation of pore water pressure dissipation with depth and thickness of clayey soil layer, time, surcharge as well as drainage conditions. Conclusion: Comparative study with Terzaghi's consolidation theory is also conducted. The result shows that Terzaghi's consolidation theory should be used with caution unless it is ideally corresponded to the isochrone.

• Geotechnical Engineering
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• v.2 no.1
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• pp.15-26
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• 1986

Consolidated undrained standard triaxial tests for two remoulded clays and one undisturbed clay were carried out in order to find out the relationship between excess pore water pressure and axial strain in mortally consolidatated saturated clays during undrained shear. Tests were performed with isotropically-normally consolidated specimens by strain controlled and stress controlled loading. As the result of this stud!'a hyperbolic function expressing the relationship between pore water pressure and strain was found out, and it showed the same form as the Kondner's hyperbolic function for stress·strain behaviour. Two parameters used for the function can be obtained by CU-triaxial test.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.871-873
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• 2009

기존의 연직 배수공법은 통수능의 저하, 막힘현상(clogging) 등으로 인하여 연약지반의 압밀을 지연시키는 문제점을 가지고 있다. 이 연구에서는 고분자 압전소자인 PVDF(polyvinylidene fluoride)를 연직배수공법에 적용하여 연직배수공법의 기존 문제점을 극복하고 연약지반의 간극수를 빠르게 소산시킴으로서 압밀을 촉진 시킬 수 있을 것이라 판단되어 이에 따른 실내 실험을 수행하였다. 실험 결과 PVDF를 적용한 경우에서 그렇지 않은 경우보다 간극수의 배출량이 증가하여 PVDF의 적용으로 배수재의 성능이 향상됨을 알 수 있었다.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.5-19
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• 2012

Vertical drains along with the preloading technique have been commonly used to enhance the consolidation rate of dredged placement formation. In practice, vertical drains are usually installed in the process of self-weight consolidation of a dredged soil deposit because this process takes considerable time to be completed, which makes conventional analytical or numerical models difficult to quantify the consolidation behavior. In this paper, we propose a governing partial differential equation and develop a numerical model for 2-D axisymmetric non-linear finite strain consolidation considering self-weight consolidation to predict the behavior of a vertical drain in the dredged placement foundation which is installed during the self-weight consolidation. In order to verify the developed model in this paper, results of the numerical analysis are compared with that of the lab-scaled self-weight consolidation test. In addition, the model verification has been carried out by comparing with the simplified method. The comparisons show that the developed model can properly simulate the consolidation of the dredged placement formation with the vertical drains installed during the self-weight consolidation. Finally, the effect of construction schedule of vertical drains and of pre-loading during the self-weight consolidation is examined by simulating an imaginary dredged material placement site with a thickness of 10 m and 20 m, respectively. This simulation infers the applicability of the proposed method in this research for designing a soil improvement in a soft dredged deposit when vertical drains and pre-loading are implemented before the self-weight consolidation ceases.

• Geotechnical Engineering
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• v.14 no.6
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• pp.93-112
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• 1998

In the present study, 2-D consolidation theory of the dredged clay by means of the horizontal drain method is proposed. The horizontal drain method to install the drains such as plastic drain board within the dredged clay is a soil improvement method to accelerate the consolidation by expelling pore water in the vertical direction along the horizontal drains. Based on the finite strain consolidation theory by Gibson et al., the partial differential equation of 2-D consolidation due to the horizontal drain is derived. The consolidation due to the horizontal drain can be illustrated from combined self-weight consolidation effect and consolidation effect by horizontal drains. For the prediction of consolidation settlement and degree of consolidation numerical analysis is suggested on the basis of Dufort-Frankel finite differential algorithm. Also, the analytical procedures proposed in this study are verified by the model tests, and the predictions of the consolidation settlement and degree of consolidation are compared with the results obtained from the tests for the dredged clay gathering at Siwha site in Ansan, Korea. For the predictions, the relationship void ratio vs effective stress and the relationship permeability vs void ratio of the dredged clay are obtained from the odometer tests. Additionally, the parametric study for consolidation settlement by variations of design parameters related with horizontal drain method is carried out. Based on the results of the parametric study, design .charts for the preliminary design are also proposed.

• Journal of the Korean Geosynthetics Society
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• v.3 no.1
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• pp.17-25
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• 2004

A horizontal drain method, which applies vacuum pressure at the end of a horizontal drain for discharging pore water, is used often for improving surface reclaimed clay in the field. In this study, to examine the effectiveness of improving consolidation or shear strength depends by varying vacuum pressure, laboratory chamber horizontal drain test using vacuum pressure is performed and the results is compared with that of self-weight consolidation. The results show that water content reduces with the increase of soil depth in case of self-weight consolidation, while it reduces near the horizontal drain and increases with the increase of the distance from the horizontal drain in case of applying vacuum pressure. The shear strength of dredged soil was improved as well, when the vacuum pressure is applied. The optimized consolidation was achieved at the vacuum pressure range of 30 to 50kPa in the laboratory box test of 50cm wide, considering the range of drain interval in the field was between 0.7 and 1.2m.

• Journal of the Korean GEO-environmental Society
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• v.11 no.3
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• pp.43-51
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• 2010

In the downstream areas of the Nakdong river, Pusan clays are commonly found and thickness may reach to maximum of 100m. From geological point of view, Pusan clay are characterized as holocene clays, deposited for approximately 20,000 years ago. Recently, there have been many construction projects based on these soft ground areas. It is needed to know clearly soil properties of the areas for design and safety analysis, especially undrained shear strength of soft clays. However, Pusan clay have not been studied systematically because the clay layers are usually very deep, having high sensitivity characteristic. In this study, undisturbed UD samples obtained from the downstream areas of the Nakdong river were researched using laboratory tests (CthUE, CKcUC, CIUC, UU and UC) and in-situ tests (Field Vane, CPTu). The undrained shear strength characteristics of the samples were depicted using stress-strain relationship.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1229-1241
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• 1994

This study aims at investigating the undrained behavior of the normally consolidated clay foundation using single hardening constitutive model based on elasticity and plasticity theories. The specimen employed was sampled at Mooan near the down stream of Young San river and remolded into consolidation apparatus. 11 soil parameters for the model was determined from simple tests such as isotropic compression and consolidation undrained triaxial compression tests. FEM program to predict the undrained behavior of the foundation was developed and back analysis was performed to verify prediction ability of the FEM program. Finally plate load test on the 2-dimensional model foundation was carried out in order to compare numerical analysis and observed values on the foundation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3713-3718
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• 2012

The relations of the various undrained geotechnical properties were, in depth, investigated for highly plastic soils using the numerous experimental testing results. The sensitivity is proportional to void ratio and OCR but inversely proportional to effective unit weight. The difference in Su(Un), Su(UU), and Su(FV) tends to increase or decrease with such sensitivity, void ratio, and OCR. The possibility of deducting the empirical equations denoting the correlations of various properties and the indicator for selecting appropriate testing method could be confirmed.

• 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.