• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.17-28
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• 2010

Vertical drains are commonly used to accelerate the consolidation process of soft soils, such as dredged materials, because they additionally provide a radial drainage path in a deep soil deposit. In practice, vertical drains are commonly installed in the process of self-weight consolidation of a dredged soil deposit. The absence of an appropriate analysis tool for this situation makes it substantially difficult to estimate self-weight consolidation behavior considering both vertical and radial drainage. In this paper, a new method has been proposed to take into account both vertical and radial drainage conditions during nonlinear finite strain self-weight consolidation of dredged soil deposits. For 1-D nonlinear finite strain consolidation in the vertical direction, the Morris (2002) theory and the PSDDF analysis are adopted, respectively. On the other hand, to consider the radial drainage, Barron's vertical drain theory (1948) is used. The overall average degree of self-weight consolidation of the dredged soil is estimated using the Carillo formula (1942), in which both vertical and radial drainage are assembled together. A series of large-scale self-weight consolidation experiments being equipped with a vertical drain have been carried out to verify the analysis method proposed in this paper. The results of the new analysis method were generally in agreement with those of the experiments.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.373-381
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• 2005

The permeability of contaminated soil and elapsed time are important considering factors to in-situ soil remadiation. Gabr et. al. (1996) derived the solution equation of contaminant concentration ratio as initial one (C/$C_0$) with time and spatial changes in contaminated area which embedded with vertical drains. The contaminant concentration ratio (C/$C_0$) is analyzed with time and spatial changes in three different permeability areas which are $k=l.0{\times}10^{-5,}$ $l.0{\times}l0^{-6,}$ $l.0{\times}l0^{-7}\;_{m/s}$ by using the Gabr's equation. Results from numerical analysis indicate that the ratio (C/$C_0$) decreases as the elapsed time increases in every point, however, remediation efficiency decreases as the analyzing point is far from injection well to extraction one and is deeper from top level of contaminated area. And also it decreases as the permeability of contaminated area decreases. Especially, the lower permeability of contaminated area effects directly on the soil remediation, in this research, under condition which the permeability of contaminated area is $l.0{\times}l0^{-7}\;_{m/s}$, the maximum time needed to attain 90% clean up level ($t_{90}$) is 65,690 hours(7.5 years), it takes so much time to clean the low permeability contaminated soil.

• Geomechanics and Engineering
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• v.1 no.4
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• pp.275-289
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• 2009

Electroosmosis (EO) is the movement of water in a porous medium under the influence of a direct current (dc). In past decades, electro-osmosis has been successfully employed in many soil improvement and other geotechnical engineering projects. Metal electrodes, such as steel, copper and aluminum have been used traditionally to conduct current. The shortcoming of these electrodes is that they corrode easily during an EO treatment, which results in reduced effectiveness and environmental concerns. More recently, conductive polymers are developed to replace metal electrodes in EO treatment. Electrical vertical drainages (EVDs) are one of these products under trial. The goal of this study is to assess the performance of EVDs for soil improvement and to further understand the scientific principle of the EO process, including the voltage drop at the soil-EVD interface, electrical current density, polarity reversal, and changes in soil physico-chemical properties generated by electroosmosis. It is found from the study that after 19 days of EO treatment with a constant applied dc electric field intensity of 133 V/m, the soil's moisture content decreased by 28%, the shear strength and pre-consolidation pressure increased more than 400%. It is also found that the current density required triggering the water flow in the soil tested, the Korean Yulchon marine clay, is 0.7 $A/m^2$. The project demonstrates that EVDs can serve as both electrodes and drains for soil improvement in short term. However, the EVDs, as tested, are not suitable for polarity reversal in EO treatment and their service life is limited to only 15 days.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.02a
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• pp.62-70
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• 1999

Artesian pressure exists in Yangsan site, the maximum value of which has been measured as high as 5 t/m$^2$. This paper deals with the prediction of consolidation settlement for the site with artesian pressure. The consolidation settlement at the site has been accelerated using vertical band drains. Since the artesian pressure gives lower effective stress than a static condition, its effect should be considered in the settlement prediction. This case study shows that the prediction of settlement and pore pressure dissipation agrees well with the measurements, when considering the artesian effect.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.357-364
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• 2000

This paper starts with reviewing general patterns of deformation of the soft ground with by embankment. Correlation between lateral and vertical deformation of soft ground under embankment are analyzed and discussed by comparing the performance of the Yangsan test embankment on treated soft ground with vertical drains.

• Geomechanics and Engineering
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• v.7 no.5
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• pp.525-537
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• 2014

The typical design of ground improvement with prefabricated vertical drains (PVD) and surcharge preloading involves a series of deterministic analyses using averaged or mean soil properties for the various combination of the PVD spacing and surcharge preloading height that would meet the criteria for minimum consolidation time and required degree of consolidation. The optimum design combination is then selected in which the total cost of ground improvement is a minimum. Considering the variability and uncertainties of the soil consolidation parameters, as well as considering the effects of soil disturbance (smear zone) and drain resistance in the analysis, this study presents a stochastic cost optimization of ground improvement with PVD and surcharge preloading. Direct Monte Carlo (MC) simulation and importance sampling (IS) technique is used in the stochastic analysis by limiting the sampled random soil parameters within the range from a minimum to maximum value while considering their statistical distribution. The method has been verified in a case study of PVD improved ground with preloading, in which average results of the stochastic analysis showed a good agreement with field monitoring data.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.376-381
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• 1998

The large scaled field test by prefabricated vertical drains was performed to evaluate the superiority of vertical discharge capacity for drain materials through compare and analyze the time-settlement behavior with drain spacing and the compression index and consolidation coefficient obtained by laboratory experiments and field monitoring system 1. The relation of measurement settlement( $S_{m}$) versus design settlement( $S_{t}$) and measurement consolidation ratio( $U_{m}$) versus design consolidation ratio( $U_{t}$) were shown $S_{m}$=(1.0~l.1) $S_{t}$, $U_{m}$=(1.13~l.17) $U_{t}$, at 1.0m drain spacing and $S_{m}$=(0.7~0.8) $S_{t}$, $U_{m}$=(0.92~0.99) $U_{t}$ at 1.5m drain spacing, respectively. 2. The relation of field compression index( $C_{cfield}$) and virgin compression index( $V_{cclab}$) was shown $C_{cfield}$=(1.0~1.2) $V_{cclab}$, But it was nearly same value when considered the error with determination method of virgin compression index and prediction method of total settlement. 3. field consolidation coefficient was larger than laboratory consolidation coefficient, and the consolidation coefficient ratio( $C_{h}$/ $C_{v}$) were $C_{h}$=(2.4 ~ 3.0) $C_{v}$. $C_{h}$=(3.5 ~ 4.3) $C_{v}$ at 1.0m and 1.5m drain spacing and increased with increasing of drain spacingngasing of drain spacingng spacingng

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.5
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• pp.133-143
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• 2000

A large scale field test of prefabricated vertical drains was performed to anayze the effect of parameters of the very soft clay at a test site. compression index and the coefficient of horizontal consolidation obtained by back-analysis of settlement data were compared with those obtained by means of laboratory tests. Hyperbolic method, Asaoka meoth and curve fitting method were used to compute final settlement of coefficient of consolidation. The relationships of settlement measurement(Sm) versus design settlement(St) and the measurement consolidation ratio(Um) versus design consolidation (Ut) were shown as Sm=(1.0~1.1) St , Um=(1.13~1.17) Ut at 1.0m spacing of drain and Sm=(0.7~0.8)St, Um= (0.92~0.99) Ut at 1.5 m spacing of drain, respectively . The relationships of the field compression index(CcField) and virgin compression index(vcc lab) were shown as Ccfield =(1.0~1.2)vcc lab . But it was nearly within the same range when considering the error factor with the determination method of virgin compression index and the prediction back-analysis of the settlement data was larger than the coefficient of vertical consolidation, and the ratio of consolidation coefficient (Ch/Cv) was Ch =(2.4~2.9) Cv , Ch=(3.4~4.2) Cv at 1.0m and 1.5m spacing of drain, respectively.

• Journal of the Korean GEO-environmental Society
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• v.6 no.2
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• pp.51-60
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• 2005

The disposal problem of waste lime which is a residual product of lime industry have caused a lots of arguments in the past few years. Further more, waste lime contains a high moisture content which causes the disposal of waste lime is a great difficulty. The purpose of this study is to investigate for the effective dewatering solutions by placing various prefabricated vertical drains. The moisture content and degree of consolidation, pore water pressure, changes of settlement, bearing capacity with various vertical drains in waste lime were analyzed. The laboratory test results indicate that PBD is 2 times higher than circular drain in coefficient of consolidation. Based on the laboratory test results, settlement, pore water pressure, and dewatering measurements are shown in similar tendency. It is considered that PBD can drain primitive pore water much efficiently. The picture of SEM shows that circular drain filter has a serious clogging problem in comparison with PBD. In conclusion, PBD holds a superiority in waste lime's ground improvement and dewatering pore water pressure from the waste lime sludge. Also, circular drain is desired for some modification in its filtering system.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.69-77
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• 2007

In this study, the consolidation behavior of clayey ground improved by vertical drain method was analyzed by the finite difference method based on the three-dimensional elasto-viscous consolidation theory, which can express the behavior of the secondary consolidation without considering the distinction of the normally consolidated and overconsolidated states. And the applicability of the elasto-viscous consolidation theory was discussed by comparing with the test results obtained from the model test of ground improved by vertical drain system. From these results, it is found that the amount of the settlement when the excess pore water pressure almost dissipated in the clay ground with vertical drains became smaller than that of the one-dimensional condition, and then the amount and rate of the residual settlement at secondary consolidation process became larger than those of the one-dimensional condition. finally, the effect of soil parameter on behavior of consolidation process was investigated by the results of a series of numerical analysis for the normalized and overconsoldiated states.