• Geomechanics and Engineering
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• v.8 no.5
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• pp.707-726
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• 2015

This paper investigates the time dependent behaviour of Haarajoki test embankment on soft structured clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. To analyse the PVD-improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using three different approaches. The construction and consolidation of the embankment are analysed with the finite element method using a recently developed anisotropic model for time-dependent behaviour of soft clays. The constitutive model, namely ACM-S accounts for combined effects of plastic anisotropy, interparticle bonding and degradation of bonds and creep. For comparison, the problem is also analysed with isotropic Soft Soil Creep and Modified Cam Clay models. The results of the numerical analyses are compared with the field measurements. The results show that neglecting effects of anisotropy, destructuration and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the matching methods accurately predict the consolidation behaviour of the embankment on PVD improved soft clays and provide a useful tool for engineering practice.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.35-45
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• 2001

Bergado에 의해 비교 분석된 많은 연구자들의 배수재의 소요통수능에 대한 제안값을 보면 0.32~50cc/s로 그 차이가 너무 크기 때문에 실무에 적용하기가 어렵다. 본 연구에서는 배수재의 통수능변화를 고려할 수 있는 압밀해석방법을 개발하고, 흙의 압밀계수, 압축지수, 배수재 타설심도 및 타설후 시간경과에 따른 배수재의 통수능 감소 등의 현장여건을 고려한 압밀해석을 통하여 압밀지연을 일으키지 않는 배수재의 소요통수능에 대한 기준을 제시하였다. 압밀해석결과 어느값 이상의 통수능에서는 압밀지연이 없으므로 이 값 이상의 통수능을 갖는 배수재를 선택하는 것이 중요하며, 압밀지연시간 5% 이내인 배수재의 소요통수능은 압밀계수($c_{v}$ ), 배수재의 길이(L) 및 압축지수($C_{c}$)와 비례관계로서 안전율 1.5를 고려하여 $q_{wa}$ =8$\times$($c_{v}$ $\times$L$\times$$C_{c}$)(cc/s) 이상이면 되는 상관식을 얻었다. 이 값 이상의 배수재를 선택하는 경우는 연직배수공법의 압밀해석에서 배수재의 통수능을 고려하지 않아도 된다는 결론을 얻었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.605-610
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• 2011

Soft ground improvement is essential to enhance strength of ground for construction in reclaimed land or shore. There are many method of soft ground improvement, and vertical drain method was widely used in many countries including korea. As vertical drain method is to plant many Prefabricated Vertical Drains in soft ground, it promotes consolidation and enhances strength. The PBD(Plastci Board Drain) that is excellent economy and workability was widely used in many countries as Prefabricated Vertical Drains. Construction quality of PBD is affected installation depth, pressure, perpendicularity. This paper describes the system developed that can automatically measure installation depth, pressure and perpendicularity for PBD. This system can reduce fraction defective of construction by auto faulty alarm and keeps the safety of operator by auto control system.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.373-382
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• 2007

In the vertical drain method, discharge capacity is generally one of the most important factor which affect on the estimation of the drain efficiency. However, adopting the drain considering discharge capacity only is not sufficiently considered method so that systematic criteria for adoption is necessary to choose the most suitable drain. Therefore, this study represents the application method considering behavior of the ground and vertical drain which is coupled together and ground improvement efficiency analyzing various cases of discharge capacity test performed in the recent soft ground improvement projects. According to the analysis, most drains tend to satisfy the required discharge capacity. It presents that deformed shape of the drains and well resistance estimation along the ground settlement, improvement efficiency by water content ratio along the depth and shear strength obtained after ground improvement should be considered altogether with the discharge capacity to select the proper drain. Also, appropriate adoption of drain material considering the ground condition is vital through analyzing the field measured data and comparing the result of the discharge capacity test as various vertical drain materials are being constructed continuously.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.103-111
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• 2012

In this study, the full-scale laboratory model test on utilization of recycled aggregates and crushed stone as vertical drains to use an alternative material of sand in soft ground is performed. The settlement and pore water pressure were measured to evaluate the discharge capacity and filed application, and the results were compared and analyzed through the finite element method. The measured and estimated settlement in all vertical drain materials decreases gradually with the load increase. The measured settlement 6.55~8.63 mm, and the estimated by the Hyperbolic model was 7.45~7.92 mm. So the model used for the analysis can be applied to the settlement estimation of the actual field. The variations of pore water pressure with time showed constantly regardless of the load in all vertical drainage materials. The pore water pressure was similarity to that of sand after rapid drawdown. Therefore, it was applicable to the field because discharge capacity was enough to be an alternative material to the sand which had been being used as the vertical drains.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10a
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• pp.105-105
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• 2003

Theoretical studies have been performed for drainage and filtration characteristics, low consolidation rate of sandmat and prefabricated horizontal and vertical drain. Discussion on quality control and methodology, cost analysis for sandmat and prefabricated horizontal drains were performed.

• Korean Journal of Agricultural Science
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• v.37 no.1
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• pp.97-104
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• 2010

In this study, a laboratory model test on utilization of recycled aggregates and crushed stone as vertical drains to use alternative material of sand in soft ground is performed. The vertical and horizontal coefficient of permeability of the recycled aggregates and crushed stone showed largely 1.2~4.0 times and 3.0~3.3 times greater than sand, respectively. Therefore, it showed enough to be an alternative material to the sand which had been being used as the vertical and horizontal drainage material before. The variations of pore water pressure with time showed constantly regardless of the load in all vertical drainage materials. When water level drops suddenly, the pore water pressure of the recycled aggregate and crushed aggregate is reduced to nearly zero. Therefore, it was applicable to the field because discharge capacity was similarity to that of sand. The settlement in crushed aggregates and recycled aggregate decreases gradually with the load increase. When water level drops suddenly, earth pressure in all drains materials was evaluated the equivalent drainage capacity similarity to sand because it show approaching the nearly zero.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1024-1029
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• 2010

The conventional factor of safety as used in geotechnical engineering does not reflect the degree of uncertainty of the relevant parameters. Then in the geotechnical engineering, there have been efforts to reflect the uncertainties of the geotechnical properties through probabilistic analysis. In this study, a practical method for calculation the second moment reliability index using the optimization tool of a spreadsheet software is introduced. And this methodology was proposed by Low, B. K.(1996). The method is based on the perspective of an ellipsoid that just touches the failure surface in the original space of the variables. The method is applied to vertical drains(PVD) and compared with th result of Monte Carlo Simulation method.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.6
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• pp.1-6
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• 2011

The conventional factor of safety as used in geotechnical engineering does not reflect the degree of uncertainty of the relevant parameters. Then in the geotechnical engineering, there have been efforts to reflect the uncertainties of the geotechnical properties through probabilistic analysis. In this study, a practical method for probabilistic analysis using the Hasofer-Lind reliability index is introduced. The method is based on the perspective of an ellipsoid that just touches the failure surface in the original space of the variables. The method is applied to prefabricated vertical drains (PVD) and compared with the result of Monte Carlo Simulation method.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1400-1407
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• 2005

There are a number of approaches to in situ remediation that are used at contaminated sites for removing contaminants from the contaminated zone without excavating the soil. These include soil flushing, dual phase extraction, and soil vapor extraction. Of these techniques, soil flushing is the focus of the investigation in this paper. The concept of using prefabricated vertical drains(PVDs) for remediation of contaminated sites with fine-grained soils is examined. The PVD system is used to shorten the drainage path or the groundwater flow and promote subsurface liquid movement expediting the soil flushing process. The use of PVDs in the current state of practice has been limited to soil improvement. The use of PVDs under vacuum conditions is investigated using sample soil consisting of silty sand.