• Proceedings of the KSR Conference
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• 2001.05a
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• pp.459-465
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• 2001

The Prefabricated Vertical Drain(PVD) method is most widely used technique to accelerate the consolidation process and to strengthen the weak clayey soil in situ. Uncertainty in the consolidation process via the Prefabricated Vertical Drain(PVD), and the effects of uncertainty on the design of PVDs, are investigated in this paper, Among the effect factors, the coefficient of horizontal(radial) consolidation, C$\sub$h/, is the most important and sensitivity analysis of the degree of consolidation with respect to the other effect factors are carried out. For the reliable determination of uncertain quantities, the laboratory and in-situ tests are carried out. Henceforth, probability analysis that take the uncertainty into account are executed and reliable design method is provided in practice.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.1
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• pp.24-29
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• 2000

We propose a simple method to control the crystallization depth of amorphous silicon (a-Si) deposited by PECVD or LPCVD during the excimer laser annealing (ELA). Employing the new method, we have formed poly-Si/a-Si double film and fabricated a new poly-Si TFT with vertical a-Si offsets between the poly-Si channel and the source/drain of TFT without any additional photo-lithography process. The maximum leakage current of the new poly-Si TFT decreased about 80% due to the highly resistive vertical a-Si offsets which reduce the peak electric field in drain depletion region and suppress electron-hole pair generation. In ON state, current flows spreading down through broad a-Si cross-section in the vertical a-Si offsets and the current density in the drain depletion region where large electric field is applied is reduced. The stability of poly-Si TFT has been improved noticeably by suppressing trap state generation in drain region which is caused by high current density and large electric field. For example, ON current of the new TFT decreased only 7% at a stress condition where ON current of conventional TFT decreased 89%.

• 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.

• Journal of the Korean GEO-environmental Society
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• v.8 no.3
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• pp.27-33
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• 2007

The vertical drain method recently being used in Korea is one of the popular soft ground improvement methods, and it is divided into the sand drain method, the pack drain method, the paper drain method, and the PBD method according to the drainage. However, these methods generate the disturbed zone called the smear zone when the drainage is penetrated into the in-situ ground. The characteristics of the smear zone generated cause the problems that the coefficient of permeability decreases, and then the consolidation time in the design becomes longer than expected. Even though the coefficient of horizontal consolidation and the coefficient of permeability in the smear zone are very important design factors directly influencing the degree of consolidation, in the existing studies, these coefficients have been empirically derived by the coefficient of vertical consolidation and used for the design. However, in case that these coefficients derived by the coefficient of vertical consolidation are applied to the actual design, a loss of the duration of construction and a loss of economical efficiency can be happened because of the inaccuracy of the coefficient of horizontal consolidation and the coefficient of permeability. Hence, in this study, in order to understand such influence, the laboratory test was carried out so as to reasonably determine the coefficient of permeability and the coefficient of consolidation in diverse ground conditions. Then, the range of smear effect on clay and silt was estimated with monitoring data through the laboratory test.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09b
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• pp.3-12
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• 2010

Vertical drains have been commonly used to increase the rate of the consolidation of dredged material. The installation of vertical drains additionally provides a radial flow path in the dredged foundation. The objective of this study develops a numerical model for 2-D axisymmetric non-linear finite strain consolidation considering self-weight consolidation to predict the effect of vertical drain in dredged foundation which is in process of self-weight consolidation. The non-linear relationship between the void ratio and effective stress and permeability during consolidation are taken into account in the numerical model. The results of the numerical analysis are compared with that of the self-weight consolidation test in which an artificial vertical drain is installed. In addition, the numerical model developed in this paper is the simplified analytical method proposed by Ahn et, al (2010). The comparisons show that the developed numerical model can properly simulate the consolidation of the dredged material with the vertical drains installed.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.743-749
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• 2009

In this study, the field test for suction drain method which does not require a surcharge load and a sealing sheet was performed at west seashore's site constructed by the dredged and reclaimed clay. The improvements of soft ground by suction drain method was analyzed by the results of real-time field measurement, SPT(Standard Penetration Test) and laboratory tests. The results indicated that the soft ground improvement is effective the vertical drain method used with vacuum pressure rather than surcharge load with considering settlements, dissipation of pore water pressure and shear strength.

• 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.8 no.3
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• pp.35-40
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• 2007

The vertical drain method recently being used in Korea is divided into the sand drain method, the pack drain method, the paper drain method, and the PBD method according to the drainage. However, these methods generate the disturbed zone called the smear zone when the drainage is penetrated into the in-situ ground. The characteristics of the smear zone generated cause the problems that the coefficient of permeability decreases and the consolidation time becomes longer than expected in the design. Although the size of the smear zone is a very important factor directly influencing the degree of consolidation, in the existing studies, the general value for the size of the smear zone proposed has been used in the design. However, the size of the smear zone proposed by the existing studies cause a loss of economical efficiency because of the inaccuracy of the design. Hence, in this study, the characteristics on the size of the smear zone were analyzed by carrying out the three dimensional numerical analysis and the method to determine the conversion size of the smear zone considering the change of the coefficient of permeability was proposed in order to consider the change of the coefficient of permeability in the actual design.

• Journal of Industrial Technology
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• v.26 no.B
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• pp.83-92
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• 2006

A probabilistic analysis model. one of reliability analysis methods introducing the concept of variables, was developed to investigate the uncertainty of dominant factors influencing the degree of consolidation in the radial consolidation theories. Based on the developed probabilistic analysis model, sensitivity study of those factors was performed to find their trends of affecting the degree of consolidation in the vertical drain method. Various radial consolidation theories, proposed by Barron(1948), Hansbo(1979), Yoshikuni(1979) and Onoue(1988), were used for this parametric study with the influencing factors such as size of smear zone, reduction ratio of permeability in the smear zone, discharge capacity, permeability for horizontal flow and coefficient of consolidation for horizontal flow. As results of this sensitivity study, for the given consolidation theory, contribution of each factor to the degree of consolidation was figure out and compared to each other. For the given value of each factor, the sensitivity to the degree of consolidation in the various theories was evaluated and their applicability and limitations were assessed.

• Journal of the Korean GEO-environmental Society
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• v.8 no.2
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• pp.49-55
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• 2007

It is very important to determine the consolidation rate of ground, depending on the progress of time in applying this vertical drain method. Various consolidation analysis solutions capable of forecasting the consolidation rate are being proposed at the moment. However, the degree of consolidation measured from site, has a considerable different from the degree of consolidation which was obtained by the analysis of vertical drain consolidation. This study aims at assessing the applicability and verfication of each consolidation analysis solution by comparing and analyzing the degree of consolidation measured in the field and the degree of consolidation based on the theoretical equation for the analysis of the consolidation of Hansbo, Onoue, Zeng and Xie used as the consolidation analysis solution before the beginning of construction, on the basis of monitored field results and site investigation data as to the deep soft ground in Busan area applied by PBD method.