• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1264-1273
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• 2010

Soil-bentonite cutoff walls are widely recognized to be the effective barrier for containment of wastes and groundwater. Bentonite cake is usually found remaining on the trench surface due to the use of bentonite slurry during the excavation for the cutoff wall construction. Defects also inevitably take place due to the inappropriate construction procedures or improperly mixed soil-bentonite backfill. The defects include insufficient keys and windows in the soilbentonite cutoff wall. In this study, the performance of the soil-bentonite cutoff wall is evaluated based on the flow rates through the wall. Three-dimensional numerical models were applied to simulate the groundwater flow through the soil-bentonite cutoff walls of typical geometries with consideration of the defects and bentonite cake. Results of the simulations showed that the bentonite cake has no effect in the insufficient key cases. In the keyed wall cases, the bentonite cake with very low hydraulic conductivity significantly impedes the flow of groundwater through the wall. The presence of the bentonite cake not only compromises the window defect but also renders the wall construction more effective in blocking the groundwater flow. These findings show the significance of the bentonite cake in a soil-bentonite cutoff wall construction.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1478-1486
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• 2009

As a conventional line-fitting method, the Bouwer and Rice method has been popularly adopted to estimate the hydraulic conductivity of an aquifer through a slug test. Because a ventical cutoff wall is usually very compressible and features a small wall thickness, the Bouwer and Rice method should be carefully used for the vertical cutoff wall. In addition, a relatively impermeable layer, called a filter cake, formed at the interface between the cutoff wall and the natural soil formation makes it difficult to use the Bouwer and Rice method directly. In order to overcome such limitations, the original Bouwer and Rice method is modified by incorporating the concept of the flow net method. In this modification, the geometry condition of cutoff walls including the filter cake is effectively considered in evaluating the hydraulic conductivity of a vertical cutoff wall.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.47-55
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• 2009

As a conventional line-fitting method, the Bouwer and Rice method has been popularly adopted to estimate the hydraulic conductivity of an aquifer through a slug test. Because a vertical cutoff wall is usually very compressible and features a small wall thickness, the Bouwer and Rice method should be carefully applied to analyzing slug test results to estimate the hydraulic conductivity of vertical cutoff walls. In addition, a relatively impermeable layer, called a filter cake, formed at the interface between the cutoff wall and the natural soil formation makes it difficult to use the Bouwer and Rice method directly. In order to overcome such limitations, the original Bouwer and Rice method has been modified by incorporating the concept of the flow net method. In this modification, the geometry condition of cutoff walls including the filter cake is effectively considered in evaluating the hydraulic conductivity of a vertical cutoff wall.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.220-228
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• 2008

In constructing a slurry trench cutoff wall, a thin but relatively impermeable layer called filter cake can be formed on the excavation surface. The filter cake significantly influences the result of slug test analysis in the cutoff wall. This study is to examine the effect of filter cake on evaluating in situ hydraulic conductivity of the vertical cutoff wall along with slug test analyses. The numerical program Slug_3D was modified to take filter cake into account in the slug test simulation. With consideration of filter cake, the type curve method and the modified line-fitting method were used to reanalyze the case study taken from a landfill site. The previous results achieved by Choi and Daniel (2006b) without consideration of filter cake have been compared with the results in this study. The considerable difference between the two results shows the necessity of considering the filter cake in practice.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.105-116
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• 2011

No analytical solution exists for evaluating in-situ hydraulic conductivity of vertical cutoff walls by analyzing slug test results. Recently, an analytical solution to interpret slug tests has been proposed for a partially penetrated well in an aquifer. However, this analytical solution cannot be directly applied to the cutoff wall because the solution has been developed exclusively for an infinite aquifer instead of a narrow cutoff wall. To consider the cutoff wall boundary conditions, the analytical solution has been modified in this study to take into account the narrow boundaries by introducing the imaginary well theory. Two boundary conditions are considered according to the existence of filter cakes: constant head boundary and no flux boundary. Generalized steady-state shape factors are presented for each geometric condition, which can be used for evaluating the in-situ hydraulic conductivity of cutoff walls. The constant head boundary condition provides higher shape factors and no flux boundary condition provides lower shape factors than the infinite aquifer, which enables to adjust the in-situ hydraulic conductivity of the cutoff wall. The hydraulic conductivities calculated from the analytical solution in this paper give about 1.2~1.7 times higher than those from the Bouwer and Rice method, one of the semi-empirical formulas. Considering the compressibility of the backfill material, the analytical solution developed in this study was proved to correspond to the case of incompressible backfill materials.

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.17-31
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• 2012

No analytical solution exists for evaluating in-situ hydraulic conductivity of vertical cutoff walls by analyzing slug test results with consideration of transient flow. There is an analytical solution proposed to interpret a slug test performed in a partially penetrated well within an aquifer. However, this analytical solution cannot be directly applied to the cutoff wall because the solution has been developed exclusively for an infinite aquifer instead of a narrow cutoff wall. To consider the cutoff wall boundary conditions (i.e, constant head boundary and no flux boundary condition), the analytical solution has been modified in this study to take into account the narrow boundaries by introducing the imaginary well theory. Type curves are constructed from the currently derived analytical solution and compared with those of a partially penetrated well within an aquifer. The constant head boundary condition provides faster hydraulic head recovery curve than the aquifer case. On the other hand, no flux boundary condition leads to slower hydraulic head recovery. The bigger the shape factor and deviation of the well and the smaller the width of the vertical cutoff wall are, the more effect of boundary condition was observed. The type curves obtained from the analytical solution for a cutoff wall are similar to those made by the numerical method in the literature.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.121-131
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• 2008

In constructing a slurry trench cutoff wall, bentonite-water slurry is used to secure the stability of sidewalls during excavation before the wall is completed by backfilling. Unexpectedly, a thin but relatively impermeable layer called filter cake can be formed on the excavation surface, which significantly influences the result of slug test analysis in the cutoff wall if not considered. This study is to examine the effect of filter cake on evaluating hydraulic conductivity of the vertical cutoff wall through slug test analysis with the aid of the verified numerical program Slug_3D. The no-flux boundary conditions were adopted in Slug_3D to simulate the filter cake on the interface between the wall and the natural soil. A new set of type curves were built for applying the type curve method. New modification factors were obtained for using the modified line-fitting method. With consideration of filter cake, the type curve method and the modified line-fitting method were adopted to reanalyze the case study taken from EMCON (1995). The previous results achieved by Choi and Daniel (2006) without consideration of filter cake were compared with the present results obtained in this paper. The comparison emphasizes the necessity of considering filter cake when analyzing slug test results in vertical cutoff walls.

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.163-174
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• 1999

This paper presents a case history of remedial action adopted for contaminated groundwater in a landfill. The objectives of the projects are : (1) to effectively confine contaminated groundwater with an economically reasonable means, (2) to prevent further contamination of soil by collecting and treat the contaminant. and (3) to assure the environmental safety of the landfill during its operating period. Reported are the process from site investigation, through design and construction of an appropriate remedial action, to the monitoring of the selected confinement system. In view of the results of site investigation, deep soil mixing cutoff wall using the DMW(deep soil mixing cutoff wall) method and specially produced HEC soil stabilizer were used for the construction of deep soil mixing cutoff wall. For rock foundation with sever fractures, chemical grout curtain with urethane was installed. The monitoring results to date indicate that the selected vertical barrier performed satisfactorily.

• Journal of electromagnetic engineering and science
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• v.16 no.3
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• pp.164-168
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• 2016

A dual-band through-the-wall imaging radar receiver for a frequency-modulated continuous-wave radar system was designed and fabricated. The operating frequency bands of the receiver are S-band (2-4 GHz) and X-band (8-12 GHz). If the target is behind a wall, wall-reflected waves are rejected by a reconfigurable $G_m-C$ high-pass filter. The filter is designed using a high-order admittance synthesis method, and consists of transconductor circuits and capacitors. The cutoff frequency of the filter can be tuned by changing the reference current. The receiver system is fabricated on a printed circuit board using commercial devices. Measurements show 44.3 dB gain and 3.7 dB noise figure for the S-band input, and 58 dB gain and 3.02 dB noise figure for the X-band input. The cutoff frequency of the filter can be tuned from 0.7 MHz to 2.4 MHz.

• Journal of the Korean Geotechnical Society
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• v.35 no.8
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• pp.5-15
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• 2019

This study was conducted to propose a reasonable requirement regulation of cutoff barriers composed of bottom layer and vertical barrier of offshore landfill for the prevention of contaminant leakage. The bottom layer was composed of impermeable clay layer; vertical walls were composed of double walls; outer wall was composed of steel sheet pile which registed against outer force; cutoff vertical barrier took the role of inner wall. Seepage-advection-dispersion numerical analysis was conducted using SEEP/W and CTRAN/W programs under steady and unsteady flows. The results showed that the values calculated under steady flow showed higher migration of pollutant than those of unsteady flow. The values calculated under steady flow are more valid from a design point of view. Under steady flow and the bottom clay layer and when the vertical barrier are homogeneous and completely well installed, respectively, the minimum required cutoff regulations for hydraulic conductivity, thickness, and embedded depth of the bottom clay layer and vertical barrier were suggested.