• Journal of the Korean GEO-environmental Society
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• v.20 no.2
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• pp.19-28
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• 2019

Grounds of the western coast of the Korean Peninsular are mostly composed of soft and cohesive soils, and it is necessary to carry out soil improvement before construction. The CGS (Compaction Grouting System) method has been commonly applied for the purpose of not only improving soft ground but also serving as the pile foundation of a bridge. In this paper, the CGS method was applied to the Incheon International Airport facility site, which consists of reclaimed landfill and soft clay soil, so as to evaluate the applicability of this soil improvement method to soft clay ground formations. Futhermore, results of construction were intensively studied along with a series of field experiments and theoretical consideration. The cone penetration tests were performed to assess the ground improvement effect of the CGS method. Consequently, the application of CGS method led to an increase in soil strength enough to be used as the pile foundation to support the bridge at the site. In addition, the size of the upper grout-bulb was estimated by adopting the cavity expansion theory and compared with that of actual grout bulb exhumed in the field. Therefore, it is proved that the cavity expansion theory can be utilized to predict and evaluate the improvement of soft ground.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.407-414
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• 1999

Sand drain as a vertical drainage is widely used in soft ground improvement. Recently, sand, the principal source of sand drain, is running out. A laboratory model test was carried out to utilize gravel as a substitute for sand. Though which the characteristics of gravel are compared to those of sand for engineering purpose. According to the test, the settlement was found to be smaller in gravel drain than in sand drain. The increase in bearing capacity by gravel rile explains the result. The clogging effect was not found in gravel column. As a result, it is assumed that gravel is relatively acceptable as a drainage material. Gravel material seems better than sand material in bearing capacity and it is found that bearing capacity is larger when gravel is used as compaction pile than as drain from in-situ test on bearing capacity. Increase of bearing capacity with gravel pile means an effect of composite ground by stiffness of gravel material. It can lie supposed to use gravel pile instead of sand pile in view of consolidation effect and bearing capacity.

• 지반과기술
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• v.7 no.2
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• pp.14-22
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• 2010

• Journal of the Korean GEO-environmental Society
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• v.2 no.3
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• pp.57-69
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• 2001

Sand pile is widely used as a ground improvement method. Although the primary purpose of constructing sand pile is accelerating consolidation, composite ground effect also can be gained by constructing sand pile. This study was accomplished to understand composite ground effect on the ground improved by sand piles which were applied as vertical drainage material when area replacement ratio was small relatively. For determining bearing capacities of origin ground and sand piles and analysing interaction between embankment and origin ground, bearing tests and earth pressure monitoring are performed. From the results, it turned out that the contribution of sand pile as a load bearing mechanism is not substantial. However, the bearing capacity of sand pile was increased to sixty percentages when compared with origin ground. The increasement of bearing capacity could be caused the change of consolidation characteristics during the process of consolidation by overburden load. Therefore, the composite ground effects depending on stiffness increasement of sand pile would be estimated as a factor decreasing consolidation settlement.

• Journal of the Korean Geosynthetics Society
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• v.8 no.3
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• pp.9-16
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• 2009

In generally, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. Several calculation methods for bearing capacity for very soft ground improved by geotextile have been proposed already but they are not established yet. In this paper, elastoplastic finite element analysis is carried out to estimate bearing capacity improvement for very soft ground reinforced by geotextile. In conclusion, by reinforcing with geotextile the bearing capacity improvement of very soft ground is increased with the increase of the settlement after yielding. And it is enough that the length of geotextile is about 3~4 times of the loaded width for the effect to the bearing capacity improvement. Finally, the biggest tensile force of geotextile occurs at an edge of the uniform load.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.427-437
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• 2019

The purpose of this study is to improve construction cost, time, and field management when constructing a road on soft soil foundation by eliminating extra-banking of subgrade layer after completion of the consolidation process. The subgrade layer was pre-constructed before the soft ground improvement. And then it was confirmed by the field test that the compaction effect was maintained or not after consolidation settlement. As a result of the experiment, all subgrade layers were kept constant except for the top subgrade layer. So it would be advantageous to secure economical and practical in road construction if subgrade layers were constructed exclusive of the top subgrade layer.

• Journal of the Korean Geotechnical Society
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• v.16 no.2
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• pp.115-123
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• 2000

Piezocone Penetration Test has been performed in the soft ground over the site preparation area at Inchon International Airport(IIA). With the pore pressure dissipation test results, the changes in the permeability and the coefficient of consolidation in clayey soil were checked and the differences of the undrained shear stength verified the soft ground improvement effect from vane test and piezocone test both before and after the improvement. From the results, thin sand seam was found and this caused a big difference in the coefficient of permeability and consolidation. The coefficient of consolidation was high in the upper marine deposit and relatively low in lower marine deposit. It was found that the reduction of void ratio by preloading resulted in the reduction of coefficient of consolidation after the ground improvement. In addition, there were some variations of undrained shear strength when the number of 15 or 18 was used as the coefficient of piezocone(Nkt). However, when the average value of undrained shear strength calculated using Nkt=10 was applied, the result indicated the similar average value with the result of vane test and the increasing rate of strength( Δsu/Δ$\sigma$≒0.38) also showed the similar distribution.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.1-13
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• 2019

The purpose of this study is to examine the effect of soft ground improvement by dynamic replacement with utilizing crushed rock. In order to understand the ground improvement effect when applying dynamic replacement method with crushed rock, the laboratory test and field test were performed. The internal friction angle and apparent cohesion were derived through direct shear test. The dynamic replacement characteristics were identified by analyzing the weight, drop, and number of blows needed for dynamic replacement. Through the field plate bearing test and density test, the bearing capacity and settlement of the improved ground were measured, and the numerical analysis were conducted to analyze the behavior of the improved ground. In this study, it proposes modified soil experimental coefficient(C_DR) to 0.3~0.5 in the dynamic replacement method with crushed rock. Also when applying the dynamic replacement method using crushed rock, the particle size range is less than 100 mm, D₉₀ is less than 80 mm and D₁₅ is more than 30 mm.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.90-99
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• 2004

Stone column is one of the soft ground improvement method, which enhances ground conditions through ground water draining, settlement reducing and bearing capacity increasing complexly by using crushed stone instead of sand in general vertical drain methods. In recent, general construction material, sand is in short of supply, because of the unbalance of demand and supply. Also, the bearing capacity improving effect of stone column method is needed in many cases so the bearing capacity estimation is considered as important point. Nevertheless, adequate estimation methods to predict bearing capacity of stone column considering stone column and improving ground behavior reciprocally is not yet prepared. To contribute this situation, bearing capacity behavior of stone column were simulated as numerically on various property cases of crushed stone and surrounded ground. Through the numerical analysis of simulation results, bearing capacity behavior prediction formula was suggested. This formula was verified by comparing the prediction result with in situ test.

• Journal of the Korean GEO-environmental Society
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• v.15 no.8
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• pp.13-21
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• 2014

The Plastic Board Drain is used to improve soft soils deposited in container terminal area at a port. This paper describes settlement behavior of soft ground in this area from PBD installation to the time of operating facilities. Previous researches focused on soil improvement effect of PBD, that is, the settlement occurred during ground improvement period. The residual settlement occurred during operating the facility is very important from the maintenance and management point of view. However, the study of this residual settlement has been rarely conducted. In this study, by analyzing the measured settlement data obtained from the container terminal area at the port, it was verified that the residual settlement induced during operating facilities occurred in a layer with PBD improvement. In addition, by comparison the settlement predicted by a numerical analysis with the settlement measured in the field, it was confirmed that the actual settlement is in the range of predicted settlement.