• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.863-868
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• 2004

The use of oyster shells is proposed as a substitute construction material for geotechnical applications. To investigate recycling possibility as a substitute of sand compaction pile (SCP) for oyster shells, the geotechnical characteristics including permeability and shear strength of crushed oyster shell, sand and crushed oyster shell-sand mixted soil. Experimental results show that the crushed oyster shells are lighter than sand in weight, and have similar characteristics on permeability to sand. The results of direct shear test show that the measured value of friction angle ${\Phi}$ of crushed oyster shell was lager than that of sand. It would be expected that more angular particles (crushed oyster shells) would interlock more thoroughly than rounded particles (send).

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.482-489
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• 2009

Various model piles with different sections such as reinforced concrete, steel, steel-concrete composite without rebar and steel-concrete composite with rebar were made, and vertical load test was conducted using a large scaled UTM(Universal Test Machine) to evaluate Young's modulus and ultimate load of the model piles. Based on the tests, ultimate load of steel-concrete composite pile is 31% greater than the sum of it of reinforced concrete pile and it of steel pile. This is caused that ultimate load and Young's modulus of inner concrete increase due to confining effect by outer steel casing. Variation of ultimate load is also insignificant depending on the ratio of length to diameter(L/D), therefore bucking has not an effect on change of ultimate load in case of the L/D below 10.

• 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.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.7-17
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• 2018

Test bed additional wall combined with PHC-W pile retaining wall has been constructed. To determine the dimensions of test bed additional wall, bending and shear tests of full scale core members of additional wall were tested. Basement additional walls utilizing PHC-W pile retaining wall, which were developed by modifying the cross-section of PHC piles, were classified into the composite additional wall and the non-composite additional wall. Their tests were conducted to obtain bending strength and shear strength of basement additional walls ultilizing PHC-W pile retaining wall. Since bending strengths and shear strengths of the composite additional wall and the non-composite additional wall were similar, it could be confirmed that the non-composite additional wall could be applied instead of the composite additional wall. Full-scale model additional wall was 200 mm thick, thus the thickness of additional wall combined with PHC-W pile retaining wall could be reduced by 100~200 mm.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.399-410
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• 2015

Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.71-79
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• 2012

Sand compaction pile and stone column replacement methods have been commonly used for improving soft ground in the nearshore. Recently, DCM (Deep cement mixing) method, which can harden soft clays by mixing with cement, is more popularly used in such soft ground improvement. Sandy soils also exist in the seashore. Therefore, in this study, the effect of salinity in sea water and curing methods on the strength of cemented sand was evaluated in terms of unconfined compressive strength (UCS). The sand was mixed with five different cement ratios and distilled water or sea water, and then compacted into a cylindrical specimen. They were cured for 3 days under sea water for DCM construction condition and air cured for onshore curing condition. When a specimen was cured under sea water without confinement, it was easily collapsed due to initiation of cracks. When the cement ratio and curing method were the same, the UCS of the specimen without sea water was at maximum 3.5 times higher than those with sea water. The sea water used for mixing sand had more influence on strength reduction than the sea water used for curing. When the cement ratio was the same, the UCS of air-cured specimen was at average 2 times higher than those of water-cured specimen, regardless of water used.