• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.361-375
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• 2015

An energy pile is one of the novel ground heat exchangers (GHEX's) that is a economical alternative to the conventional closed-loop vertical GHEX. The combined system of both a structural foundation and a GHEX contains a heat exchange pipe inside the pile foundation and allows a working fluid circulating through the pipe, inducing heat exchange with the ground formation. In this paper, a group of energy piles equipped with parallel U-type (5, 8 and 10 pairs) heat exchange pipes was constructed in a test-bed by fabricating in large-diameter cast-in-place concrete piles. In addition, a closed-loop vertical GHEX with 30m depth was constructed nearby to conduct in-situ thermal response tests (TRTs) and to compare with the thermal performance of the cast-in-place energy piles. A series of thermal performance tests was carried out with application of an artificial cooling and heating load to evaluate the heat exchange rate of energy piles. The applicability of cast-in-place energy piles was evaluated by comparing the relative heat exchange efficiency and heat exchange rate with preceding studies. Finally, it is concluded that the cast-in-place energy piles constructed in the test-bed demonstrate effective and stable thermal performance compared with the other types of GHEX.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.111-123
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• 2010

The steel pipe of steel-concrete composite drilled shafts increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, pile loading tests were performed to analyze the field applicability of a steel-concrete composite drilled shafts. The test ground consisted of 5~7 m thick soil underlying rock mass. The test piles consisted of two steel-concrete composite drilled shafts, which were the concrete filled steel pipe piles with the diameter of 0.508 m, and a concrete pile with the same diameter. The test results showed that the boundary between the upper steel composite section and the lower concrete section was structurally weak and needs to be reinforced by using a inner steel cage. If the boundary is located in deep depth, which is not influenced by lateral load, the allowable strength of the lower concrete section increases, so an economical design can be performed by increasing the design load of steel-concrete composite drilled shafts.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.35-42
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• 2011

The residual stress on drilled shafts is often neglected. Neglect of the existence of locked-in loads in the shaft is the main reason for conclusions of instrumented tests which suggest that shaft resistance is smaller when the shaft is loaded in tension than when it is loaded in compression. A few researchers studied the residual stress and mentioned that the residual stress is influenced by either the physical expansion/contraction of concrete during the curing or site stratigraphy. In this study, field measurements of residual stress on test shafts were conducted and the factors influencing the residual stress were figured out.

• 레미콘
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• no.6 s.28
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• pp.118-121
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• 1991

• Journal of the Korean GEO-environmental Society
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• v.7 no.1
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• pp.19-28
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• 2006

In Korea, none of the design methods, which can consider the properties of hard soil, weathered rock and the condition of construction, are suggested. Therefore, the properties of geomaterial are simply classified into three categories such as sand, clay and rock for the resistance estimation of axially loaded drilled shafts in Korea. However, in America, O'Neill et al.(1996) presented design methods for a new category of geomaterial which is between soil and rock termed "intermediate geomaterials, IGM's". And FHWA(1999) adapted above most complete classification of geomaterials in its design manual. However, in Korea, these properties are depended on the engineer's judgement, the weathered rocks may be counted as soils, although they may be referred to as IGM's in America. In this study, the applicability of IGM method was investigated through the three construction sites in Korea. For the comparison, two geomaterial properties are applied, respectively. The one was sound soil condition and the other was IGM condition and classical design method and IGM method were applied, respectively. The results showed that the predicted bearing capacities of drilled shafts with IGM's were larger than the predicted values by the classical design method with sound soil condition.

• Journal of the Korean GEO-environmental Society
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• v.6 no.2
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• pp.61-73
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• 2005

In Korea, none of the design methods, which can consider the properties of hard soil, weathered rock and the condition of construction, are suggested. Therefore, the properties of geomaterial are simply classified into three categories such as sand, clay and rock for the resistance estimation of axially loaded drilled shafts in Korea. However, in America, O'Neill et al.(1996) presented design methods for a new category of geomaterial which is between soil and rock termed "intermediate geomaterials, IGM's". And FHWA(1999) adapted above most complete classification of geomaterials in its design manual. However, in Korea, these properties are depended on the engineer's judgement, the weathered rocks may be counted as soils, although they may be referred to as IGM's in America. In this study, the applicability of IGM method was investigated through the two construction sites in Korea. For the comparison, two geomaterial properties are applied, respectively. The one was sound soil condition and the other was IGM condition and classical design method and IGM method were applied, respectively. The results showed that the predicted bearing capacities of drilled shafts with IGM's were larger than the predicted values by the classical design method with sound soil condition.

• Journal of the Korean GEO-environmental Society
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• v.2 no.4
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• pp.5-14
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• 2001

The NDT(Non-Destructive Testing) technique, detecting defects without damaging foundations, has, lately, been a matter of concern. In this study, the applicability of the borehole methods(CSL, CT, PS) and the surface reflection methods(SE, IR) to the evaluation of integrity of drilled shaft was investigated through field test. Ten drilled shafts, 0.4 m in diameter and 7.0 m long each, were constructed, one shaft with no defect and nine shafts intentionally with the combination of the common defects such as soft bottom, necking, bulging, cave-in, and/or weak concrete. Analysing each NDP test result on the constructed drilled shafts, an optimum combination of the NDP methods as well as the applicability of each NDP method to detecting defects of drilled shaft have been investigated.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.399-408
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• 1997

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.207-215
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• 2002

This study is focusing on mixing the foamed concrete incorporated by waste expanded polystyrene(W-EPS), investigating the physical properties and offering a proper quality control method to the field engineers. Two types of W-EPS (type A and type B) were studied. Type A (B) had globular (crushed) shape and diameter of 3-5 (1-2) mm. The results show that the flow was suddenly reduced with increasing mixing quantity of two types, but it satisfies KS F 4039 until 60 ％ of mixing rate. In general, the absorption rate was suddenly reduced with increased mixing quantity of two types especially, in type A. Apparent specific gravity was 0.36∼0.53 and reduced with increasing mixing quantify of type A. But it increased in case of type B. Compressive strength and heat conduction rate increased with mixing with W-EPS than non-mixing W-EPS but reduced with mixing too much W-EPS. Based ong the results, it is believed that mixing with W-EPS can improve the recycle of industrial wastes and produce the high quality foamed concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1915-1933
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• 2013

In this study, the virtual fixed point analysis and 3D fully modeling analysis for bent pile structures are conducted by considering various influencing factors and the applicability of the virtual fixed point theory is discussed. Also, the optimized column-pile length ratio is analyzed for supplementing virtual fixed point design and examining a more exact behavior of bent pile structures by taking into account the major influencing parameters such as pile length, column and pile diameter, reinforcement ratio and soil conditions. To obtain the detailed information, the settlement and lateral deflection of the virtual fixed point theory are smaller than those of 3D fully modeling analysis. On the other hand, the virtual fixed point analysis overestimates the axial force and bending moment compared with 3D fully modeling analysis. It is shown that the virtual fixed point analysis cannot adequately predict the real behavior of bent pile structures. Therefore, it is necessary that 3D fully modeling analysis is considered for the exact design of bent pile structures. In this study, the emphasis is on quantifying an improved design method (optimized column-pile length ratio) of bent pile structures developed by considering the relation between the column-pile length ratio and allowable lateral deflection criteria. It can be effectively used to perform a more economical and improved design of bent pile structures.