• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5C
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• pp.177-183
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• 2012

The use of energy pile foundation has been increased for economic utilization of geothermal energy. In particular, a coil-shaped ground heat exchanger (GHE) is preferred than conventional U-shaped heat exchanger to ensure better efficiency of heat exchange rate. This paper presents experimental results by changing different pitch spaces of spiral coils. Joomunjin sand was filled in a steel box of which the size was $5m{\times}1m{\times}1m$. Thermal response tests (TRTs) were conducted to measure the ground thermal conductivity with temperatures of circulating water using line source model and ring coil model. Experimental results and analytical solutions were compared to validate the applicability of these models. Ring coil model showed more accurate similar results with experimental data rather than line source model and cylindrical source model.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.5-15
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• 2013

The end bearing capacity of rock-socketed drilled shafts under axial loading is investigated by Hoek-cell tests and a numerical analysis. From the test results, it was found that the ultimate end bearing capacity ($q_{max}$) was influenced by pile diameter, rock mass modulus and the spacing of discontinuity. A new ultimate end bearing capacity method is proposed by taking end bearing capacity influence factors, including rock mass discontinuity, based on field data. Through comparisons with other field data, the proposed $q_{max}$ method represents a definite improvement in the prediction of ultimate end bearing capacity of rock-socketed drilled shafts.

• Journal of the Korean Geotechnical Society
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• v.38 no.9
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• pp.53-67
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• 2022

Micropiles are cast-in-place-type piles with small diameters. They are widely used for the foundation reinforcement of existing buildings and structures because this technique is easy to construct and economic. A base expansion structure is developed following the mechanism of radial expansion at the pile tip under compression. Numerical analysis, durability tests, and centrifuge tests have been conducted using the base expansion structure. In this study, three-dimensional numerical modeling was performed to describe the behavioral mechanism of the base expansion structure using steel bar penetration under compressive loading, and numerical analyses using centrifuge test conditions were performed for the comparative studies. Additionally, the base structure was modified based on the results of lab-scale analyses, and the bearing capacities of micropiles were compared using field-scale numerical analyses under various ground conditions.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.61-70
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• 2011

The impact protection system consists of an arrangement of circular sheet pile cofferdams-denoted dolphin structuredeeply embedded in the seabed, filled with crushed rock and closed at the top with a robust concrete cap. Centrifuge model tests were performed to investigation the behaviors of dolphins in this study. Total 7 quasi-model tests and 11 dynamic model tests were performed. The main experimental results can be summarized as follows. Firstly, The experimental force-displacement results for quasi-static tests show a limited influence on the initial stiffness of the structure from the change in fill density and the related change in the stiffness of the fill. And by comparing the dissipation at the same dolphin displacement it was found that the denser fill increase the dissipation by 16% for the 20m dolphin and by 23% for the 30m dolphin. The larger sensitivity for the large dolphin is explained by a larger contribution to the dissipation from strain in the fill. In low level impacts the dynamic force-response is up to 26~58% larger than the quasi-static and the dissipation response is showed larger in small displacement. Hence, it is concluded conservative to use the quasi-static response characteristics in the approximation of the response, and it is further concluded that the dolphin resistance to low level impacts is demonstrated to be equivalent and even superior to the high level impacts.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.5-10
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• 2013

Bearing capacity of a drilled shaft can be separated into side resistance and base resistance. But in domestic design procedure side resistance is usually underestimated compared with base resistance. Results of bi-directional test showed that measured side resistances in each different layers are larger than those evaluated from several suggested methods. In this study, measured side resistances in each different layer of drilled shafts installed in domestic sites are analyzed and compared with evaluated side resistances from the method using revised SPT N value. For weathered rock and soft rock layer, from which rock core can hardly be obtained, we suggested new evaluated methods using revised SPT N value instead of the method using uniaxial compressive strength of rock. Resuts showed that the ranges of side resistance of cohesive and non-cohesive layer are $f_s{\leq}5tf/m^2$ and $f_s{\leq}15tf/m^2$ respectively. Range of side resistance in weathered rock is $15tf/m^2$ < $f_s{\leq}50tf/m^2$ and that in soft rock $f_s{\geq}35tf/m^2$.

• Journal of the Korea Fashion and Costume Design Association
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• v.23 no.1
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• pp.37-45
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• 2021

This study observed the release of microplastics according to washing weights and filtering conditions, measured microplastic generation rates, fiber lengths, and fiber diameters. This study attempted to present data for the development of filters that decrease microplastic generation. For test samples, polyester piled knit fabric (cut-pile) was selected, which currently has the highest amount of consumption in the clothing industry, but can easily cause marine pollution because of its low biodegradability. For test equipment, a drum washer was used and microplastics were collected using two filter pore sizes, 5 ㎛ and 20-25 ㎛. Microplastic fibers weights and lengths were measured. The results of the experiment showed the following: 1) The release of microplastics differed according to the fabric weights and washing process; 2) washing fabric weights showed a differences in the collection amount according to the filter pore size (5 ㎛, 20-25 ㎛); 3) observations of differences in the lengths of the microplastics that occur during the washing process by filter pore size were made. Fibers with shorter lengths appeared with filter pore sizes of 5㎛ in comparison to filter pore sizes of 20-25㎛. The results from this study on microplastic generation by fabric during washing, demonstrated the following conclusions that can be used to reduce the release of microplastics. First, the release of microplastics according to fabric weights and washing courses are affected by physical force. Therefore, it is necessary to reduce the amount of physical force due to water flow, increase the fabric weight, or wash the material in low temperatures. Second, in the manufacturing of washing machines, microplastic filtration can be promoted or legislatation supporting microplastic filtration can be introduced.

• Journal of the Korean Geosynthetics Society
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• v.14 no.4
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• pp.87-96
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• 2015

Geosynthetics are widely used in different ways such as reinforcement of structures in road, railway, harbor and dam engineering, drainage, separation and erosion prevention. They are especially applied to reinforced retaining wall and slope or ground reinforcement. Recently, geosynthetics reinforced pile supported (GRPS) embankment was developed to improve stability and construability of embankments in railway engineering. Extension strains are usually measured by strain gauges adhered to geosynthetics to evaluate the stability of geosynthetics. However, the measurements are influenced by manufacturing method and stiffness of geosynthetics and also adherence of strain gauge. In this study, wide-width tensile strength tests were performed on three types of geosynthetics including geogrid, woven geotextile and non-woven geotextile. During the test, strains of geosynthetics were measured by both video extensometer and strain gauges adhered to the geosynthetics and the measured results were compared. Results show that the measured results by strain gauges have high reliability in case of large stiffness geosythetics like geogrid and woven geotextile, whereas they have very low reliability for small stiffness geosythetics like non-woven geotextile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.6
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• pp.825-836
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• 2022

Micropiles can be used to support additional load in extended building structures. However, their use brings about a risk of exceeding the bearing capacity of existing piles. In this study, pre-compression was applied to distribute the load of an existing building to micropiles, and an indoor loading test was performed to confirm the structural applicability of a wedge-type anchorage device designed to improve its capacity. According to the test results, the maximum strain of the anchorage device was 0.63 times that of the yield strain, and the amount of slip generated at the time of anchorage was 0.11 mm, satisfying structural standards. In addition, using MIDAS GTS, a geotechnical finite element analysis software, the effect of the size of the pre-compression, the thickness of the soil layer, and the ground conditions around the tip on the reaction force of the existing piles and micropiles were analyzed. From the numerical analysis, as the size of the pre-compression load increased, the reaction force of the existing pile decreased, resulting in a reduction rate of up to 36 %. In addition, as the soil layer increased by 5 m, the reduction rate decreased by 4 %, and when the ground condition at the tip of the micropile was weathered rock, the reduction rate increased by 14 % compared with that of weathered soil.

• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.43-56
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• 2018

Vertical cutoff walls such as steel pipe sheet piles (SPSPs) have been commonly applied for the construction of the offshore waste landfill site. Because the SPSPs are sequentially installed by connecting their joints to those of adjacent piles, their mechanical stability should be ensured against the inherent external forces on the sea. The objective of this study is to evaluate the structural performances of the newly developed types of SPSP joint compared with those of other joint types. The problems of the traditional SPSP joints are investigated, and an advanced joint shape of SPSP, which is named double H with L-T (DHLT) joint, are designed for improving the constructability and maintenance. Full-scale models of the DHLT joint are manufactured, and then its joint areas are filled with grout material. After 28 days of curing time, compressive and tensile strength tests were performed on the joint models and the test results were compared with those of the traditional joints. Experimental results show that the structural capacities of the DHLT joint models are lower than those of traditional joints due to the influence of grout and steel members. In the cases of the compressive strength test, especially, bending occurs on steel H-beam with no distinct cracks in grout due to the asymmetrical structure of joint which has no reaction force. This study shows that the performance of the SPSP joint can be improved by considering the influence factors on the structural capacities estimated by the experimental tests.

• Journal of the Korean GEO-environmental Society
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• v.14 no.1
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• pp.43-51
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• 2013

Recently, engineering problems such as long-term settlement, differential settlement, and the resultant structural damage, have been frequently reported at construction sites. Use of Sand Compaction Piles(SCP) and Granular Compaction Piles(GCP) are good at remedying existing problems, improving bearing capacity and promoting consolidation. However, such compaction piles have the potential for clogging, which would limit their usability. Investigations into the potential for clogging in SCP, GCP, and GCP mixed with sand has not been thoroughly conducted and is the objective of this current study. Large scale direct shear tests were performed on sections of SCP, GCP, and sand mixed GCP to evaluate bearing capacity. Discrete Element Method analyses were conducted with PFC3D and Finite Element Analyses were conducted with MIDAS GTS to propose an algorithm to help reduce clogging in the granular compaction piles. Results from the large scale direct shear test and multiple simulations suggest a 70% gravel and 30% sand mixing ratio to be optimal for bearing capacity and reducing clogging.