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Prof. Hangseok Choi
School of Civil, Environmental and Architectural Engineering, Korea University, Seongbuk-gu, Seoul, South Korea

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0 Heat Exchangers
0 Heat Transfer
0 Heat exchange pipe
0 Heat pump system
0 Heating-cooling cycles

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Heat Exchangers
Heat exchange pipe
Heat Transfer
Heat pump system
Heating-cooling cycles

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Journal article
Published: 21 June 2021 in Colloids and Surfaces A: Physicochemical and Engineering Aspects
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Understanding the transport of naturally abundant clay colloids is critical in colloid associated contaminant transport in porous media. This study was focused on the impact of the median size of sand grains and the ionic strength of solution on the transport and retention behavior of clay colloids. Two clay samples of kaolinite and illite colloids were selected to represent clay samples containing 1:1 and 2:1 clay minerals, respectively. The observed retention profiles and breakthrough curves demonstrated that the impact of ionic strength on the retention behavior of clay was consistent with other colloidal colloids such as latex colloids or graphene oxide. The quantity of the retained clay increased as the median sizes of sand decreased, and the ionic strength increased from 0 to 0.1 M. However, a similar quantity of retained illite at the ionic strength of 0.01 M and 0.1 M indicates the presence of threshold ionic strength in clay colloid retention. The exponential relationship between sand-to-clay size ratio and first-order retention coefficient at given ionic strength implies the chance in long-term prediction of clay colloid transport from the observed retention profiles.

ACS Style

Jongmuk Won; Taehyeong Kim; Minkyu Kang; Yongjoon Choe; Hangseok Choi. Kaolinite and illite colloid transport in saturated porous media. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2021, 626, 127052 .

AMA Style

Jongmuk Won, Taehyeong Kim, Minkyu Kang, Yongjoon Choe, Hangseok Choi. Kaolinite and illite colloid transport in saturated porous media. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2021; 626 ():127052.

Chicago/Turabian Style

Jongmuk Won; Taehyeong Kim; Minkyu Kang; Yongjoon Choe; Hangseok Choi. 2021. "Kaolinite and illite colloid transport in saturated porous media." Colloids and Surfaces A: Physicochemical and Engineering Aspects 626, no. : 127052.

Journal article
Published: 04 May 2021 in Renewable Energy
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The energy slab is a slab structure in a building that encases heat exchangers to utilize geothermal energy for heating and cooling of the building. In the energy slabs, the presence of thermal insulation layers is crucially important compared to those of the conventional Ground Heat Exchanger (GHEX). In this paper, a computational fluid dynamics (CFD) model was developed by calibrating with the result of the in-situ thermal performance test (TPT) to comprehensively assess the effect of influential factors on the thermal performance of energy slabs. Note that the thermal conductivity of ground formations and the flow rate of working fluid significantly influence the thermal performance of energy slabs. Especially in the energy slabs, the existence of a thermal insulation layer with appropriate thermal properties is significantly important to relieve the thermal interference induced by ambient air temperature. Considering the performance of thermal insulation and economic feasibility, a PF (phenol foam) board is found to be the suitable material for the energy slab considered in this paper.

ACS Style

Seokjae Lee; SangWoo Park; Jongmuk Won; Hangseok Choi. Influential factors on thermal performance of energy slabs equipped with an insulation layer. Renewable Energy 2021, 174, 823 -834.

AMA Style

Seokjae Lee, SangWoo Park, Jongmuk Won, Hangseok Choi. Influential factors on thermal performance of energy slabs equipped with an insulation layer. Renewable Energy. 2021; 174 ():823-834.

Chicago/Turabian Style

Seokjae Lee; SangWoo Park; Jongmuk Won; Hangseok Choi. 2021. "Influential factors on thermal performance of energy slabs equipped with an insulation layer." Renewable Energy 174, no. : 823-834.

Journal article
Published: 26 April 2021 in Sustainability
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The present study compares and analyzes three risk analysis models that are applicable to shield tunnel boring machine (TBM) tunneling, and thus proposes an improved risk matrix model based on the causal networks applicable to sustainable tunnel projects. The advantages and disadvantages of three risk analysis models are compared, and causal networks are structured by analyzing the causal relationship between risk factors and risk events. Based on the comparison and analysis results, the causal network-based risk matrix model (CN-Matrix model), which complements the disadvantages and exploits the advantages of the three existing models, is proposed in this paper. Furthermore, this study suggests a means of modifying the weighting scores in the estimation of the risk score, which permits the CN-Matrix model to determine the risk level more reasonably. Thus, the improved CN-Matrix model is more reliable and robust compared to the three existing models.

ACS Style

Heeyoung Chung; JeongJun Park; Byung-Kyu Kim; Kibeom Kwon; In-Mo Lee; Hangseok Choi. A Causal Network-Based Risk Matrix Model Applicable to Shield TBM Tunneling Projects. Sustainability 2021, 13, 4846 .

AMA Style

Heeyoung Chung, JeongJun Park, Byung-Kyu Kim, Kibeom Kwon, In-Mo Lee, Hangseok Choi. A Causal Network-Based Risk Matrix Model Applicable to Shield TBM Tunneling Projects. Sustainability. 2021; 13 (9):4846.

Chicago/Turabian Style

Heeyoung Chung; JeongJun Park; Byung-Kyu Kim; Kibeom Kwon; In-Mo Lee; Hangseok Choi. 2021. "A Causal Network-Based Risk Matrix Model Applicable to Shield TBM Tunneling Projects." Sustainability 13, no. 9: 4846.

Research article
Published: 12 April 2021 in Marine Georesources & Geotechnology
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The performance of a double-core prefabricated vertical drain (PVD), which could reduce the well resistance via its large cross-sectional area and structural stability, was investigated experimentally and numerically. The double-core and the conventional single-core PVD, which has been widely adopted in reclaimed ground improvement, were compared in this study. In the experimental investigation, modified Delft tests and a calibration chamber test were carried out in a laboratory to determine the discharge capacities of the PVDs. Thereafter, single- and double-core PVDs were installed in the Busan New Port site, which had a 40 m thickness of clay deposit, and the performances of the PVDs estimated through surface settlements were compared. In addition, a numerical program named ILLICON was applied with field measurements, and a parametric study was conducted for different discharge capacities of the PVDs. The result of the laboratory tests and field measurements indicated that there was no difference in the performance between the two types of PVDs for improving the soft ground, considering actual ground conditions. Similarly, the parametric study results also implied that both PVDs could be satisfactorily applied in thick reclaimed ground, and there is no significant difference in the performance of single- and double-core PVDs.

ACS Style

Hyobum Lee; Jeonghun Yang; Minkyu Kang; SangWoo Park; Hangseok Choi. Comparison of performance of single- and double-core prefabricated vertical drains for thick reclaimed ground improvement. Marine Georesources & Geotechnology 2021, 1 -13.

AMA Style

Hyobum Lee, Jeonghun Yang, Minkyu Kang, SangWoo Park, Hangseok Choi. Comparison of performance of single- and double-core prefabricated vertical drains for thick reclaimed ground improvement. Marine Georesources & Geotechnology. 2021; ():1-13.

Chicago/Turabian Style

Hyobum Lee; Jeonghun Yang; Minkyu Kang; SangWoo Park; Hangseok Choi. 2021. "Comparison of performance of single- and double-core prefabricated vertical drains for thick reclaimed ground improvement." Marine Georesources & Geotechnology , no. : 1-13.

Regional case study
Published: 27 March 2021 in Journal of Material Cycles and Waste Management
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Attempts have been made to address the strict regulations on eco-friendly construction and recycle aggregate resources, encouraging researchers to consider the utilization of recycled aggregates for the backfilling of underground power systems. It is essential to recognize the physical and thermal characteristics of domestic recycled aggregates for use as backfill materials for underground power conduits in Korea. Herein, the thermal properties of concrete-based recycled aggregates with different grain-size distributions are evaluated, and the particle breakage effect of recycled aggregates is identified through the compaction tests. The thermal properties of the recycled aggregates and the river sand were measured using a transient hot wire method after a standard compaction test. The particle breakage effect was also investigated during the standard compaction test. The thermal resistivities of the recycled aggregates and the river sand showed a similar trend, which were decreased with an increase in the water content at the same dry unit weight. In addition, particle breakage during compaction led to an enhanced compaction effect, reducing the thermal resistivity and increasing the fine particle content. This study shows that the recycled aggregates can be promising backfill materials that substitute natural aggregates when backfilling underground power conduits.

ACS Style

Dongku Kim; Kibeom Kwon; Gyeonghun Kim; Hangseok Choi. Evaluation of Korean recycled aggregates as backfilling underground power system considering particle breakage effect. Journal of Material Cycles and Waste Management 2021, 23, 1665 -1677.

AMA Style

Dongku Kim, Kibeom Kwon, Gyeonghun Kim, Hangseok Choi. Evaluation of Korean recycled aggregates as backfilling underground power system considering particle breakage effect. Journal of Material Cycles and Waste Management. 2021; 23 (4):1665-1677.

Chicago/Turabian Style

Dongku Kim; Kibeom Kwon; Gyeonghun Kim; Hangseok Choi. 2021. "Evaluation of Korean recycled aggregates as backfilling underground power system considering particle breakage effect." Journal of Material Cycles and Waste Management 23, no. 4: 1665-1677.

Journal article
Published: 12 March 2021 in Applied Sciences
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This study demonstrates a three-dimensional numerical simulation of earth pressure balance (EPB) shield tunnelling using a coupled discrete element method (DEM) and a finite difference method (FDM). The analysis adopted the actual size of a spoke-type EPB shield tunnel boring machine (TBM) consisting of a cutter head with cutting tools, working chamber, screw conveyor, and shield. For the coupled model to reproduce the in situ ground condition, the ground formation was generated partially using the DEM (for the limited domain influenced by excavation), with the rest of the domain being composed of FDM grids. In the DEM domain, contact parameters of particles were calibrated via a series of large-scale triaxial test analyses. The model simulated tunnelling as the TBM operational conditions were controlled. The penetration rate and the rotational speed of the screw conveyor were automatically adjusted as the TBM advanced to prevent the generation of excessive or insufficient torque, thrust force, or chamber pressure. Accordingly, these parameters were maintained consistently around their set operational ranges during excavation. The simulation results show that the proposed numerical model based on DEM–FDM coupling could reasonably simulate EPB driving while considering the TBM operational conditions.

ACS Style

Hyobum Lee; Hangseok Choi; Soon-Wook Choi; Soo-Ho Chang; Tae-Ho Kang; Chulho Lee. Numerical Simulation of EPB Shield Tunnelling with TBM Operational Condition Control Using Coupled DEM–FDM. Applied Sciences 2021, 11, 2551 .

AMA Style

Hyobum Lee, Hangseok Choi, Soon-Wook Choi, Soo-Ho Chang, Tae-Ho Kang, Chulho Lee. Numerical Simulation of EPB Shield Tunnelling with TBM Operational Condition Control Using Coupled DEM–FDM. Applied Sciences. 2021; 11 (6):2551.

Chicago/Turabian Style

Hyobum Lee; Hangseok Choi; Soon-Wook Choi; Soo-Ho Chang; Tae-Ho Kang; Chulho Lee. 2021. "Numerical Simulation of EPB Shield Tunnelling with TBM Operational Condition Control Using Coupled DEM–FDM." Applied Sciences 11, no. 6: 2551.

Journal article
Published: 11 March 2021 in Renewable and Sustainable Energy Reviews
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An energy pile is a type of ground heat exchanger (GHEX) that can reduce the initial construction cost by being installed in the existing foundation structure (i.e., pile). However, despite economic benefits, energy piles have not been globally employed owing to a lack of construction cases and appropriate design methods. Therefore, in this study, a design method applicable to large-diameter cast-in-place energy piles was developed and verified by conducting long-term monitoring on the heating and cooling operation. In addition, to evaluate the applicability of the cast-in-place energy piles, their thermo-mechanical behaviors and economic feasibility were analyzed using the long-term monitoring results. Although degradation of thermal performance and significant changes in the ground temperature were observed in the heating operation, it was concluded that the proposed design method could provide reliable design outcomes. The maximum thermal stress was estimated to be 2.38 MPa during the long-term monitoring, which is approximately 8.5% of the design strength criterion for cast-in-place concrete. Finally, compared with a conventional closed-loop vertical GHEX, the cast-in-place energy piles could reduce the initial investment cost by 25.31%, and the investment payback period was evaluated to be 1.61 years.

ACS Style

SangWoo Park; Seokjae Lee; Chihun Sung; Hangseok Choi. Applicability evaluation of cast-in-place energy piles based on two-year heating and cooling operation. Renewable and Sustainable Energy Reviews 2021, 143, 110906 .

AMA Style

SangWoo Park, Seokjae Lee, Chihun Sung, Hangseok Choi. Applicability evaluation of cast-in-place energy piles based on two-year heating and cooling operation. Renewable and Sustainable Energy Reviews. 2021; 143 ():110906.

Chicago/Turabian Style

SangWoo Park; Seokjae Lee; Chihun Sung; Hangseok Choi. 2021. "Applicability evaluation of cast-in-place energy piles based on two-year heating and cooling operation." Renewable and Sustainable Energy Reviews 143, no. : 110906.

Journal article
Published: 08 January 2021 in Energy and Buildings
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A coaxial-type ground heat exchanger (GHEX) is a closed-loop GHEX with heat exchange pipes in a borehole, arranged in a concentric tube-in-tube configuration. A coaxial-type GHEX enlarges the heat exchange area and induces turbulent flow more actively than conventional closed-loop GHEXs owing to the annular space formed by outer and inner pipes. Therefore, it improves the thermal performance of conventional GHEXs. Herein, the thermal performance of the coaxial-type GHEX was evaluated, and then compared with that of the closed-loop vertical GHEX. The Ground source heat pump (GSHP) system connected with the coaxial-type GHEXs was designed with the ground loop heat exchanger design program (i.e., GLHE-Pro). In accordance with the design, the GSHP system was constructed in a building basement, with four coaxial-type GHEXs and a closed-loop vertical GHEX for comparison purpose. Then, a series of field experiments (i.e., thermal response tests (TRTs), thermal performance tests (TPTs), short-term heating COP tests, and energy saving tests) were conducted to compare the thermal performance of the coaxial-type GHEXs and the closed-loop vertical GHEX with or without the GSHP system. As a result, the coaxial-type GHEX had 20% and 6.7% better thermal performance in TRT and TPT, respectively, than the closed-loop vertical GHEX. In addition, geothermal energy showed more stable performance with the coaxial-type GHEX in the GSHP system, than with the closed-loop vertical GHEX.

ACS Style

Seokjae Lee; SangWoo Park; Minkyu Kang; Hangseok Choi. Performance evaluation of coaxial-type GHEX in GSHP system installed in Korean residential building. Energy and Buildings 2021, 235, 110734 .

AMA Style

Seokjae Lee, SangWoo Park, Minkyu Kang, Hangseok Choi. Performance evaluation of coaxial-type GHEX in GSHP system installed in Korean residential building. Energy and Buildings. 2021; 235 ():110734.

Chicago/Turabian Style

Seokjae Lee; SangWoo Park; Minkyu Kang; Hangseok Choi. 2021. "Performance evaluation of coaxial-type GHEX in GSHP system installed in Korean residential building." Energy and Buildings 235, no. : 110734.

Journal article
Published: 06 January 2021 in Energy and Buildings
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Pile foundations support superstructures by transferring structural loads into the ground, where rocks or hard ground formations exist. Energy piles additionally utilize geothermal energy for heating and cooling buildings via embedded heat exchange pipes. However, when constructing energy piles, additional budgets are required for materials and labor to install conventional high-density polyethylene (HDPE) heat exchange pipes. The applicability of cast-in-place energy piles equipped with novel steel pipe heat exchangers (SPHXs) is investigated herein as substitutes for deformed rebars to reinforce concrete. Energy piles encasing SPHXs are expected to fulfill multiple functions of supporting structural loads and operating as heat exchangers without requiring additional heat exchange pipes. Two cast-in-place energy piles encasing SPHXs of different diameters were constructed in a test bed. Then, pile load tests (i.e., dynamic load test and lateral load test) were conducted to estimate the bearing capacities of these energy piles. Consequently, both energy piles secured safety factors greater than 2.0, and the allowable lateral loads were sufficient, indicating acceptable structural capacities as pile foundations. In addition, a thermal performance test (TPT) was performed on the selected energy pile, and the result was compared with that of a conventional cast-in-place energy pile to assess the heat exchange capacity of the energy pile with SPHXs. The thermal performance of the cast-in-place energy pile considered herein was 30% greater than that of the conventional energy pile of similar scale, which shows the applicability of the proposed energy piles.

ACS Style

Seokjae Lee; SangWoo Park; Dongkwan Kim; Dongwook Ahn; Hangseok Choi. Dual performance of novel steel pipe heat exchangers equipped in cast-in-place energy pile. Energy and Buildings 2021, 234, 110725 .

AMA Style

Seokjae Lee, SangWoo Park, Dongkwan Kim, Dongwook Ahn, Hangseok Choi. Dual performance of novel steel pipe heat exchangers equipped in cast-in-place energy pile. Energy and Buildings. 2021; 234 ():110725.

Chicago/Turabian Style

Seokjae Lee; SangWoo Park; Dongkwan Kim; Dongwook Ahn; Hangseok Choi. 2021. "Dual performance of novel steel pipe heat exchangers equipped in cast-in-place energy pile." Energy and Buildings 234, no. : 110725.

Journal article
Published: 22 September 2020 in Computers and Geotechnics
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A stepwise discrete element-finite element (DE/FE) combined numerical framework was proposed for efficiently estimating the effective thermal conductivity of spherical particulate media, which considers the thermal interaction of particle-to-particle and particle-to-pore filling material. The particulate composition was numerically modeled by the discrete element method (DEM), which was followed by a series of heat-transfer analyses formulated in the finite element method (FEM). In order to overcome difficulty of generating meshes in the FE modeling, a novel particle-size-reduction method was developed in the course of the mesh generation. The effective thermal conductivity of glass-bead specimens was measured at the porosity of 0.32, 0.35 and 0.38 under saturated and saturated-frozen conditions. The numerical framework resulted in the accurate estimation of effective thermal conductivity of glass-bead specimens in comparison with the laboratory measurements with the errors less than 5%. In addition, to verify the applicability of the proposed numerical framework to actual geologic materials, the effective thermal conductivity of Jumunjin standard sand specimens was considered at the porosity of 0.41, 0.43 and 0.45 under saturated and saturated-frozen conditions. The estimation errors in the numerical framework for the Jumunjin standard sand were less than 3%, which reveals the applicability of the proposed method.

ACS Style

Dongseop Lee; Khanh Pham; Minkyu Kang; Sangyeong Park; Hangseok Choi. Stepwise DE/FE combined approach for estimating effective thermal conductivity of frozen spherical particulate media. Computers and Geotechnics 2020, 128, 103837 .

AMA Style

Dongseop Lee, Khanh Pham, Minkyu Kang, Sangyeong Park, Hangseok Choi. Stepwise DE/FE combined approach for estimating effective thermal conductivity of frozen spherical particulate media. Computers and Geotechnics. 2020; 128 ():103837.

Chicago/Turabian Style

Dongseop Lee; Khanh Pham; Minkyu Kang; Sangyeong Park; Hangseok Choi. 2020. "Stepwise DE/FE combined approach for estimating effective thermal conductivity of frozen spherical particulate media." Computers and Geotechnics 128, no. : 103837.

Tunnel engineering
Published: 10 September 2020 in KSCE Journal of Civil Engineering
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The artificial ground freezing (AGF) method has been used in many geotechnical engineering applications such as temporary excavation support, underpinning and groundwater cutoff. The AGF method utilizes a refrigerant such as liquid nitrogen or brine, circulating through embedded freezing pipes in order to freeze the ground. In this paper, two in-situ cryogenic freezing experiments (i.e., single freezing-pipe test and frozen-wall formation test) were performed using liquid nitrogen to simulate the AGF in a Korean marine clay deposit, in which the freezing rate was evaluated. The thermal conductivity of frozen and unfrozen marine clay was evaluated by performing typical laboratory experiments. In addition, the strength and stiffness of frozen-thawed deposits were comparatively measured by sounding tests (i.e., piezocone penetration test and lateral loading test). The freezing rate of the frozen-wall formation test in the Korean marine clay deposit was approximately twice as high as that of the single freezing pipe test. Compared to the original marine clay deposit, the frozen-thawed marine clay showed a significant reduction in strength and stiffness.

ACS Style

Hyun-Jun Choi; Dongseop Lee; Jongmuk Won; Hyobum Lee; Hangseok Choi. Influence of In-situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay. KSCE Journal of Civil Engineering 2020, 1 -15.

AMA Style

Hyun-Jun Choi, Dongseop Lee, Jongmuk Won, Hyobum Lee, Hangseok Choi. Influence of In-situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay. KSCE Journal of Civil Engineering. 2020; ():1-15.

Chicago/Turabian Style

Hyun-Jun Choi; Dongseop Lee; Jongmuk Won; Hyobum Lee; Hangseok Choi. 2020. "Influence of In-situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay." KSCE Journal of Civil Engineering , no. : 1-15.

Journal article
Published: 09 September 2020 in CATENA
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In this study, ensemble learning was applied to develop a classification model capable of accurately estimating slope stability. Two prominent ensemble techniques—parallel learning and sequential learning—were applied to implement the ensemble classifiers. Additionally, for comparison, eight versatile machine learning algorithms were utilized to formulate the single-learning classification models. These classification models were trained and evaluated on the well-established global database of slope documented from 1930 to 2005. The performance of these classification models was measured by considering the F1 score, accuracy, receiver operating characteristic (ROC) curve and area under the ROC curve (AUC). Furthermore, K-fold cross-validation was employed to fairly assess the generalization capacity of these models. The obtained results demonstrated the advantage of ensemble classifiers over single-learning classification models. When ensemble learning was used instead of the single learning, the average F1 score, accuracy, and AUC of the models increased by 2.17%, 1.66%, and 6.27%, respectively. In particular, the ensemble classifiers with sequential learning exhibited better performance than those with parallel learning. The ensemble classifiers on the extreme gradient boosting (XGB-CM) framework clearly provided the best performance on the test set, with the highest F1 score, accuracy, and AUC of 0.914, 0.903, and 0.95, respectively. The excellent performance on the spatially well-distributed database along with its capacity to distribute computing indicates the significant potential applicability of the presented ensemble classifiers, particularly the XGB-CM, for landslide risk assessment and management on a global scale.

ACS Style

Khanh Pham; Dongku Kim; Sangyeong Park; Hangseok Choi. Ensemble learning-based classification models for slope stability analysis. CATENA 2020, 196, 104886 .

AMA Style

Khanh Pham, Dongku Kim, Sangyeong Park, Hangseok Choi. Ensemble learning-based classification models for slope stability analysis. CATENA. 2020; 196 ():104886.

Chicago/Turabian Style

Khanh Pham; Dongku Kim; Sangyeong Park; Hangseok Choi. 2020. "Ensemble learning-based classification models for slope stability analysis." CATENA 196, no. : 104886.

Short communication
Published: 16 January 2020 in Ocean Engineering
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The application of vertical drains along with preloading to accelerate the consolidation rate of dredged soil has been widely used. However, the conventional analytical or numerical models cannot predict the nonlinear finite-strain consolidation behavior of dredge-soil deposits accurately because the vertical drains are installed in the middle of a self-weight-consolidation process. This paper establishes a mathematical and numerical model for a 2-D axisymmetric nonlinear finite-strain consolidation, for which the self-weight consolidation and the radial drainage through vertical drains are considered. Besides, a series of lab-scale self-weight-consolidation tests were conducted, which can simulate the vertical-drain installation. Experimental results along with those of the simplified method (Lee et al., 2016) were then utilized to verify performance of the proposed model. The results demonstrate that the proposed model appropriately predicts the nonlinear finite-strain self-weight consolidation behavior of dredged soils, and its application with vertical drains is suitable for designing dredged-soil improvement. Moreover, the most important advantage of the proposed model is to optimize the schedule of dredging/landfilling construction.

ACS Style

Hyobum Lee; Taehoon Kwak; Dongku Kim; Hangseok Choi. Consideration of radial flow in nonlinear finite-strain self-weight consolidation of dredged soil. Ocean Engineering 2020, 197, 106889 .

AMA Style

Hyobum Lee, Taehoon Kwak, Dongku Kim, Hangseok Choi. Consideration of radial flow in nonlinear finite-strain self-weight consolidation of dredged soil. Ocean Engineering. 2020; 197 ():106889.

Chicago/Turabian Style

Hyobum Lee; Taehoon Kwak; Dongku Kim; Hangseok Choi. 2020. "Consideration of radial flow in nonlinear finite-strain self-weight consolidation of dredged soil." Ocean Engineering 197, no. : 106889.

Journal article
Published: 02 July 2019 in Energy and Buildings
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In general, the design of closed-loop vertical ground heat exchangers (GHEXs) is to determine the required borehole length for providing the heating and cooling load of a target building. However, the same design procedure cannot be applied to the cast-in-place energy pile since the configuration of the heat exchange pipe inside the pile is too varied and the size of the borehole is relatively large. In this paper, the effect of configuration and denseness of heat exchange pipe inside the energy pile was experimentally and numerically evaluated comparing with conventional GHEXs. First, field experiments were performed for six cast-in-place energy piles constructed in a test bed. The results showed that the cast-in-place energy piles could provide higher thermal performance per unit borehole length than the other conventional types of GHEXs by increasing the heat exchange area along with much longer heat exchange pipes. However, the over-tight layout might diminish the improvement of thermal performance due to thermal interference between each pipe loop. In addition, the long-term thermal behavior of energy piles and changes in ground temperature were estimated with numerical simulations. With the simulation results, a design chart was provided for evaluating the effect of thermal interference on energy pile performance.

ACS Style

SangWoo Park; Seokjae Lee; Dongseop Lee; Dongwook Ahn; Hangseok Choi. Effect of thermal interference on energy piles considering various configurations of heat exchangers. Energy and Buildings 2019, 199, 381 -401.

AMA Style

SangWoo Park, Seokjae Lee, Dongseop Lee, Dongwook Ahn, Hangseok Choi. Effect of thermal interference on energy piles considering various configurations of heat exchangers. Energy and Buildings. 2019; 199 ():381-401.

Chicago/Turabian Style

SangWoo Park; Seokjae Lee; Dongseop Lee; Dongwook Ahn; Hangseok Choi. 2019. "Effect of thermal interference on energy piles considering various configurations of heat exchangers." Energy and Buildings 199, no. : 381-401.

Journal article
Published: 23 May 2019 in Geoderma
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Approximate estimates employing the pedotransfer function (PTF) for predicting the soil-water characteristic curve have received general agreement among the geotechnical engineering society. Notably, the machine-learning-based PTFs (ML-PTFs) offer robust approaches with high prediction accuracy. This study analyzed the potential factors governing the prediction accuracy of the neural-network-based PTF (NN-PTF), which is one of the most popular ML-PTFs. Multiple analysis scenarios for the NN structure, learning algorithm and data processing were presented to evaluate the influence of these components. The analyses were performed on the UNsaturated Soil hydraulic DAtabase, which consists of a broad range of soil types. It is noted that employing the Bayesian regularization significantly improved the prediction accuracy for the same NN structure and optimizing algorithm when compared to using the early stopping, i.e., the maximum reduction in root mean squared error (RMSE) was 0.014. Architectural selection of the network worked most efficiently in case of the Bayesian regularization neural network (BRNN), i.e., RMSE dropped by 36% when the number of neurons increased from 9 to 54. Contrarily, an insignificant variation of RMSE indicated that increasing the NN complexity did not affect the performance of NN-PTF with the conjugate gradient descent and the early stopping. In addition, training the NN-PTF with a well-processed dataset could improve the prediction accuracy, i.e., the maximum reduction in RMSE was 0.004. Overall, the three-hidden-layer BRNN trained by the processed dataset outperformed the other scenarios in consideration, with RMSE = 0.028 and R2 = 0.977. Consequently, the data pre-processing and Bayesian regularization are strongly suggested for deriving the NN-PTF.

ACS Style

Khanh Pham; Dongku Kim; Yuemyung Yoon; Hangseok Choi. Analysis of neural network based pedotransfer function for predicting soil water characteristic curve. Geoderma 2019, 351, 92 -102.

AMA Style

Khanh Pham, Dongku Kim, Yuemyung Yoon, Hangseok Choi. Analysis of neural network based pedotransfer function for predicting soil water characteristic curve. Geoderma. 2019; 351 ():92-102.

Chicago/Turabian Style

Khanh Pham; Dongku Kim; Yuemyung Yoon; Hangseok Choi. 2019. "Analysis of neural network based pedotransfer function for predicting soil water characteristic curve." Geoderma 351, no. : 92-102.

Journal article
Published: 05 March 2019 in Applied Sciences
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The presence of retained colloidal particles causes the retardation of contaminant transport when the contaminant is favorably adsorbed to colloidal particles. Although the particle size distribution affects the retention behavior of colloidal particles, the impact of particle size distribution on contaminant transport has not been reported to date. This study investigates the impact of the particle size distribution of the colloidal particles on contaminant transport through numerical simulation by representing the particle size distribution as a lognormal distribution function. In addition, the bed efficiency and contaminant saturation of simulated breakthrough curves were calculated, and a contaminant transport model with the Langmuir isotherm for the reaction between the contaminant–sand and contaminant–colloidal particle was introduced and validated with experimental data. The simulated breakthrough curves, bed efficiency, and contaminant saturation indicated that an increase in the mean and standard deviation of the particle size distribution causes the retardation of contaminant transport.

ACS Style

Jongmuk Won; Dongseop Lee; Khanh Pham; Hyobum Lee; Hangseok Choi. Impact of Particle Size Distribution of Colloidal Particles on Contaminant Transport in Porous Media. Applied Sciences 2019, 9, 932 .

AMA Style

Jongmuk Won, Dongseop Lee, Khanh Pham, Hyobum Lee, Hangseok Choi. Impact of Particle Size Distribution of Colloidal Particles on Contaminant Transport in Porous Media. Applied Sciences. 2019; 9 (5):932.

Chicago/Turabian Style

Jongmuk Won; Dongseop Lee; Khanh Pham; Hyobum Lee; Hangseok Choi. 2019. "Impact of Particle Size Distribution of Colloidal Particles on Contaminant Transport in Porous Media." Applied Sciences 9, no. 5: 932.

Journal article
Published: 01 January 2019 in Vadose Zone Journal
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This study performed a series of experiments to examine the hydraulic-mechanical properties of granite-weathered residual soil in the Korean Peninsula. Particular attention was paid to the soil-water characteristic curve (SWCC) and shear strength under various stress states and matric suction levels. The experimental results indicated the decisive influence of the stress state on the SWCC, notably in the low range of matric suction. In addition, the evolution of shear strength with suction became significant under high net confining stress. The effective stress using the stress-independent SWCC could not describe the actual mechanical behaviors of the unsaturated soil. The relevant effective stress for the granite-weathered residual soil in consideration was then proposed. Next, a numerical framework for strength analysis with infiltration was developed to manifest the practical applications of the experimental results. The analysis results revealed the potential failure mechanisms of the geotechnical infrastructures induced by rainfall. Ignoring the contribution of matric suction may lead to overly conservative outcomes and cannot capture the realistic performance of soil under the rainfall condition. Moreover, the stress-dependent hydraulic properties are suggested for application in strength analysis for the safer design of geotechnical infrastructure. Copyright © 2019. . © 2019 The Author(s).

ACS Style

Khanh Pham; Dongku Kim; In-Mo Lee; Hangseok Choi. Hydraulic‐Mechanical Properties of Unsaturated Granite‐Weathered Residual Soil in Korea. Vadose Zone Journal 2019, 18, 1 -13.

AMA Style

Khanh Pham, Dongku Kim, In-Mo Lee, Hangseok Choi. Hydraulic‐Mechanical Properties of Unsaturated Granite‐Weathered Residual Soil in Korea. Vadose Zone Journal. 2019; 18 (1):1-13.

Chicago/Turabian Style

Khanh Pham; Dongku Kim; In-Mo Lee; Hangseok Choi. 2019. "Hydraulic‐Mechanical Properties of Unsaturated Granite‐Weathered Residual Soil in Korea." Vadose Zone Journal 18, no. 1: 1-13.

Journal article
Published: 10 November 2018 in Applied Sciences
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The energy slab is a novel type of horizontal Ground Heat Exchanger (GHEX), where heat exchange pipes are encased in building slab structures. The thermal performance of energy slabs is usually inferior to the conventional closed-loop vertical GHEX because its installation depth is relatively shallow and therefore affected by ambient air temperature. In this paper, heat exchange pipes were made of not only conventional high-density polyethylene (HDPE), but also stainless steel (STS), which is expected to enhance the thermal performance of the energy slabs. In addition to a floor slab, a side wall slab was also used as a component of energy slabs to maximize the use of geothermal energy that can be generated from the underground space. Moreover, a thermal insulation layer in the energy slabs was considered in order to reduce thermal interference induced by ambient air temperature. Consequently, two different field-scale energy slabs (i.e., floor-type and wall-type energy slabs) were constructed in a test bed, and two types of heat exchange pipes (i.e., STS pipe and HDPE pipes) were installed in each energy slab. A series of thermal response tests (TRTs) and thermal performance tests (TPTs) were conducted to evaluate the heat exchange performance of the constructed energy slabs. Use of the STS heat exchange pipe enhanced the thermal performance of energy slabs. Additionally, the wall-type energy slab had a similar thermal performance to the floor-type energy slab, which infers the applicability of the additional use of the wall-type energy slab. Note that if an energy slab is not thermally cut off from the building’s interior space with the aid of thermal insulation layers, heat exchange within the energy slabs should be significantly influenced by fluctuations in ambient temperature.

ACS Style

Seokjae Lee; SangWoo Park; Minkyu Kang; Hangseok Choi. Field Experiments to Evaluate Thermal Performance of Energy Slabs with Different Installation Conditions. Applied Sciences 2018, 8, 2214 .

AMA Style

Seokjae Lee, SangWoo Park, Minkyu Kang, Hangseok Choi. Field Experiments to Evaluate Thermal Performance of Energy Slabs with Different Installation Conditions. Applied Sciences. 2018; 8 (11):2214.

Chicago/Turabian Style

Seokjae Lee; SangWoo Park; Minkyu Kang; Hangseok Choi. 2018. "Field Experiments to Evaluate Thermal Performance of Energy Slabs with Different Installation Conditions." Applied Sciences 8, no. 11: 2214.

Journal article
Published: 22 October 2018 in Renewable Energy
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The coaxial-type Ground Heat Exchanger (GHEX) possesses a concentric tube-in-tube configuration, which can provide a sufficient heat exchange area, and induces turbulent flow conditions. Therefore, the coaxial-type GHEX is expected to outperform the conventional U-type GHEX in terms of thermal performance. However, it is very important to design an optimal configuration (i.e., pipe length, the roughness of pipe wall and the shape of cross section) for the coaxial-type GHEX to generate turbulent flow inside the pipe and to achieve sufficient heat exchange area. In this paper, GHEXs of various construction conditions were considered, and the factors governing the thermal performance of coaxial-type GHEX were identified through field tests. Four 50-m-deep coaxial-type GHEXs were constructed in a test bed with different pipe materials, pipe diameters and grouting materials. In addition, a 50-m-deep closed-loop vertical GHEX was separately constructed to compare the thermal performance with the coaxial-type GHEXs. A series of in-situ thermal response test (TRT) and in-situ thermal performance test (TPT) was performed in the constructed coaxial-type GHEXs to investigate the effect of various construction conditions on thermal performance. As a result, the thermal performance of coaxial-type GHEXs is directly influenced by the thermal conductivity of the pipe and grouting material. The pipe diameter also influences the thermal performance of coaxial-type GHEX. Especially, it is noted that an optimal flow rate exists, which maximizes the thermal performance of the coaxial-type GHEX.

ACS Style

Kwanggeun Oh; Seokjae Lee; SangWoo Park; Shin-In Han; Hangseok Choi. Field experiment on heat exchange performance of various coaxial-type ground heat exchangers considering construction conditions. Renewable Energy 2018, 144, 84 -96.

AMA Style

Kwanggeun Oh, Seokjae Lee, SangWoo Park, Shin-In Han, Hangseok Choi. Field experiment on heat exchange performance of various coaxial-type ground heat exchangers considering construction conditions. Renewable Energy. 2018; 144 ():84-96.

Chicago/Turabian Style

Kwanggeun Oh; Seokjae Lee; SangWoo Park; Shin-In Han; Hangseok Choi. 2018. "Field experiment on heat exchange performance of various coaxial-type ground heat exchangers considering construction conditions." Renewable Energy 144, no. : 84-96.

Journal article
Published: 01 September 2018 in Engineering Geology
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This paper presents a simple numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions. The advantage of the proposed framework, from the practical point of view, is to predict the variability in stability of partially saturated slope along with rainfall data. Moreover, the presented framework is adaptable to different types of soil-water characteristic curve (SWCC) models, hydraulic boundary conditions, and heterogeneity in soil properties. A series of stability analyses for hypothetical hillslopes under various conditions was performed to scrutinize the potential failure mechanisms induced by rainfall. The examined factors include the soil texture, rainfall intensity, heterogeneity in soil properties and hydraulic boundary conditions. Also, four widely used SWCC models were applied to assess the influence of this component. The SWCC model was demonstrated to strongly dominate the results of the infinite slope stability analysis under transient unsaturated seepage conditions. For homogeneous hillslopes with a fixed water table, when the rainfall intensity (q) equals the saturated hydraulic conductivity (Ks), slope failure was expected to occur after a short time of rainfall with a relatively shallow slip depth. In contrast, for heterogeneous hillslopes or hillslopes with impermeable bedrock, the failure could take place when q is less than Ks, and the potential failure surface was close to the discontinuity interface or at the bottom of the hillslope. Finally, three case studies of landslides documented in literature were utilized to demonstrate the predictability of the proposed framework in practical applications.

ACS Style

Khanh Pham; Dongku Kim; Hyun-Jun Choi; In-Mo Lee; Hangseok Choi. A numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions. Engineering Geology 2018, 243, 36 -49.

AMA Style

Khanh Pham, Dongku Kim, Hyun-Jun Choi, In-Mo Lee, Hangseok Choi. A numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions. Engineering Geology. 2018; 243 ():36-49.

Chicago/Turabian Style

Khanh Pham; Dongku Kim; Hyun-Jun Choi; In-Mo Lee; Hangseok Choi. 2018. "A numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions." Engineering Geology 243, no. : 36-49.