• Computers and Concrete
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• v.34 no.2
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• pp.151-168
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• 2024

This research aimed to appraise the effectiveness of four optimization approaches - cuckoo optimization algorithm (COA), multi-verse optimization (MVO), particle swarm optimization (PSO), and teaching-learning-based optimization (TLBO) - that were enhanced with an artificial neural network (ANN) in predicting the bearing capacity of shallow foundations located on cohesionless soils. The study utilized a database of 97 laboratory experiments, with 68 experiments for training data sets and 29 for testing data sets. The ANN algorithms were optimized by adjusting various variables, such as population size and number of neurons in each hidden layer, through trial-and-error techniques. Input parameters used for analysis included width, depth, geometry, unit weight, and angle of shearing resistance. After performing sensitivity analysis, it was determined that the optimized architecture for the ANN structure was 5×5×1. The study found that all four models demonstrated exceptional prediction performance: COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP. It is worth noting that the MVO-MLP model exhibited superior accuracy in generating network outputs for predicting measured values compared to the other models. The training data sets showed R² and RMSE values of (0.07184 and 0.9819), (0.04536 and 0.9928), (0.09194 and 0.9702), and (0.04714 and 0.9923) for COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP methods respectively. Similarly, the testing data sets produced R² and RMSE values of (0.08126 and 0.07218), (0.07218 and 0.9814), (0.10827 and 0.95764), and (0.09886 and 0.96481) for COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP methods respectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.95-102
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• 2014

In this paper, a coupling scheme for applying finite element analysis(FEA) programs, such as, LS-DYNA and MIDAS/Civil, to a nonlinear soil structure interaction analysis by the boundary reaction method(BRM) is presented. With the FEA programs, the structure and soil media are discretized by linear or nonlinear finite elements. To absorb the outgoing elastic waves to unbounded soil region as much as possible, the PML elements and viscous-spring elements are used at the outer FE boundary, in the LS-DYNA model and in MIDAS/Civil model, respectively. It is also assumed that all the nonlinear elements in the problem are limited to structural region. In this study, the boundary reaction forces for the use in the BRM are calculated using the KIESSI-3D program by solving soil-foundation interaction problem subjected to incident seismic waves. The effectiveness of the proposed approach is demonstrated with a linear SSI seismic analysis problem by comparing the BRM solution with the conventional SSI solution. Numerical comparison indicates that the BRM can effectively be applied to a nonlinear soil-structure analysis if motions at the foundation obtained by the BRM for a linear SSI problem excluding the nonlinear structure is conservative.

• Journal of the Korean Geotechnical Society
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• v.36 no.7
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• pp.5-14
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• 2020

Kansai International Airport (KIX) was opened in September 1994. Although 26 years have passed since the completion of the first island, long-term settlement is still in progress. This settlement occurs in the Pleistocene layer. For it is not easy to determine the permeability of the Pleistocene sand layer because the thickness and the degree of fine content in the horizontal direction are constantly changing. In addition, it is also a difficult to predict the interactive behavior of the ground due to the construction of the second phase island adjacent to it. In order to solve this problem, a two-dimensional finite element analysis considering elasto-viscoplastic was performed to evaluate the long-term deformation, including the interactive behavior of the alternating Pleistocene foundation due to the construction of two adjacent reclaimed islands. In general, two-dimensional analysis can be used when a section can represent the entire sections. However, Kansai Airport is an artificial reclaimed island so two-dimensional analysis cannot solve the problem such as the stress deformation in the corners of the island. Additionally, the structure of the actual sub-ground through physical exploration is non-homogeneity and its thickness is also not constant. Therefore, there are limitations for the two-dimensional analysis to explain the phenomena. That is, three-dimensional analysis is strongly required. Due to these demands, the author extended the existing two-dimensional program capable of elasto-viscoplastic analysis to three-dimensional and completed the verification of the three-dimensional program developed through one-dimensional consolidation analysis. In order to demonstrate the validity of the developed 3D program that has been verified, an analysis is performed under the same analysis conditions as the existing research using a two-dimensional program. The effectiveness of the developed 3D numerical analysis program was demonstrated by comparing the analysis results with the 2D results and actual measurement data.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.537-543
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• 2008

To effectively delineate the foundation of stone relics by GPR and seismic refraction methods, a geological engineering model was constructed with alternating layer of soil and gravel to a depth of 3 m. This study was aimed at mapping the boundaries of model ground structure and interfaces of alternating layer using the various frequency antenna in GPR survey and seismic velocities. Compared to the resolution from the high frequency antenna, the image resolution from the survey using 100 Hz antenna is the lower, but with the deeper image coverage. On the contrast, the deeper structure was not mapped in the higher frequency data due to higher absorption effect, but the shallow layered zone was distinctively resolved. Therefore subsurface images were effectively provided by integrating the data with 100 MHz and 450 MHz antennas for the deep and shallow structures, respectively. Regarding the seismic refraction data, the boundaries of the model and interface of the alternating layers were not successfully mapped due to the limit of the survey length. However, the equivalent contours of low velocity extended deep as considerable velocity contrasts with surrounding ground.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.149-161
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• 2022

This study selected the indexes for evaluating the damage of the railway embankments due to liquefaction from the earthquake damage cases of railway embankments. The study correlated the selected indexes and the settlement of the embankment crest from the dynamic numerical analysis. Further, the correlation was used to develop a method for evaluating the liquefaction damage to the railway embankment. The damage cases and damage types were analyzed, and referring to the liquefaction damage assessment method for other structures, the embankment height (H), the non-liquefiable layer thickness (H₁), and the liquefaction potential index were selected as indexes for evaluating the damage. The study performed dynamic effective stress analyses on the railway embankment, and the PM4-Sand model was applied as the constitutive liquefaction model for the embankment foundation ground. The model's validity was first verified by comparing it with the existing dynamic centrifugal model test results performed on the railway embankment. Nine sites where the foundation ground can be liquefied were selected from the data of 549 embankments of the Honam High-speed Railway in Korea. Further, dynamic numerical analyses using four seismic waves as input earthquake load were performed for the selected site sections. The numerical analysis results confirmed the correlation between the evaluation indexes and the embankment crest settlement. A method for efficiently evaluating the damage to the embankment due to liquefaction was proposed using the chart obtained from this correlation.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.273-286
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• 2019

A derelict bridge called WoljungGyo was restored in Gyeongju, the capital city of ancient Silla. WoljungGyo was originally built in 760AD, and later rebuilt in 1280AD during the Goryeo Kingdom. The bridge lasted in working condition for at least 520 years. The bridge was uncovered to the remains of both abutments and four piers, with only one or two steps remaining. One of the foundation for piers showed evidence of partial settlement. The cause of the partial settlement is important for the successful restoration of the bridge so that an extensive investigation was carried out, which includes layer stratification by boring, 2-D stiffness profiling by surface-wave tests, and large scaled-plate load test for evaluating capacity. In addition to the field studies in the Woljunggyo bridge, 3-D finite element analysis was also conducted. Based on the results of the site investigation and the numerical analysis, it was concluded that the further ground improvement to build the piers was not necessary so that the gravels were placed and leveled underneath the existing pier stones to compensate partial settlement before the restoration.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.29-40
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• 2023

In this study, we investigated the reinforcing effects of waveform micropiles in a stratigraphic setting comprising buried soil, weathered soil, and weathered rock. We conducted a series of field load tests and determined that waveform micropiles exhibited sufficient bearing capacity through frictional resistance in the soil layer and demonstrated favorable constructability in conditions with deep bedrock layers. Moreover, the vertical stiffness of waveform micropiles was approximately 2.2 times higher than that of conventional micropiles when subjected to the same design load. Pile group load tests comprising conventional and waveform micropiles showed that micropiles with higher stiffness carried a greater proportion of the load. Although there was no significant difference in the bearing capacity between conventional and waveform micropiles under the same design load, waveform micropiles with higher stiffness showed a load-carrying capacity 1.7 to 3.2 times greater than that of conventional micropiles. These findings suggest that waveform micropiles can be effectively used for foundation reinforcement and reduce the risk of foundation failure when increased loads due to modifications such as expansion remodeling are expected.

• Journal of the Korean Institute of Landscape Architecture
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• v.43 no.4
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• pp.62-74
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• 2015

This study was carried out to provide examples of planting methods for the construction of street green spaces with abundant greenery by analyzing road type, surrounding land use and planting structures in street green spaces on Port Island, Kobe, Japan. Port Island_(total area: 826ha) is a marine cultural city located in Japan's first artificial island with facilities of urban function and port facilities. The study site was designated at 11 plots of $55{\sim}285m^2$ on Port Island, and topography structure styles were divided into four types with mounding style, slope style, slope and flat style, flat style according to the adjacent roads width. The area adjacent to the middle roads with high levels of noise and pollution set up the mounding style, slope style, slope and flat style of multi-layer structures using topographic properties. The area adjacent to small roads focused on a green strip with shrubs on a flat style. Surrounding land-uses include a public institution, housing complex, and a commercial building. The planting concept was a buffer and landspace function in case of the middle road_(lane 4) while the small road_(lane 2) was a landspace function. Planting species were diverse with Liquidambe formosana, Cinnamomum camphora, Sapium sebiferum, Cedrela sinensis, Laeocarpus sylvestris var. ellipticus, Ginkgo biloba, Prunus serrulata var. spontanea, Zelkova serrata, Quercus glauca, Juniperus chinensis, Magnolia kobus, Rhododendron spp., Camellia japonica, Abelia mosanensis, etc. Planting density was 0.02~0.08(0.04) individual/$m^2$ at the canopy layer, 0.02~0.08(0.04) individual/$m^2$ at the understory layer. Ratio of green coverage was 40.0~173.7(93.0)% at the canopy layer, 2.1~79.8(34.9)% at the understory layer and 17.9~64.2(32.9)% at the shrub layer. $Gr{\ddot{u}}volumenzahl$ was $1.43{\sim}6.67(4.13)m^3/m^2$ at the canopy layer, $0.02{\sim}2.01(0.85)m^3/m^2$ at the understory layer and $0.14{\sim}0.58(0.26)m^3/m^2$ at the shrub layer. The ratio of green coverage of street green space on Port Island was higher than that of Seoul, and particularly, the ratio of green coverage and $gr{\ddot{u}}volumenzahl$ at the shrub layer differed, compared to the main street green space in Korea. The result of this study may be applicable to other coastal reclaimed cities in terms of setting methods for street greenery considering the topography structure, planting structure and planting function.

• Applied Microscopy
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• v.39 no.4
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• pp.349-354
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• 2009

In this paper we have constructed three dimensional images and examined structural failure on thin film transistor (TFT) liquid crystal display (LCD) by using dual-beam focused ion beam (FIB) and IMOD software. Specimen was sectioned with dual-beam focused ion beam. Series of two dimensional images were obtained by scanning electron microscopy. Three dimensional reconstruction was constructed from them by using IMOD software. The short defect between Gate layer and Data layer was found from the result of three dimensional reconstruction. That phenomena made the function of the gate lost and data signal supplied to the electrode though the Drain continuously. That signal made continuous line defect. The result of the three dimensional reconstruction, serial section, SEM imaging by using the FIB will be the foundation of the next advanced study.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.1015-1020
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• 2012

Resistance of the front electrode is the highest proportion of the ingredients of the series resistance in crystalline silicon solar cell. While resistance of the front electrode is decreased with larger area, it induces the optical loss, causing the conversion efficiency drop. Therefore the front electrode with high aspect ratio increasing its height and decreasing is necessary for high-efficiency solar cell in considering shadowing loss and resistance of front electrode. In this paper, we used the screen printing method to form high aspect ratio electrode by multiple printing. Screen printing is the straightforward technology to establish the electrodes in silicon solar cell fabrication. The several printed front electrodes with Ag paste on silicon wafer showed the significantly increased height and slightly widen finger. As a result, the resistance of the front electrode was decreased with multiple printing even if it slightly increased the shadowing loss. We showed the improved electrical characteristics for c-Si solar cell with repeatedly printed front electrode by 0.5%. It lays a foundation for high efficiency solar cell with high aspect ratio electrode using screen printing.