• Geomechanics and Engineering
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• v.22 no.4
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• pp.291-303
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• 2020

The deformation of the rock surrounding a tunnel manifests due to the stress redistribution within the surrounding rock. By observing the deformation of the surrounding rock, we can not only determine the stability of the surrounding rock and supporting structure but also predict the future state of the surrounding rock. In this paper, we used grey system theory to analyse the factors that affect the deformation of the rock surrounding a tunnel. The results show that the 5 main influencing factors are longitudinal wave velocity, tunnel burial depth, groundwater development, surrounding rock support type and construction management level. Furthermore, we used seismic prospecting data, preliminary survey data and excavated section monitoring data to establish a neural network learning model to predict the total amount of deformation of the surrounding rock during tunnel collapse. Subsequently, the probability of a change in deformation in each predicted section was obtained by using a Bayesian method for detecting change points. Finally, through an analysis of the distribution of the change probability and a comparison with the actual situation, we deduced the survey mark at which collapse would most likely occur. Surface collapse suddenly occurred when the tunnel was excavated to this predicted distance. This work further proved that the Bayesian method can accurately detect change points for risk evaluation, enhancing the accuracy of tunnel collapse forecasting. This research provides a reference and a guide for future research on the probability analysis of tunnel collapse.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.1
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• pp.62-66
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• 2017

The interest on the potential earthquake magnitude and the request on the earthquake-resistant design examination for coastal structures are emerged because of the recently occurred magnitude 5.8 earthquake in Gyeoung-Ju, Korea. In this study, the magnitude and its confidence intervals with the return periods are estimated using the KMA earthquake magnitude data (over 3.5 and 4.0 in magnitude) by the non-parametric extreme value analysis. In case of using the "over 4.0" data set, the estimated magnitudes on the 50- and 100-years return periods are 5.81 and 5.94, respectively. Their 90% confidence intervals are estimated to be 5.52-6.11, 5.62-6.29, respectively. Even though the estimated magnitudes have limitations not considering the spatial distribution, it can be used to check the stability of the diverse coastal structures in the perspective of the life design because the potential magnitude and its confidence intervals in Korea are estimated based on the available 38-years data by the extreme value analysis.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.1
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• pp.17-27
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• 2004

A new earthquake design method performing iterative calculations using secant stiffness was developed. The proposed design method has the advantages of convenience and stability in numerical analysis because it uses elastic analysis. At the same time, the proposed design method can accurately estimate the strength and ductility demands on the members because it performs the analysis on the inelastic behavior of structure using iterative calculation. In the present study, the procedure of the proposed design method was established, and a computer program incorporating the proposed method was developed. Design examples using the proposed method were presented, and its advantages were presented by the comparisons with existing design methods using elastic or inelastic analysis. The proposed design method, as an integrated method of analysis and design, can address the earthquake design strategy devised by the engineer. such as ductility limit on each member, the design concept of strong column - weak beam, and etc. In addition, through iterative calculations on the structure preliminarily designed only with member sizing, the strength and ductility demands of each member can be directly calculated so as to satisfy the given design strategy. As the result. economical and safe design can be achieved.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.5
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• pp.23-29
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• 2008

This study investigates the dynamic instability of strength-limited bilinear single degree of freedom (SDF) systems under seismic excitation. The strength-limited bilinear hysteretic model best replicates the hysteretic behavior of the steel moment resisting frames. To estimate the dynamic instability of SDF systems, the collapse strength ratio is used, which is the yield-strength reduction factor when collapse occurs. Statistical studies are carried out to estimate median collapse strength ratios and those dispersions of strength-limited bilinear SDF systems with given natural periods, hardening stiffness ratios, post-capping stiffness ratios, ductility and damping ratios ranging from 2 to 20% subjected to 240 earthquake ground motions recorded on stiff soil sites. Equations to calculate median and standard deviation of collapse strength ratios in strength-limited bilinear SDF systems are obtained through nonlinear regression analysis. By using the proposed equations, this study estimated the probabilistic distribution of collapse strength ratios, and compared this with the exact values from which the accuracy of the proposed equations was verified.

• Tunnel and Underground Space
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• v.12 no.2
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• pp.120-129
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• 2002

Natural cavitied were found at shallow depth during construction of a huge bridge in Cambro-Ordovician Limestone Basin in the central part or Korea. The distribution patterns of cavities in this area were investigated carefully with a supplementary field job such as a structural geological survey, a geophysical survey, and a rock mechanical test in laboratory or field. A structural geological mapping produced a detail geological map focusing the route of the Proposed highway. It suggested that there were three faults in this wet and these faults had an influence on the mechanism of natural cavities. Among many kinds of geophysical surveys, an electrical resistivity prospecting was applied first on the specific area that was selected by results from the geological survey. Many evidences far cavities were disclosed from this geophysical data. Therefore, a seismic tomography was tested on the target wet which was focused by results from the electrical resistivity Prospecting and was believed to have several large cavities. A distinct element numerical simulation using the UDEC was followed on the target area after completing all of field surveys. Data from field tests were directly dumped or extrapolated to numerical simulations as input data. It was verified from numerical analysis that several natural cavities underneath the foundation of the bridge should be reinforced Based on the project result, finally, most of fecundations far the bridge were re-examined and the cement grouting reinforcement was constructed on several foundations among them.

• Journal of the Korean GEO-environmental Society
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• v.20 no.8
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• pp.5-12
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• 2019

A pile group, that consists of several piles connected by a pile cap, is used as the superstructure. The pile supports vertical and horizontal load to design the pile group, but the effect of bearing capacity of the pile cap has not considered. Various researches have been conducted to reflect the effect of bearing capacity of the pile cap in order to reduce the amount of piles in the range of the stability under the vertical load of the superstructure. However, the effect of bearing capacity under the horizontal seismic load has not been studied adequately. Therefore, a shaking table test was carried out with different-sized pile caps that support the superstructure in this study. This test was to verify the influence of the size of the pile cap in the group pile under the horizontal load. The result shows that the size of the pile cap affects to the dynamic behavior of the superstructure and the pile group. Also, the bigger size of the pile group makes the larger constraint effect of ground, and it results that both the ground and the pile moves as a whole.

• Steel and Composite Structures
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• v.31 no.6
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• pp.629-640
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• 2019

The investigation of retaining wall structures behavior under dynamic loads is considered as one of important parts for designing such structures. Generally, the performance of these structures is under the influence of the environment conditions and their geometry. The aim of this research is to design retaining wall structures based on smart and optimal systems. The use of accuracy and speed to assess the structures under different conditions is one of the important parts sought by designers. Therefore, optimal and smart systems are able to have better addressing these problems. Using numerical and coding methods, this research investigates the retaining wall structure design under different dynamic conditions. More than 9500 models were constructed and considered for modelling design. These designs include height and thickness of the wall, soil density, rock density, soil friction angle, and peak ground acceleration (PGA) variables. Accordingly, a neural network system was developed to establish an appropriate relationship between data to obtain safety factor (SF) of retaining walls under different seismic conditions. Different parameters were analyzed and the effect of each parameter was assessed separately. According to these analyses, the structure optimization was performed to increase the SF values. The optimal and smart design showed that under different PGA conditions, the structure performance can be appropriately improved while utilization of the initial (or basic) parameters leads to the structure failure. Therefore, by increasing accuracy and speed, smart methods could improve the retaining structure performance in controlling the wall failure. The intelligent design process of this study can be applied to some other civil engineering applications such as slope stability.

• Korean Journal of Legislative Studies
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• v.24 no.2
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• pp.5-38
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• 2018

A seismic change is under way in diplomatic topography surrounding the Korean Peninsula. A new dynamic is being generated that could lead to a breakthrough in the nuclear stalemate and to an end of hostility between the two Koreas. Moon Administration's bold and creative foreign policy, which is alleged to place South Korea in the "driver's seat", is probably responsible for what is happening on the Korean Peninsula. However, on the other hand, Moon Administration's foreign policy shows a lot of continuity with foreign policy of previous conservative governments. In particular, the Moon government's emphasis on the vitality of the ROK-US alliance and its commitment to close coordination with the US in dealing with nuclear issues of North Korea is the hallmark of the continuity in South Korea's foreign policy. Emphasizing and sharing the notion of the continuities in foreign policy could contribute to social integration by garnering bi-partisan support. It could also spawn sense of stability, predictability, and confidence to diplomatic counterparts in other countries. And it could help avoid the negative effects of expectation-reality gap in the event that the outcome of all the diplomatic endeavor falls short of expectation held by citizens.

• Earthquakes and Structures
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• v.23 no.3
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• pp.259-269
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• 2022

In this study, we introduce a canonical correlation analysis method to accurately assess the tunnel damage potential of ground motion. The proposed method can retain information relating to the initial variables. A total of 100 ground motion records are used as seismic inputs to analyze the dynamic response of three different profiles of tunnels under deep and shallow burial conditions. Nine commonly used ground motion parameters were selected to form the canonical variables of ground motion parameters (GMP_CCA). Five structural dynamic response parameters were selected to form canonical variables of structural dynamic response parameters (DRP_CCA). Canonical correlation analysis is used to maximize the correlation coefficients between GMP_CCA and DRP_CCA to obtain multivariate ground motion parameters that can be used to comprehensively assess the tunnel damage potential. The results indicate that the multivariate ground motion parameters used in this study exhibit good stability, making them suitable for evaluating the tunnel damage potential induced by ground motion. Among the nine selected ground motion parameters, peck ground acceleration (PGA), peck ground velocity (PGV), root-mean-square acceleration (RMSA), and spectral acceleration (Sa) have the highest contribution rates to GMP_CCA and DRP_CCA and the highest importance in assessing the tunnel damage potential. In contrast to univariate ground motion parameters, multivariate ground motion parameters exhibit a higher correlation with tunnel dynamic response parameters and enable accurate assessment of tunnel damage potential.

• Journal of the Korean Geosynthetics Society
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• v.22 no.4
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• pp.9-15
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• 2023

Compaction is performed in civil engineering sites to secure the stability of the ground and prevent settlement. While the process of compaction is crucial, it is also essential to evaluate the degree of compaction after the completion of the process. In domestic sites, the evaluation of compaction is mainly conducted on a small number of spot using point-based tests such as plate load tests and sand cone tests. The methods presented so far allow assessment of surface compaction, but evaluating compaction in deeper layers poses challenges. Moreover, due to the limited coverage of point-based testing, it is difficult to achieve an overall assessment of compaction. As a solution to these issues, the Spectral-Analysis-of-Surface-Waves (SASW) tests were utilized to evaluate compaction. SASW tests offer a broader measurement range compared to point-based tests, and depending on the test setup, this method can provide the stiffness of the ground at greater depths. In this study, SASW tests were conducted in a compacted soil site under different conditions to assess compaction. Additionally, Nuclear Density Gauge tests were conducted concurrently to compare and verify the results of SASW. The research results confirmed the feasibility of evaluating compaction using SASW at the geotechnical site.