• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.121-130
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• 1987

A new analytical method to determine the theoretical dispersion curves of Rayleigh wave in multilayered elastic media is developed. The method developed in this study gives the solutions for unlimited frequency, and is essential part of surface wave techniques to evaluate the layer profiles and dynamic properties of soils and pavement systems. Delta-Matrix technique is utilized to overcome the overflow and loss of precision problem inherent in the original Thomson-Haskell formulation at high frequencies. Conventional inversion methods based on the original Thomson-Haskell formulation lead to erroneous results due to the limitations on the layer profiles and the magnitude of frequency. The method developed in this study establishes the base of the research on more accurate and efficient inversion method, especially for the pavement systems as well as the natural soils.

• Computational Structural Engineering
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• v.6 no.1
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• pp.30-38
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• 1993

본문에서는 기계진동에 대한 말뚝기초의 설계에 대하여 간략하게 기술하였으며 본문에 기술된 방법들은 여러 가정들을 통하여 얻어진 것으로 경우에 따라서는 실제 거동과는 매우 상이한 거동을 예측할 수 있으므로 실제 설계에 이용되는 경우, 특히 주어진 지반의 물성치 선택 등에 주의를 요할 필요가 있다.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.221-230
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• 2017

We developed a polymer pouch using PVP that is water soluble in the precedent study. Yet melt viscosity was so low that it was not possible to produce hemispheric type which is essential for mass production, therefore we used another material to make the polymer pouch. It enabled to figure out a water-soluble transition and mechanic physical property of PEG that is newly chosen, and to blend the PEG with LLDPE and TALC followed by result. So, we could implement an evaluating property on blended proportion. It is important to find out a proper blending ratio throughout an experiment since its property is different or varied followed by each proportion as a water soluble character is conflict to a solid character. With the blending technique we were able to produce the polymer pouch enhanced for a tensile force and an impact intensity maintaining a water soluble character. We could identify a ground solidity effect of the polymer pouch as a result of a direct shear test using the product developed.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.407-418
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• 2003

It is necessary, in the light of the importance of long-term slope stability problem, to develop a simple method or tool which can figure out the possible failure surface resulting from weathering effect and other factors. The FBG(Fiber Bragg Crating) sensor system is used to estimate the correlations between the soil temperature and the slope behavior, and to find a failure surface in slopes effectively. This research is to seek for the correlation between the soil temperature distribution and the strain distribution of the reinforcing materials in an active zone by analyzing the data from the in-situ measurement so that the possible failure surface should be well defined based on the correlation. The zone of high temperature fluctuation can be regarded as one of the possible failure surface due to the weathering effect while the constant temperature depth of the ground, if exists, would not be relatively affected by the weathering process.

• Journal of the Korean GEO-environmental Society
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• v.5 no.1
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• pp.75-84
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• 2004

Stone column is one of the soft ground improvement method, which can enhance ground conditions such as the settlement reduction and the increasement of bearing capacity with applying the crushed stone instead of sand. In recent, general construction material, sand is in short of supply. Therefore, the bearing capacity improvement by the stone column is considered as the alternative method needed in many cases so the bearing capacity estimation is considered as important point. Nevertheless, adequate estimation methods to predict bearing capacity of stone column considering stone column and improvement effect of ground is not yet prepared. For the analysis of above mentioned points, the behavior of stone column were simulated as numerically on various property cases of crushed stone and surrounded ground. Through the numerical analysis of simulation results, the formula for the bearing capacity estimation of stone column was suggested. This formula was verified by comparing the prediction result of in situ test.

• Journal of the Korean Geotechnical Society
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• v.39 no.6
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• pp.5-12
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• 2023

Proactive assessment of landslide susceptibility is necessary for minimizing casualties. This study proposes a methodology for classifying the landslide safety factor using a classification algorithm based on machine learning techniques. The high-risk area model is adopted to perform the classification and eight geotechnical parameters are adopted as inputs. Four classification algorithms-namely decision tree, k-nearest neighbor, logistic regression, and random forest-are employed for comparing classification accuracy for the safety factors ranging between 1.2 and 2.0. Notably, a high accuracy is demonstrated in the safety factor range of 1.2~1.7, but a relatively low accuracy is obtained in the range of 1.8~2.0. To overcome this issue, the synthetic minority over-sampling technique (SMOTE) is adopted to generate additional data. The application of SMOTE improves the average accuracy by ~250% in the safety factor range of 1.8~2.0. The results demonstrate that SMOTE algorithm improves the accuracy of classification algorithms when applied to geotechnical data.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.1
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• pp.13-24
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• 2013

Various elastic wave-based site investigation methods have been used to characterize subsurface ground because the dynamic properties can be correlated with various geotechnical parameters. Although the inherent spatial variability of the geotechnical parameters affects the P-wave propagation characteristics, ground heterogeneity has not been considered as an influential factor. Thus, the effect of heterogeneous ground on the travel-time shift and wavefront characteristics of elastic waves through stochastic numerical analyses is investigated in this study. The effects of the relative correlation lengths and relative propagation distances on the travel-time shift of P-waves considering various intensities of ground heterogeneity were investigated. Heterogeneous ground fields of stiffness (e.g., the coefficient of variation = 10 ~ 40%) were repeatedly realized in numerical finite difference grids using the turning band method. Monte Carlo simulations were undertaken to simulate P-wave propagation in heterogeneous ground using a finite difference method-based numerical approach. The results show that the disturbance of the wavefront becomes more significant with stronger heterogeneity and induces travel-time delays. The relative correlation lengths and propagation distances are systematically related to the travel-time shift.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.103-110
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• 2020

In the recent seismic design code KDS 41 17 00, selection and modification procedures of ground motions which are used for nonlinear dynamic analyses were adopted. However, its practical applications are still limited due to the lack of literatures. This paper introduces case studies which used site-response analyses to select and modify ground motions for nonlinear dynamic analyses. Based on the case studies, design criterion for site-response analyses were reviewed thoroughly in the viewpoint of practical applications. It was found that design requirements related with bedrock motions are too conservative that ground motions are selected and modified in the excessive manner. It is especially true for low-rise building structures with period ranges including acceleration-sensitive regions. Even though surface motions have shown appropriate responses, such building structures have to re-select and re-modify ground motions based on pre-analysis procedures rather than post-ones according to the current seismic design code. Also, it was observed that building structures with soft soils under strong ground motions need more comprehensive investigations on soil properties and efficient analysis methods in order to perform site-response analyses. This is due to the fact that lack of reliabilities on soil properties and analysis methods could result in unstable site-responses.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.93-100
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• 2013

Frost heave occurs when ground temperature decreases under $0^{\circ}C$ and soil volume expands, which causes roadway and buried pipe line failure due to differential heaving. There are several models to predict volumetric strain caused by frost heave, but they requires expertises who have professional background and experience related to numerical analysis. This study presents an evaluation method to predict volumetric strain caused by frost heave with fundamental physical properties of soils. The evaluation method is assessed with experimental results.

• Geotechnical Engineering
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• v.3 no.4
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• pp.31-40
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• 1987

A helical probe test (HPT) suitable for in.situ soil exploration to a shallow depth and compaction control were developed and tested in different soils alongside traditional in-situ tests, including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and in-situ density test. The helical probe test is economical and can be performed by a single person. The torque necessary to insert the probe Is used as a measure of soil characteristics. It was found that: the HPT test correlates well with the SPT test and the correlation is not sensitive to the soil type; the HPT test correlates well with the CPT test, but the correlation is sensitive to the soil type; the HPT torque provides a sensitive measure of relative compaction rind in-situ dry density of compacted soils; the reverse torque ratio decreases with increasing average grain sloe.