• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1377-1388
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• 2008

In our country where over 80% of land is mountainous, decomposed granite soils are often used as building materials for civil engineering works. Seashores are having great difficulties in management and treatment of marine byproducts that are left vulnerable. It is necessary to find a way to efficiently utilize such vulnerable marine byproducts. For this reason, shell and ocher were mixed together in order to efficiently utilize ocher that is being used frequently as a building material in civil works and shell that is a type of marine byproducts being thrown away. The purpose of this study is to examine the extent to which shell-ocher mixture can reduce liquefaction through cyclic triaxial test. The author of this study aims to provide the possibility for application at construction site of shell-ocher mixture.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.1
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• pp.67-75
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• 2024

In the case of the Pohang earthquake, which had a magnitude of 5.4 in 2017, geotechnical damages such as liquefaction and ground settlement occurred. The need for countermeasures has emerged, and experimental research in the Pohang area has continued. This study collected undisturbed samples from damaged fine-grained soil areas where ground settlement occurred in Pohang. Cyclic tri-axial tests for identifying the dynamic characteristics of soils were performed on the undisturbed samples, and the results were analyzed to determine the cause of ground settlement. As a result of the study, it was determined that in the case of fine-grained soils, ground settlement occurred because the seismic load as an external force was relatively more significant than the shear resistance of the very soft fine-grained soils, rather than due to an increase in excess pore water pressure.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.541-548
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• 2001

The interest in the dynamic properties of soils has increased strongly because of earthquake, heavy traffic, and foundations undergo high amplitude of vibrations. Most of soils in Korean peninsula are composed of granite soils, especially the decomposed mudstone soils are widely spread in Pohang areas, Kyong-buk province. Therefore, it Is very important to investigate the dynamic properties of these types of soils. The most important soil parameters under dynamic loadings are shear modulus and material dampings. Furthermore, few definitive data exist that can evaluate the behavior of unsaturated decomposed mudstone soils under dynamic loading conditions. The investigations described in this paper is designed to identify the shear modulus and damping ratio due to a surface tension for the unsaturated decomposed mudstone soils ulder low and high strain amplitude, For this purpose, the resonant column test and the cyclic triaxial test were performed. Test results and data have shown that the optimum degree of saturation under low and strain amplitude is 32 ∼ 37% which is higher than that of decomposed granite due to the amount of fine particles as well as the type and proportion of chief rock-forming minerals.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.852-855
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• 2010

Numerical simulations for large scale triaxial tests with large diameter rockfill materials are conducted using distinct element method. For generation of compacted assembly with specific grain size distribution and initial material porosity, the clump logic method and expansion of generated particles are adapted. With micro parameters which are chosen by calibration process, discrete particle modelling of triaxial test in case of other confining stress and cyclic loading condition were conducted. Also numerical simulations of fluid injection into particulate materials were conducted to observe cavity initiation and propagation using distinct element method. The fluid scheme solves the continuity and Navior-Stokes equations numerically, then derives pressure and velocity vectors for fixed grid by considering the existence of particles within the fluid cell.

• Geotechnical Engineering
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• v.14 no.3
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• pp.47-62
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• 1998

The disturbed state concept (DSC) proposed here is based on the idea that a deforming material element can be treated as a mixture of two constituent parts in the relative intact (Rl) and fully adjusted (FA) states, referred to as reference states. Based on this idea, DSC provides a unified constitutive model for the characteristics of saturated sands under cyclic loading. The model parameters for saturated sands are evaluated by using data from truly triaxial test device, The laboratory test results are also used for the verification of D SC model. In general, the model predictions are found to provide satisfactory correlation with the test results. From the results of this research, it can be stated that the DSC model is capable of characterizing the cyclic behavior of saturated sands under dynamic loading.

• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.64-75
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• 2017

The role of a track subgrade is to provide bearing capacity and distribute load transferred to lower foundation soils. Track subgrade soils are usually compacted by heavy mechanical machines in the field, such that sometimes they are attributed to progressive residual settlement during the service after construction completion of the railway track. The progressive residual settlement generated in the upper part of a track subgrade is mostly non-recoverable plastic deformation, which causes unstable conditions such as track irregularity. Nonetheless, up to now no design code for allowable residual settlement of subgrade in a railway trackbed has been proposed based on mechanical testing, such as repetitive triaxial testing. At this time, to check the DOC or stiffness of the soil, field test criteria for compacted track subgrade are composed of data from RPBT and field compaction testing. However, the field test criteria do not provide critical design values obtained from mechanical test results that can offer correct information about allowable permanent deformation. In this study, a test procedure is proposed for permanent deformation of compacted subgrade soil that is used usually in railway trackbed in the laboratory using repetitive triaxial testing. To develop the test procedure, an FEA was performed to obtain the shear stress ratio (${\tau}/{\tau}_f$) and the confining stress (${\sigma}_3$) on the top of the subgrade. Comprehensive repetitive triaxial tests were performed using the proposed test procedure on several field subgrade soils obtained in construction sites of railway trackbeds. A permanent deformation model was proposed using the test results for the railway track.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.307-317
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• 1999

The purpose of this study is to utilize conventional procedures for evaluation of liquefaction potential and to compare the results obtained by modified detailed method based on Korean earthquake magnitude (M=6.5). Liquefaction potential is assessed by comparing liquefaction strength of soil and cyclic shear stress generated in the soil layers during earthquakes. The cyclic shear stress is computed from the earthquake response analysis, and liquefaction strength of soil is evaluated by using results from cyclic triaxial tests. The cyclic triaxial tests are performed on many different conditions of sample ; relative densities(50%, 60%, and 70%), initial effective confining pressures (70kPa, 100kPa, and 150kPa), and fine contents(10%, 20%, and 30%). From the result of comparing the conventional procedure with the modified detailed method, it is found that the modified detailed method tends to evaluate larger safety factor against liquefaction in the weak sand site$(FS \leq1.5)$. Therefore in this case, it is suggested that liquefaction potential should be evaluated by using the modified detailed method based on cyclic triaxial tests. It is also found that in modified detailed method based on earthquake magnitude 6.5, critical depth where liquefaction can be generated is around 15m from the ground surface.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• Journal of the Korean GEO-environmental Society
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• v.23 no.5
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• pp.5-13
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• 2022

In this study, dynamic characteristics and liquefaction resistance characteristics of silica sand which is used to simulate sandy layer were conducted using the cyclic triaxial test according to the relative density difference. The difference in liquefaction resistance with the relative density was confirmed through the test results, which the relative density conditions were changed to 40%, 60%, and 80%, and the cyclic resistance ratio (CRR) curve of the silica sand was obtained. In addition, in order to examine the validity of the liquefaction resistance ratio (CRR) curve, artificial silica sand ground was created, and liquefaction potential was evaluated through the simple assessment method and the detailed assessment method, and the safety factors of each were compared.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5654-5663
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• 2015

In the unsaturated soil, suction, the negative pore water pressure leads to increases of the yield stress and the plastic shear stiffness of the soil skeleton due to the growth in interparticle stress. Therefore, in this study, the stress-strain relationship based on cyclic elasto-plastic constitutive model extended for unsaturated soil considering the 1st and the 2nd yield functions was induced in order to account for these effects of suction under the dynamic loading condition such as the earthquake. Through the program code considering this relationship and the routine of the cyclic loading with the reversion of loading direction, the numerical simulation of the cyclic triaxial test under the unsaturated condition would be possible. It is expected that the results of this study possibly contribute to the accuracy improvement on the prediction of unsaturated soil behavior under the dynamic loading condition.