• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.33-45
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• 2021

In this study, predictive equations of the normalized shear modulus and the damping ratio curves for loose medium sands reinforced by vinyl strip-cement are proposed. Based on the results of a series of resonant-column tests (Yu, et al., 2018) conducted under the confining stresses of 15, 30, 60 kPa on sand specimens prepared with 40% relative density and reinforced by various contents of vinyl strip (0.0, 0.1, 0.3, 0.4%) and cement (0, 1, 2%), the equations estimating the normalized shear modulus and the damping ratio are proposed as functions of reinforcing conditions and confining stresses. The comparison between predicted and measured values of shear modulus and damping ratio shows a good agreement and the reliability of proposed predictive equations are validated by high R2-value greater than 0.9. Therefore, it is expected that the time and the cost required for constructing the normalized shear modulus and the damping ratio curves will be much reduced by using proposed equations in this study since those can easily be estimated without conducting resonant-column test.

• Journal of the Korean Geosynthetics Society
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• v.21 no.3
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• pp.61-69
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• 2022

In this study, a large-scale direct shear test was performed to evaluate the shear characteristics of the pile-soil interface according to the fines content and confining pressure conditions as a reasonable evaluation method of the pullout resistance performance of pile considering the soil conditions. It was found that the shear stress was greatly generated under the conditions of high normal stress and low fines content. In addition, the maximum shear stress was found to be rather large under the conditions of the same normal stress and fines content, when pile surface had high roughness. The internal friction angle decreased at the pile-soil interface, when the fines content in the ground increased. On the other hand, the cohesion decreased under the condition of high fines content. And the internal friction angle and cohesion were large regardless of the fines content in the model ground, when the roughness of the pile surface was high.

• Journal of the Korean Geotechnical Society
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• v.22 no.2
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• pp.41-53
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• 2006

The brittle materials like rocks show complicated strain-softening behavior after the peak which is hard to model using the classical constitutive models based on the relation between strain and stress tensors. A kinematically constrained three-dimensional microplane constitutive model is developed for granite. The model is verified by fitting the experimented data of Westerly granite and Bonnet granite. The triaxial behavior of granite is well reproduced by the model as well as the uniaxial behavior. We studied the development of the fracture zone in granite during blasting impact using the model with the standard finite element method. All the results obtained from the microplane model developed are compared to those from the linear elasticity model which is commonly used in many researches and practices. It is found that the nonlinearity of rocks sigificantly affects the results of analysis.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.61-71
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• 2006

A numerical procedure is presented fur evaluating seismic liquefaction on sloping ground sites. The procedure uses a fully coupled dynamic effective stress analysis with a plastic constitutive model called UBCSAND. The model was first calibrated against laboratory element behavior. This involved cyclic simple shear tests performed on loose sand with and without initial static shear stress. The numerical procedure is then verified by predicting a centrifuge test with a slope performed on loose Fraser River sand. The predicted excess pore pressures, accelerations and displacements are compared with the measurements. The results are shown to be in good agreement. The shear stress reversal patterns depend on static and cyclic shear stress levels and are shown to play a key role in evaluating liquefaction response in sloping ground sites. The sand near the slope has low effective confining stress and dilates more. When no stress reversals occur, the sand behaves in a stiffer manner that curtails the accumulated downslope displacements. The numerical procedure using UBCSAND can serve as a guide for design of new soil structures or retrofit of existing ones.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.111-120
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• 2006

In this research, numerical simulations by PFC considering discrete element method are conducted to predict experimental results of large triaxial compression test with rockfill material for dam construction. 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. To predict stress-stain behavior of large triaxial test, discrete particle modelling is applied with micro parameters which are chosen by calibration process. It is expected that distinct particle modelling method could be used as a useful tool to investigate micro and macro behavior associated with geotechnical problems and develop a numerical laboratory.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.5-15
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• 2009

Dynamic shear properties of Nak-Dong river sand were investigated to build a soil property database for Nak-Dong delta region. Samples were taken from the estuary and the midstream of the river. Laboratory specimens were prepared by air pluviation method, and were tested by using RC/TS apparatus at various confining stresses, relative densities and numbers of cycles. Shear modulus reduction and damping curves were developed using Ramberg-Osgood and Modified Hyperbolic Models. The developed curves, compared to those reported by other investigators, show only a slight difference. The outcome of this RC/TS experiments can be very important resources when accessing the dynamic response of sandy soils in Nak-Dong delta region in the future.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.69-85
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• 2009

It is very important to measure reliable dynamic properties of each zone in dam for seismic design. However, the Vs values of core and rock-fill zone are seldom determined by field test. Consequently, seismic design in dam is performed using Vs values assumed or empirically determined. So, it is required that reliable Vs has to be evaluated by in-situ test. In this study, surface wave method, which is nondestructive, was applied to dam to evaluate Vs profiles of core and rock-fill zone in dam. In 6 dams, using SASW and HWAW methods, Vs profiles were evaluated reliably. D/B of Vs profiles of each zone with depth and relationship between confining pressure and Vs profiles of rock-fill zone were constructed including existing results of other dams. The evaluated D/B and proposed relationship were compared with the frequently used empirical method by Sawada and Takahashi.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.133-140
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• 2010

A series of triaxial test was performed in order to determine critical state parameters of calcareous Jeju sand, which comprises angular shape particles with many pores in the surface. It is observed that Jeju sand mainly shows the contractive behavior during triaxial shear due to high extreme void ratios and large compressibility. The peak friction angle of Jeju sand decreases slightly with increasing mean effective stress due to the particle crushing of carbonate materials. However, the peak friction angle of Jeju sand is higher than that of other silica sands because of the more angular particle shape. The critical state friction angle of Jeju sand gradually decreases when the mean effective stress at a critical state increases. Whereas, there is not a clear influence of void ratio on the critical state friction angle. Critical state parameters of Jeju sand are similar to those of calcareous sands, but significantly larger than those of common sands.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.709-718
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• 2008

Developed is a chloride penetration analysis program in which changes of environmental conditions such as temperature, humidity and external chloride concentration, and the diffusion, convection and binding of chlorides are considered. In order to consider the changes of environmental conditions, analyses for temperature and moisture distribution are implemented simultaneously, and variation of diffusion coefficients due to temperature, humidity and age is also considered. By comparing the calculated total chloride contents with some experimental data, it has been confirmed that the proposed analysis program can trace measured chloride distribution well. Also, through some example analyses, the mechanism of accumulation of chlorides at near surface and acceleration of corrosion of steel reinforcement in case that the moisture distribution changes according to repeated drying and wetting cycles have been verified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.181-190
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• 2006

The behavior of artificially cemented sands were investigated by undrained triaxial test of isotropically consolidated sample. The cementation were induced by gypsum that is generally used for the aitificial cementation of sands. The gypsum of 5~20%(sand weight) were included in the sand and cured in the mold under the overburden pressure 55kPa. The yielding strength and stiffness of cemented sand were increased as the degree of cementation. And the dilation of sand was restricted by the cementation bonds, but after breakage of the bonds, it was increased more abrupt than the uncemented sands. The effective stress path showed that the aspects of effective pore water pressure were changed as the degree of cementation and the relative density. The effective stress ratio of cemented sand in the phase transformation line and the failure line were changed by the cementation. Generally the behavior of cemented sand more influenced by the degree of cementation than the relative density.