• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.41-52
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• 2012

Suction drain method can directly apply vacuum pressure to the soft ground through vertical drains so it can make hardening zones around them. These hardening zones make steeply lower the discharge efficiency of the pore water with decreasing permeability. This paper considered a stepped vacuum pressure to minimize a hardening zone which is one of the important parameters that can decrease discharge efficiency. A series of laboratory tests were conducted in order to examine the effect of the hardening zones and to evaluate their effects to the ground improvements with varying durations which applied stepped vacuum pressures(-20kPa, -40kPa, -60kPa and -80kPa) with Busan marine clay. According to strength(CPT), water content test and theoretical investigation indicate a size of the hardening zone within 7cm and the decreasing ratio of permeability about 2.0~4.0. Also, the total settlements are larger for the stepped vacuum pressure than the instant vacuum loading. The application time with vacuum pressure is determined considering the geotechnical properties of the interested clays. Results of numerical analysis show that consolidation behavior is appropriate to measurement for considering hardening zones.

• Geotechnical Engineering
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• v.12 no.2
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• pp.95-106
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• 1996

In this study, a constitutive model which can describe the anisotropic and plastic behaviors of natural cohesive soils, was developed based on anisotropic bounding surface theory. The model was fomulated by the concepts of the improved anisotropic bounding surface function, nonassociated flow rule with new plastic potential function, anisotropic hardening rule, and new mapping rule governing the plastic behavior inside bounding sutraface. Comparing with the results of Ku consolidation and triaxial shearing tests, the predictions by the proposed model agree quite well with real soil responses.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.170-171
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• 2019

When the cement paste in concrete is exposed to high temperatures, the mechanical performance decreases due to a series of reactions inside the cement. In this study, we investigated the change of nanostructure of $C_3S$ when $C_3S$ was exposed to high temperature using pair distribution function (PDF) based on high energy X-ray scattering. As a result of X-ray diffraction, there was no significant difference when $C_3S$ was heated at $300^{\circ}C$, but most of $Ca(OH)_2$ was decomposed into CaO at $500^{\circ}C$. In addition, it was confirmed that CaO is dominant in the nanostructure when $C_3S$ is heated to $500^{\circ}C$.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.378-379
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• 2019

본 논문은 LCL 필터를 사용하는 3상 계통연계 인버터의 그리드 전류 오차를 개선하고 고조파 왜곡 현상을 억제하기 위해 다중 공진제어 기법을 슬라이딩 평면에 적용한 슬라이딩 제어기(SMC)를 제시한다. 일반적으로 시스템 파라미터가 변경되거나 계통에 외란이 발생할 경우 슬라이딩 평면이 표류하는 현상이 나타나며 이러한 표류 현상은 시스템 정상상태 오차와 시스템에 고조파 왜곡 현상을 일으키고 계통연계 인버터의 전류 품질에 심각한 영향을 미치게 된다. 이러한 현상을 해결하기 위해 적분 함수가 추가된 SMC가 제안되었으나 해당 제어기는 효과적으로 정상상태 오차를 제거하는 반면 슬라이딩 평면의 표류현상을 충분히 줄여주지 못하는 한계를 가지고 있다. 이러한 정상상태 오차와 표류현상을 제거하기 위해 다중 공진제어 조건을 슬라이딩 평면 함수에 추가한 제어기를 제시한다.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.87-98
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• 2013

This study was performed a series of the isotropic compression-expansion tests and the drained triaxial tests with various the relative densities 40%, 60%, 80% and 95% for bottom ash. Using the tests results the characteristic of the parameters of Lade's single hardening constitutive model were investigated. The soil parameters Kur and n representing elastic behavior are not much affected by the change of the relative density. The other parameters such as failure criterion(m, ${\eta}_1$), hardening function(c, p) and plastic potential(${\psi}_2$, ${\mu}$) are in a positive linear relationship with the relative density. Since the soil parameters h and ${\alpha}$ representing yield function do not change much to the change of relative density and also closely related to failure criterion, they can be replaced by failure criterion ${\eta}_1$. We also observed that predicted values from the Lade's single hardening constitutive model were well consistent with the observed data.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.29-36
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• 2011

In this study, a series of the isotropic compression-expansion tests and the drained triaxial tests were performed on Pocheon granite soil with various the dry densities of $16.67kN/m^3$, $17.26kN/m^3$ and $17.65kN/m^3$. Using the tests results the characteristic of the parameters of Lade's single hardening constitutive model were investigated. The soil parameters such as kur and n related to elastic behavior, m and ${\eta}_1$ related to failure criterion, c and p related to hardening function and ${\psi}_2$ and ${\mu}$ related to plastic potential show in a positive linear relationship with the dry density. Since the soil parameters h and representing yield function do not change much to relative density and also are closely related to failure criterion, they can be replaced by failure criterion. We also observed that predicted values from the Lade's single hardening constitutive model were well consistent with the observed data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1C
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• pp.11-17
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• 2011

This study was performed a series of the isotropic compression-expansion tests and the drained triaxial tests with various the relative densities 25%, 50%, 80% and 100% for Baekma river sand. Using the tests results the characteristic of the parameters of Lade's single hardening constitutive model were investigated. The soil parameters Kur and n representing elastic behavior are not much affected by the change of the relative density. The other parameters such as failure criterion (m, ${\eta}_1$), hardening function (C, p) and plastic potential (${\Psi}_2$, ${\mu}$) are in a positive linear relationship with the relative density. Since the soil parameters h and $\alpha$ representing yield function do not change much to the change of relative density and also closely related to failure criterion, they can be replaced by failure criterion ${\eta}_1$. We also observed that predicted values from the Lade's single hardening constitutive model were well consistent with the observed data.

• Journal of the Korean Wood Science and Technology
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• v.42 no.1
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• pp.49-57
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• 2014

The pre-air-drying of Korean pine before the high-temperature and low-humidity drying was shown to be effective in uniform moisture content distribution and prevention of surface check. Our results suggest that initial moisture content of the timber also plays important role in high-temperature and low-humidity drying method. The pre-air-drying also helps in the reduction of surface checks in Korean pine when compared to the Korean pine dried by only high-temperature and low-humidity. End-coating was not effective in the prevention of twist, shrinkage, case hardening and internal checks. The pre-air-drying reduces the internal tension stresses which occur during high-temperature and low-humidity drying thus decreasing case hardening and also preventing internal checks. The pre-air-drying decreases the moisture content and causes shrinkage which leads to increased twist in the Korean pine.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.859-869
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• 2009

The sharp indenters such as Berkovich and conical indenters have a geometrical self-similarity in theory, but different materials have the same load-depth curve in case of single indentation. In this study, we analyze the load-depth curves of conical indenter with angles of indenter via finite element method. From FE analyses of dual-conical indentation test, we investigate the relationships between indentation parameters and load-deflection curves. With numerical regressions of obtained data, we finally propose indentation formulae for material properties evaluation. The proposed approach provides stress-strain curve and the values of elastic modulus, yield strength and strain-hardening exponent with an average error of less than 2%. It is also discussed that the method is valid for any elastically deforming indenters made of tungsten carbide and diamond for instance. The proposed indentation approach provides a substantial enhancement in accuracy compared with the prior methods.

• Journal of the Institute of Convergence Signal Processing
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• v.13 no.3
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• pp.119-129
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• 2012

In the medical field, the hardening of tissues is one of important informations used in diagnosis or understanding progress of disease, a quantitative measuring method of hardening is important for objective diagnosis. It has been proposed MRE(Magnetic Resonance Elastography) method that measures an index of hardening, viscoelastic properties in a noninvasive. Because the S/N ratio of MRE images go down when measuring viscoelastic properties from local wavelength and local damping factor of a propagating wave in MRE method, methods using multiple phase MRE images have been examined to decrease the effect of noise. We propose a method measuring viscoelastic properties after Fitting a function for multiple phase MRE images in this research. This proposed method has a advantage to set up arbitrarily the variation rate of a space direction of viscoelastic properties or the spatial resolution of measuring values according to changing of the noise included in images, though it applies viscoelastic wave for multiple phase MRE images. We confirmed the effectiveness of a proposed method by experiment using simulation images and experiment using silicone-gel phantom.