• Geotechnical Engineering
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• v.11 no.4
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• pp.25-36
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• 1995

A specially designed model open -ended pile, which was composed of inner tube and outer tube, wry driven in the pressure chamber by two diffenent intallation methods, that is, impact -driving and vibratory driving, and static compression loading test was done for that pile. Through the measurement of bearing capacities in the separated resisting parts of open -ended pile, bearing mechanism of open-ended pile and soil plugging behaviors for different installation methods were studied. It appears that 20% out of soil plugging force of impact -driven pile was developed during driving, while the rest was developed during static compression loading and t.he magnitude of confining pressure applied to the chamber did not affect soil plugging behavior. Also. it appears that, soil plugging force of vibratory pile was not developed during driving, while it was developed weakly as about 0.5~0.7 times as that of impact pile during static compression loading. and the confining pressure of pressure rhamber had an effect on the soil plugging. In the ultimate loading condition unit soil plugging force did not approach to the failure condition.

• The Journal of Engineering Geology
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• v.32 no.2
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• pp.241-255
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• 2022

In this study, sieve analysis testing was performed on weathered granite soil from Yecheon (eastern South Korea) before and after water washing in accordance with the sieve analysis regulations of KS F 2302. The changes in particle separation and particle size distribution after washing with water were analyzed. Image analysis using an optical microscope revealed that soil particles were separated into smaller particles by water washing. The change in the particle size distribution curve was assessed using five index values. The increase in the fine particle fraction (<0.075 mm) was 13.67%, the increase in the 0.075-0.25 mm fraction was 19.44%, and the mean particle diameter (D₅₀) decreased by 0.663 mm. In addition, the maximum passage width (B_M) of the particle size distribution curve increased by 21.08% for the #30 sieve, and the moving area (A) of the particle size distribution curve was 69.28%·mm. These results suggest that washing with water is an effective way to prevent underestimation of the fine particle content in soil.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5C
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• pp.255-262
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• 2008

In order to investigate the strength anisotropy of compacted materials, a series of unsaturated and saturated-drained triaxial compression tests was performed. Three different orientation angles of the axial direction of samples with respect to the horizontal plane were investigated: ${\delta}=0$, 45 and 90 degrees. As the results showed, the suction rate on the strength of the unsaturated specimen was not influenced by ${\delta}$. And the effect of the angle ${\delta}$ on the strength was more pronounced on unsaturated specimen as compared to saturated specimen. Moreover, a new procedure was proposed to take into account the effect of the angle ${\delta}$ on the shear strength of unsaturated soils.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.5
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• pp.236-241
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• 2016

This study conducted a screening-level ecological risk assessment for heavy metals in dredged sediment for recycling in terrestrial environment. Toxicological information of six heavy metals (i.e., Cu, Zn, Cd, Pb, Cr, and Ni) was collected from ECOTOX of US Environmental Protection Agency, and screened and qualified for the use in the screening-level ecological risk assessment. According to the number of terrestrial ecological receptors for which toxicological information is available, PNEC (Predicted No Effect Concentration) of each heavy metal was derived using either stochastic approach (for Cu, Zn, and Cd), or deterministic approach (for Pb, Cr, and Ni). Hazard quotients of the six heavy metals were derived for a field-collected dredged sediment using the PNEC derived and the PEC (Predicted Environmental Concentration) determined for the dredged sediment. The HQs of Cu, Zn, Cr, Pb and Ni were higher than unity indicating a possibility of ecological risk of the five heavy metals when the dredged sediment is applied in terrestrial environment. Accordingly, remediation processes or a higher-level ecological risk assessment would be needed for the recycling of the material.

• International Journal of Highway Engineering
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• v.6 no.3 s.21
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• pp.17-26
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• 2004

The in-situ California Bearing Ratio (CBR) test has been widely used for evaluating the subgrade condition in asphalt concrete pavements. However, because the in-situ CBR test is expensive and takes plenty of time for operation, it is very difficult to figure out the in-situ characteristics of subgrade strength in detail. For faster and economical operation, the Dynamic Cone Penetrometer (DCP) has been often utilized for estimating the subgrade strength in the field. The relationship between the CBR value and DCP index obtained from the DCP testing has been studied using the laboratory and in-situ testing by other foreign researchers. The objective of this study is to determine the relationship between in-situ CBR value and DCP index of the subgrade materials used in Korea. The DCP index for evaluating the strength of subgrade materials produced in Korea is presented in this paper. Research results propose the regression equation to explain the relationship between the CBR and DCP tests. The in-situ CBR values of subgrade materials range from 20 to 45% indicating the good and sound subgrade condition.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.23-30
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• 2012

This paper is research results of slope stability analysis associated with seepage infiltration for unsaturated soil in debris-flow occurrence slopes. Site investigations were carried out in two slopes, located at Inje in Kangwon province where debris flow occurred in 2006 and at Yangpyung in Kyeunggi province where it occurred in 2010. For unsaturated soil sampled at the zone of debris-flow initiation, soil water characteristic curves with tempe pressure cells and shear strength parameters with newly designed shear strength apparatus were obtained respectively. The commertially available software SEEP/W was used to analyze seepage infiltration in unsaturated soil, based on their properties obtained from test results and the actual rainfall data at the moment of debris flow occurrence, and slope stability analysis with the program of SLOPE/W, associated with results of seepage analysis, was performed to simulate slope failure. As results of this research, seepage infiltration to unsaturated soil due to intensive rainfall was found to cause increase of ground water table as well as degree of saturation. Through this research slope stability analysis for unsaturated soil, considering the actual rainfall characteristic, might be a reasonable method of investigating characteristics of debris flow behavior, in particular, the moment of debris flow occurrence.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.28 no.3
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• pp.63-90
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• 2002

Quantitative measurement of melanin is the best method to evaluate whitening effect of cosmetics on human skin. However, non-invasive method to quantify human skin melanin with high precision has not been established. Whitening effect of cosmetics on the skin results in lightening of skin color. Therefore, it is reasonable to measure skin color in a reproducible manner for the assessment of whitening effect. Several Instruments or methods, such as colorimeter, mexameter, and visual assessments by experts , have been used for this purpose. In this lecture I will review the details of various assessment methods for the evaluation of whitening effect and discuss the pros and cons of each method. Then I will present briefly the results of clinical trial. Finally I will introduce new non-invasive modalities to quantify melanocytes.

• Proceedings of the Korean Association for Survey Research Conference
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• 2000.06a
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• pp.1-14
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• 2000

We consider statistical methods for nonresponse problem in social and economic sample surveys. To create a complete data set, which does not include item nonresponse data, imputation methods are generally used. In this paper, we introduce some imputation methods and compare them with one another. Also, we consider some problems, which occur when an imputed data set is treated as a response data set. Due to the imputed values, the true variance of the estimator after imputation is increased by the imputation variance. However, since usual naive variance estimator constructed from the imputed data set does not estimate the imputation variance, the true variance of the estimator after imputation tends to be underestimated. Theoretical reason is investigated and serious results are explained through a simulation study. Finally, some adjusted variance estimation methods to compensate for underestimation are presented and discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.287-291
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• 2004

가능최대홍수량(PMF)은 가능최대강수량(PMF)을 입력으로 한 강우-유출해석의 결과이다. 대상유역의 가능최대강수량을 산정하여 시${\cdot}$공간분포를 고려한 가능최대호우를 결정한 후, 강우-유출관계를 적용하여 가능최대홍수량을 산정하는 것이다. 이러한 과정을 통하여 산정된 가능최대홍수량은 실무에서 댐설계를 위해 이용되어 오고 있다. 하지만, 댐설계기준(건설교통부, 2001)에 가능최대홍수량 산정을 위한 방법론은 제시되어 있지만, 이에 내한 이론적인 토의가 충분치 않다. 본 연구에서는 국내의 가능최대홍수량 산정절차에 대한 문제점을 제시하고, 이에 대한 논의를 하고자 강우분포와 강우-유출매개변수에 따른 가능최대홍수량의 변화를 검토하였다. 먼저, 강우의 시간분포방법으로 blocking 방법, huff 방법, mononobe 공식을 채택하여 그 문제점을 세시하고, 시간분포방법별 가능최대홍수량의 변화를 비교${\cdot}$검토하였다. 강우-유출 매개변수에 따른 가능최대홍수량의 변화를 검토하기 위해서, 먼지 평균개념의 기존단위도와 최대개념의 단위도에 대해 평가하였으며, 두 단위도 적용에 따른 가능최대홍수량의 변화를 비교${\cdot}$검토하였다. 최대개념의 단위도는 강우-유출관계의 적용을 위해 그동안 우리나라에서 주로 이용되어 왔던 Clark 단위도를 선정하였고, 실측강우-유출자료의 해석을 통해 가능최대홍수량의 개념에 부합되는 매개변수를 산정하였다. 또한, 가능최대강수량의 차이, 강우손실방법, 기저유량 고려유무에 따른 가능최대홍수량의 변화를 검토하였다.

• Survey Research
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• v.1 no.2
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• pp.1-14
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• 2000

We consider statistical methods for nonresponse problem in social and economic sample surveys. To create a complete data set, which does not include item nonresponse data, imputation methods are generally used. In this paper, we introduce some imputation methods and compare them with one another. Also, we consider some problems, which occur when an imputed data set is treated as a response data set. Due to the imputed values, the true variance of the estimator after imputation is increased by the imputation variance. However, since usual naive variance estimator constructed from the imputed data set does not estimate the imputation variance, the true variance of the estimator after imputation tends to be underestimated. Theoretical reason is investigated and serious results are explained through a simulation study. Finally, some adjusted variance estimation methods to compensate for underestimation are presented and discussed.