• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.4
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• pp.51-57
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• 2006

This study was carried out to investigate the soil water characteristic curve and prediction of void ratio with net stress and matric suction using the linear elastic and volumetric deformation analysis method on unsaturated silty. The unsaturated soil tests were conducted using a modified oedometer cell and specimens were prepared at water content 2 times of liquid limit and required void ratio. The axis translation technique was used to create the desired matric suctions in the samples. It is shown that soil water characteristic curve and volumetric water content were affected significantly by preconsolidation pressure. As a matric suction increases, the reduction ratio of void ratio was shown to considerably small. Also, the predicted and measured void ratio for unsaturated soils using the linear elastic and volumetric deformation analysis showed good agreement as net stress and matric suction increases.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.65-76
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• 2014

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.281-287
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• 2005

Nonlinear behaviors such as steep-fronted wave motions and a finite amplitude limit cycle often accompanying combustion instabilities have been numerically investigated using a characteristic-based approximate Riemann solver and the well-known ${\eta}-{\tau}$ model. A resonant pipe initially subjected to a harmonic pressure disturbance described the natural steepening process that leads to a shocked N-wave. For a linearly unstable regime, pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions. For the 1.5 MW gas generator under development in KARI, the numerical results show good agreement with experimental data from hot-firing tests.

• Journal of the Korean Geosynthetics Society
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• v.23 no.1
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• pp.39-47
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• 2024

In this study, physical property tests and standard consolidation tests were conducted on the marine clay of Busan New Port and North Port, the middle and lower reaches of the Nakdong River including Gimhae and Yangsan, and Ulsan regions. The moisture content, a property unrelated to sample disturbance with small individual test errors, was used for regression analysis with the compression index, virgin compression index, consolidation coefficient, expansion index, and secondary compression index, among others. Subsequently, the correlation and accuracy were evaluated. Upon analyzing the correlation between the moisture content, void ratio, and liquid limit commonly used physical properties for calculating compression indexes, it was confirmed that the liquid limit had the lowest correlation. Through a linear regression analysis of the consolidation constants using the current moisture content in the natural state, a high correlation was demonstrated. Relationship equations were then presented to determine settlement and settlement time. This study suggests that moisture content can be utilized as an alternative for evaluating and calculating consolidation constants when examining ground settlement in sedimentary clays distributed in the Busan and Gyeongnam regions.

• Geotechnical Engineering
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• v.12 no.1
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• pp.21-34
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• 1996

This paper presents the engineering characteristics of the Samcheok organic soil which contains a large portion of organic matter and high natural water content. A series of lab tests shows that the measured liquid limit is quite different depending on preparing methods of specimens. The values tested with natural condition are higher up to 4 times than thole of the oven dry specimen. It is shown that the organic soils fail at large strain and do not show peak stress in the stress strain relationships. Also strength increase ratios, which are measured 0.43 to 0.65 in this tests, are significantly higher than those of the soft clay without organic matter. The consolidation tests indicate that the verti'cal and horizontal Permeabilities are almost the same. For the remolded samples is reduced from 112 to 116 of the vertical permeability An increase of organic matter or water content of the organic soils results in an increase of the coefficient of secondary consolidation. The increase rate is slow below 15 percents of the organic contents while the rate becomes higher above the value.

• Journal of the Korean Geotechnical Society
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• v.35 no.8
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• pp.43-56
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• 2019

This research has been conducted to suggest an estimation equation of compression index to be practically applied to the southeastern areas by finding out physical and mechanical characteristics of 229 points on the southeastern coast areas (Busan area: 78 points, Gimhae area: 103 points, Geoje area: 18 points, Changwon area: 30 points) through indoor tests and analyzing its relation to the compression index. From the results, we could not only find out correlation between natural water content, liquid limit and initial void ratio versus compression index for soft ground on each of the southeastern coast areas, but also an integrated correlation equation of the southeastern coast areas. In addition, we have performed a comparative analysis of the existing estimated equation of compression index and that found in this paper. As a result, the existing estimated equation suggested by foreign researchers has shown considerable error to be applied to the soft ground on the southeastern coast areas in Korea. The estimated equation of compression index with the water content out of the existing estimated equations has shown minimum 10.8% to maximum 48.1% of error rate, minimum 13.4% to maximum 288.5% of error rate with liquid limit or minimum 9.4% to maximum 211.4% of error rate with initial void ratio. On the other hand, error rates calculated with the estimated equations of compression index from this research have shown minimum 10.5% to maximum 13.4% with water content, minimum 11.6% to maximum 21.3 with liquid limit or minimum 7.1% to maximum 11.7% with initial void ratio, for better results than those with existing estimated equations. In addition, relation between compression index and expansion index has shown Cs = (1/5 ~ 1/12)Cc similar to the existing relation of Cs = (1/5 ~ 1/10)Cc.

• Korean Journal of Medicinal Crop Science
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• v.24 no.4
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• pp.271-276
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• 2016

Background: In the present study, we established an HPLC (high performance liquid chromatography)-analysis method for the determination of marker compounds as a part of the material standardization for the development of health-functional foods from Salvia plebeia R. Br. extract. Methods and Results: The quantitative determination method of hispidulin as a marker compound was optimized by HPLC analysis using a YMC hydrosphere C18 column with a gradient elution system. This method was validated using specificity, linearity, accuracy, and precision tests. It showed a high linearity in the calibration curve with a coefficient of correlation ($r^2$) of 0.999995. The method was fully validated, and was sensitive, with the limit of detection (LOD) at $0.09{\mu}g{\cdot}m{\ell}^{-1}$ and limit of quantification (LOQ) at $0.27{\mu}g{\cdot}m{\ell}^{-1}$. The relative standard deviation (RSD) values of the data from intra- and inter-day precision were 0.05 - 0.22% and 0.32 - 0.42%, respectively, and the intra- and inter-day accuracy of hispidulin were 99.5 - 102.3% and 98.8 - 101.5%, respectively. The average content of hispidulin in Salvia plebeia R. Br. extract was $3.945mg{\cdot}g^{-1}$ (0.39%). Conclusions: These results suggest that the developed HPLC method is very efficient, and that it could contribute to the quality control of Salvia plebeia R. Br. extracts as a functional ingredient in health functional foods.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.1
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• pp.102-111
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• 1997

Experiments both in laboratory and field were performed to compare and analyze the characteristics of alluvial clay. The alluvial clay was sampled in test site in which large-scaled tests for the part of the site are under process to suggest the rational method for alluvial clay and the criterion for ground settlement monitoring system. The followings were observed through the experiments : 1. Natural water content, plastic limit, and liquid limit of alluvial clay composed of highly fine grains were 40~80%, 10~20%, and 30~55%, respectively. The values of these properties were relatively small at the ground surface, while the values showed maximum at G.L.- l0m and gradually decreased below the level. 2. Shear strength of alluvial clay was proportionally increased to the depth. Unconfined and triaxial compressive strengths were 0.2~0.6kgf/$cm^2$ and 0.1~0.3kgf/$cm^2$, respectively. 3. Compression index and secondary compression index showed maximum values at G.L.-l0m and gradually decreased below the level. The value of consolidation coefficient was relatively large at the ground surface, constant with decreasing the depth, and incresed when G.L. was below -20m. 4. Piezocone test appeared that alluvial clay with N value of 2~4 was uniformly distributed with 20~ 30m thickness from the ground surface, sand seam was nonuniformly distributed, and penetration pore pressure was 0.8 ~ 1 times of the hydrostatic pressure. Undrained shear strength and consolidation coefficient were 0.04 ~ 0.76kgf / $cm^2$ and $2.88{\times} 10{^-4}~1.3{\times} 10{^-2} cm^2/s$ respectively.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.2
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• pp.43-53
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• 1989

In this research programs, a series test was conducted to show the effects of freeze/thaw process on the various soil properties. The tests were carried out taken from the west sea shore of Korean peninsular and the west sea shore of Scotland, and their results are as follows; 1. There was a positive total heave in a freezing run, although water may he expelled for the sample initially. The water flow must he reverse' from expulsion to intake. 2. The confining pressure had an overriding influence on the heave and frost penetration, a sudden change of the axial strain at failure with strain rate was observed occuring at a strain rate between 10-5 and 10-6, and the initial friction angle of frozen clay was appeared zero. 3. There was shown a significant decrease in liquid limit of soil which was subjected to freeze/thaw process for the initial value of about 20% because of soil particles aggregation. 4. The cyclic freeze/thaw caused a sinificant reduction in shear strength and its thixotropic regain. The frozen/thawed soil exibited negative strength regain, particularly at high freeze/thaw cycles. 5. The freezing temperature greatly influenced on the failure strength of soils and this. Trend was more pronounced the lower the freezing temperature and shown the ductile failure with indistinct peaks.

• Nuclear Engineering and Technology
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• v.38 no.2
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• pp.139-146
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• 2006

An experimental study was performed to evaluate the effects of surface coating and an enhanced insulation structure on the downward facing boiling process and the critical heat flux on the outer surface of a hemispherical vessel. Steady-state boiling tests were conducted in the Subscale Boundary Layer Boiling (SBLB) facility using an enhanced vessel/insulation design for the cases with and without vessel coatings. Based on the boiling data, CHF correlations were obtained for both plain and coated vessels. It was found that the nucleate boiling rates and the local CHF limits for the case with micro-porous layer coating were consistently higher than those values for a plain vessel at the same angular location. The enhancement in the local CHF limits and nucleate boiling rates was mainly due to the micro-porous layer coating that increased the local liquid supply rate toward the vaporization sites on the vessel surface. For the case with thermal insulation, the local CHF limit tended to increase from the bottom center at first, then decrease toward the minimum gap location, and finally increase toward the equator. This non-monotonic behavior, which differed significantly from the case without thermal insulation, was evidently due to the local variation of the two-phase motions in the annular channel between the test vessel and the insulation structure.