• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1268-1277
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• 2008

Recently, the high speed railway comes into the spotlight as the important and convenient traffic infrastructure. In Korea, Kyung-Bu high speed train service began in about 400km section at 2004, and the Ho-Nam high speed railway will be constructed by 2017. The high speed train will run with a design maximum speed of 300-350km/hr. Since the trains are operated at high speed, the differential settlement of subgrade under the rail is able to cause a fatal disaster. Therefore, the differential settlement of the embankment must be controlled with the greatest care. Furthermore, the characteristics and causes of settlements which occurred under construction and post-construction should be investigated. A considerable number of studies have been conducted on the settlement of the natural ground over the past several decades. But little attention has been given to the compression settlement of the embankment. The long-term settlement of compacted fills embankments is greatly influenced by the post-construction wetting. This is called 'hydro collapse' or 'wetting collapse'. This wetting collapse problem for the compressibility of compacted sands, gravels and rockfills, has been recognized by several researchers. For this wetting settlement problem, we showed the test results carried out with 4 fill materials. These tests were performed under the condition that the fill materials were inundated at the first wetting. Subsequently, in this study, we investigated the long-term settlement characteristics of the fill materials under the repeated partial wetting and rising of the ground water table happend by rainfall.

• Journal of Plant Biology
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• v.11 no.4
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• pp.1-8
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• 1968

The persent paper discusses the relation between water pollution and aquatic organisms resulted from the study of the water quality and the kinds of algea and aquatic insects both of the An-yang River from Mt. Kwan-ak to the Han River and of the Kock-neung River from Mt. Puk-han to the Han River during the spring of 1965 and 1966. According to the change of water quality, the An-yang River might be divided into three areas. In the first area, from Mt. Kwan-ak to near An-yang town, water quality is not so polluted that may aquatic organisms such as Anisogamarus ryotoensis, Epeorus, Cambaroides, Zygnem, Batrachospermum moniliform, Draparnaldia glomerata are found. In the second area where water is polluted by the inflow of sewerage water from An-yang town, the concentration of chloride, COD, ammonia-N, nitrate-N, alkali degree increased. Therefore, few aquatic insects and algea are found. In the third area, it is much polluted by the industrial sewerage water frojm Yeong-dong-po; and so the aquatic organisms that indicate strong pollution such as Oscillatoria, Euglena, Tubifex are found in this area. It is also significant that the Nereis japonica that indicates the pollution of brackish water is discorved in the some area. In the case of the Kock-neung River, however, it is not clearly divided into areas, as in the case of the An-yang Riber, according to the pollution of water; but because of villages and towns along the river the gradual pollution of water; but because of villages and towns along the river the gradual pollution of water is observed and accordingly, a considerable change in aquatic organisms is also found in this river. In the area near II-yeung town, for instance, the concentration of the chloride, hardness, nitrite, nitrate is very low, and ammonia-N is not detected; and accordingly the aquatic insects that generally inhabit in mountain stream, such as Anisogamarus ryotoensis, Cambaroides, Epeorus, Thraubs, Hydropsyche are found here. In the down stream of the river, from Kock-chon, the quality of water is considerably polluted and fine sands are found laid on the bottom of the stream; therefore, the aquatic insects are very few, but the algea such as Navicula, Pleusigma, Oscillatoria that indicate water pollution are found in this area.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.141.1-141.1
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• 2012

CIBER (Cosmic Infrared Background ExpeRiment) is a sounding-rocket borne experiment which is designed to find the evidence of the First stars (Pop.III stars) in the universe. They are expected to be formed between the recombination era at z ~ 1100 and the most distant quasar (z ~ 8). They have never been directly detected due to its faintness so far, but can be observed as a background radiation at around $1{\mu}m$ which is called the Cosmic Near-Infrared Background (CNB). The CIBER is successfully launched on July 10, 2010 at White Sands Missile Range, New Mexico, USA. It consists of three kinds of instruments. One of them is a LRS (Low Resolution Spectrometer) which is a refractive telescope of 5.5 cm aperture with spectral resolution of 20 ~ 30 and wavelength coverage of 0.7 to $2.0{\mu}m$ to measure the spectrum of the CNB. Since LRS detects not only CNB but also stellar components, we can study their spectral features with the broad band advantage especially at around $1{\mu}m$ which is difficult at ground observations because of the atmospheric absorption by water vapor. I identified around 300 stars from observed six fields. If we can classify their spectral types with SED fitting, we can study their physical conditions of the stellar atmosphere as well as making a stellar catalogue of continuous stellar spectrum.

• Geotechnical Engineering
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• v.2 no.3
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• pp.27-36
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• 1986

To investigate the seepage effect on the compacted backfill of retaining walls, an expriment and an analytical study were carried out First, the expriment was performed with a two-way permeameter newly designed for the do- termination on the degree of permeability anisotropy of compacted soils. As a result, e-log(kz/ky) plot showed a linear relationship, where kz and ky were permeability coefficients for the normal and the parallel directions to the compaction. The degree of permeability anisotropy, kz/ky was 2 to 4 at Dr>90% for sands, regardless of the methods of compaction. The kz/ky of the fine sand was greater than that of the coarse sand. Second, the exprimental results were applied to the extention of Gray's theory for the investigation of the active thrust affected by the seepage of permeability anisotropy. The active thrust was decreased with the increase in the degree of permeability anisotropy, and it It.as a little effect on wall friction.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.17-25
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• 2011

In this study, we considered the bearing capacity of strip footing over clay layers partially replaced by sand. The FEM analysis is performed to calculate the ultimate bearing capacity. Partial replacement is defined by multiples of footing width(B) and inclination of sides. The cases(B'=inf.) of sand layers equal to clay layers are preferentially conducted. The baring capacity of B'=inf. is comparative value for bearing capacity of partial replacement layers. ${\beta}$ is the ratio of ultimate bearing capacity of B'=inf and partial ultimate bearing capacity replacement. ${\beta}$ is used to analyze the characteristic of bearing capacity of clay layers partially replaced by sand. Each of the three undrained shear strengths of clay and friction angles of sand is considered. The result of this analysis shows that ${\beta}$ depends on sand depth.

• The Korean Journal of Ecology
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• v.26 no.3
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• pp.97-102
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• 2003

This study was carried out to understand the variation of bird community by eco-park development of urban stream, Yangjae stream, Seoul, from Jan. 1996 to Dec. 2001. After the development, slight change in the bird community happened; for example, the number of species increased(r²=0.729, p<0.05), but there was not any variation in the total number of birds(r²=0.050, p>0.05). Especially, the number of individuals in herons and ducks rose. We suggest that the change as caused by restoration of low revetment vegetation and artificial pond vegetation in flood plain. However, the number of sandpipers, plovers and wagtails inhabiting on the sands and gravels in stream fell down. It seems that it would be caused by construction of bicycle path on the flood plain. The number of songbirds was tended to go down to 2000, but increased in 2001. The decrease of songbirds might be attributed to irregular removals of bush. We suggested that riparian vegetation restoration and artificial ponds positively affected birds inhabitation, but bicycle path and irregular elimination of a bush negatively affected.

• Journal of the Korean GEO-environmental Society
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• v.13 no.8
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• pp.65-73
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• 2012

Soil-rock interface, mainly founded in Granite region of Korea, is known as one of the important factor of the slope failure at the rainfall due to smaller shear strength than soil itself. However, research of the effect on slope stability by soil-rock interfaces is insufficient. Therefore, a series of direct shear tests were performed in order to investigate the effect of soil-rock interface on slope stability. The method of tests is to get sand itself and sand-artificial rock interface shear strength from different grain size of sands and artificial rock samples. The results of tests show that the friction angle of interface depends primarily on particle size and surface roughness. Interface friction angle ratio ${\mu}(={\delta}/{\Phi})$ is in the range of 0.75 ~ 0.96, this results indicate that interface friction angle is smaller than sand itself.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.4
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• pp.31-38
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• 2002

The rate of sewage treatment in South Korea was 68% in the late 1999. Sewage treatment is mostly made near big cities such as Seoul and Busan, and it is little in rural areas. Wastewater from households goes to streams directly without treatment in rural areas and pollutes streams. It is necessary to improve the progress for treatment of nutrients such as N and P which cause eutrophication in streams and lakes, because sewage treatment system in South Korea focuses on treatment of basic organic matters. Therefore it will contribute to improve discharged water quality if small sewage treatment systems by aquatic plants and microbes are introduced to rural areas where are not connected to local sewage treatment facility. This experiment was conducted to find out the best way using aquatic plants and microbes to purify wastewater from households through individual sewage treatment system. Phragmites communis, Iris pseudoacorus, Acorus calamus var. angustatus, Typha orientalis and Oenanthe javanica were used for this experiment. BOD, COD, SS, T-N and T-P were analyzed following standard methods for wastewater. The result shows that wastewater was roughly purified through pebbles and sands, and highly purified through aquatic plants and microbes especially in T-N and T-P. Iris pseudoacorus is the most effective in reduction of COD and BOD level. This system will work even in winter when plants die because microbes will be still working.

• Economic and Environmental Geology
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• v.49 no.3
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• pp.225-242
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• 2016

Rock physics serves as a useful tool for seismic reservoir characterization and monitoring by providing quantitative relationships between rock properties and seismic data. Rock physics models can predict effective moduli for reservoirs with different mineral components and pore fluids from well-log data. The distribution of reservoirs and fluids for the entire seismic volume can also be estimated from rock physics models. The first part of this report discusses the Voigt, Reuss, and Hashin-Shtrikman bounds for effective elastic moduli and the Gassmann fluid substitution. The second part reviews various contact models for moderate- to high-porosity sands. In the third part, constant-cement model, known to work well for the sand that gradually loses porosity with deteriorating sorting, was applied to the well-log data from an oil field in the North Sea. Lastly, the rock physics template constructed from the constant-cement model and the results from the prestack inversion of 2D seismic data were combined to predict the lithology and fluid types for the sand reservoir of this oil field.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.57-68
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• 2014

This study categorizes the distributed sand around coastal area of Jeju volcanic Island into three groups according to their components, and arranges their characteristics. In the case of basic physical properties, the silicate sand has slightly greater specific gravity than general sand, and the carbonate sand with widespread distribution has a lower specific gravity. In the gross, the carbonate sand has poor particle classifying and low uniformity coefficient because carbonate minerals of relatively large grain size are mixed. The relation between compressive strength and components shows conflicting tendency that silicate and carbonate components have positive correlation and negative correlation with compressive strength, respectively. Based on the components ratio of one to one, the sand having low carbonate component ratio is expected to be able to utilize in construction fine aggregate. To compare between square root (ACI 308) and cube root (KCI 2012) of compressive strength at computation of elastic modulus, it is considered to non-dimensional elastic modulus.