• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.45-52
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• 1999

It is difficult to keep the balance of supply and demand for natural aggregates in recent years, because natural resources have become to be almost exhausted. Crushed stone is already used for coarse aggregate instead of river gravel at present. Now, crushed sand or sea sand should be used for fine aggregate, because natural sand also has been exhausted with a few exceptions around Nakdong River. The sea sand has a lot of problems which are the corrosion of reinforcement bars, the investment of facility for cleansing salt and the cost increase due to the insufficiency of industrial water. Therefore, it is necessary to produce and to utilize the crushed sand very actively, but some material properties which are related to water absorption, strength and chemical durability, prevent from determining the generalized criteria because its rocks make much differences in its physical and chemical characteristics. In this paper, fundamental physical properties of crushed sand, which comes from Daegu Subway construction fields, have been investigated for the usability on basic material of concrete. The optimum replacement ratio and the strength estimation method of crushed sand replacing natural sand also have been presented here through the compressive strength test of ready-mixed concrete cylinders.

• Journal of Korean Society on Water Environment
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• v.33 no.4
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• pp.460-473
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• 2017

In order to certificate the contamination assessment of heavy metals in surface sediments from the Nakdong river. Surface sediments were collected of 24 sampling sites (main 14st., tributary 10st.) and analyzed for grain size heavy metals contents. Study area mainly composed of sand (avg. 94.1%) and mean grain size was $1.46{\Phi}$ on average. Heavy metals contents (avg. Al: 12.5%, Zn; 74.4, Cr: 45.3, Li: 26.0, Pb: 17.1, Ni: 10.5, Cu: 7.8, Cd: 0.22 mg/kg) were relatively high contents in the composed of fine sediments. In addition, the results of pearson's correlation coefficient showed that most heavy metals and grain size (silt and clay) were highly correlated. The contents of Zn (6st.) and Ni (1st.) evaluated as moderately polluted, Zn (6st.) evaluated as LEL when compared with sediment quality standard of USEPA and Ontario sediment quality guidelines. Most heavy metals contents were I levels that dose not affected the benthos when compared with sediment pollution evaluation standard of NIER. The results of EX, EF, Igeo and CF showed the contents of Zn, Pb and Cd exceed the background contents and distributing of anthropogenic pollution and evaluated as moderately polluted level. And Nm-08 were relatively high level of contamination in the study area. However as results of PLI (less than 1), all sampling sites were evaluated unpolluted level.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5C
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• pp.209-218
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• 2010

In residual soils, large particles such as rock fragments or gravel are surrounded by sand or clay. The strength of such granular mixtures can be controlled by the concentration of fine or coarse grains. The percentage by weight, size or shape of gravel in the mixture that can control the strength of the mixture has not been clearly determined for various granular mixtures. In this study, the effect of dispersed gravels on the shear characteristics of sand was evaluated. Large and small gravels were inserted in the middle of each layer with moist Nakdong River sand and compacted into a cylindrical sample with five equal layers. Embedded gravel ratios by weight were 0, 3, 9, and 14%. After consolidation, a series of undrained triaxial compression tests was performed on Nakdong River sand with dispersed gravels. Maximum deviator stresses of the Nakdong River sand with large gravels decrease up to 38% as a percentage of embedded gravels increases. Such strength degradation decreases as a confining pressure increases. The maximum deviator stress increases as the percentage by weight of small gravel increases; at 3 or 9% of gravel weight it slightly increases but at 14% of gravel weight it increases up to 34%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3C
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• pp.93-102
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• 2011

Most experimental studies on soil liquefaction are related to clean sands. However, soils in the field or reclaimed grounds commonly contain some amounts of silt and clay rather than clean sand only. Many researchers investigated the effect of fine contents on liquefaction resistance and mainly used non-plastic fines such as silts. In this study, 10% of plastic fines with various plasticity index (PI) such as 8, 18, 50, and 377 were mixed with wet Nakdong River sand and then loose, medium, and dense specimens were prepared by undercompaction method. A series of undrained cyclic triaxial tests were carried out by applying three different cyclic stress ratios. As a result, the liquefaction resistance tended to decrease as a PI of fines in the specimens with equal fine content increased. On the other hand, the difference between loose specimens with low and high plasticity fines was not clearly observed in terms of liquefaction resistance. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as a plasticity of fines increased.

• Journal of the Korean Geotechnical Society
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• v.33 no.1
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• pp.57-65
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• 2017

During a construction of embankment, sub base, or retaining wall backfill, the speedy measurement of water content is necessary. In this study, a test method for field determination of water content of soil by the calcium carbide gas pressure (speedy water content measurement method) was evaluated for its reliability and accuracy. Dry oven and microwave oven methods were also used for water content measurement. In the test, weathered granite and Nakdong River sand in the site and kaolinite were used for water content measurement. The mass of 20, 22, 24, 26, 28, and 30 g of soil was respectively tested for 1, 3, and 5 min. The effect of each sample on water content was compared one another and analyzed. As the mass and testing time increased, the water content increased. The amount of soil was more important factor than testing time for the speedy water content measurement. In order to obtain similar result to that of dry oven method, 3 min of testing time with 24 g of soil was necessary for weathered granite classified as SM and 3 min with 30 g for Nakdong River sand classified as SP. For Nakdong River sand with 20-50% of kaolinite, the water content by speedy measurement increased as the clay content increased.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.6
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• pp.444-452
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• 2009

Textural parameters were calculated from the surface sediments collected from Jinu-do beach in Nov. 2005 and May 2006. In Nov. 2005 and May, 2006, the grain size distribution of surface sediments shows that the mode of $3.0\phi$(i.e., 0.125 mm) dominated the west beach of Jinu-do, but in the east beach the mode of $3.0\phi$(i.e., 0.125 mm) decreased and the mode of $2.5\phi$(i.e., 0.177 mm) was apparently distinct, resulting in the more coarsening trend. Mean grain size of surface sediments also indicates little difference in the west beach between two investigations, but the increasing difference between mean grain sizes in the east beach, showing more coarsening pattern. Such seasonal pattern corresponds to the positive skewness in the east beach in May, 2006. As a result, after the winter in 2005, the surface sediments in the west beach of Jinu-do experienced a little variation, whereas the apparent coarsening of surface sediments occurred in the east beach by removal of $3.0\phi$(i.e., 0.125 mm) fine-grained sand particles. The observed seasonal change may be attributed to the different hydrographic condition and sediment delivery/removal on the surface sediments between the west beach and the east beach of Jinu-do through the increased precipitation and more freshwater discharge from the Nakdong River during the summer and the intensified wave and tide during the winter in the Nakdong River estuary.

• Journal of Environmental Science International
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• v.16 no.10
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• pp.1157-1167
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• 2007

In an effort to interpret the characteristics of fine particle concentrations in Busan, time variations of hourly monitored concentrations $PM_{10}$ (Particulate Matter with aerodynamic Diameter ${\le}10\;{\mu}m$) in Busan are analyzed for the period from 2000 to 2005. The characteristics of aerosol second generation formation process is also interpreted qualitatively, by using the statistical analysis of the meteorological variables including temperature, wind speed, and relative humidity. The result shows some significant annual, seasonal, weekly and diurnal variations of $PM_{10}$ concentrations. In particular, seasonal(i.e., spring) variations are governed by frequency of yellow sand events even for the non-yellow sand cases where yellow-sand days are eliminated in our analysis. However, in seasonal variation, summer season predominate lower $PM_{10}$ concentrations due to the frequent precipitation, and weekly and diurnal variations are both found to be reflecting the emission rate from traffic amount. Correlation coefficients between $PM_{10}$ concentration and meterological variables for non-yellow sand days show overall negative correlation with visibility, wind speed, cloud amounts, and relative humidity. However for non-precipitation days, during non-yellow sand period positive correlation are found clearly with relative humidity, suggesting the importance of secondary aerosol formation in Busan that can be achieved by both homogeneous aerosol formation and heterogeneous transformations resulting from hygroscopic aerosol characteristics.

• Environmental Engineering Research
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• v.18 no.3
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• pp.129-137
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• 2013

The infiltration of rainwater into the surface soil is highly dependent on hydraulic variables, such as the infiltration rate, capillary fringe, moisture content, and unsaturated/saturated hydraulic conductivity. This study estimates the hydraulic conductivity (K) of fluvial deposits at three sites on the right and left banks of Nakdong River in Gyeongbuk Province, South Korea, including the Gumi, Waegwan, and Seongju bridge sites. The K values of 80 samples from 13 boreholes were estimated by using six grain-size methods (Hazen, Slichter, Kozeny, Beyer, Sauerbrei, and Pavchich formulae). The Beyer, Hazen, and Slichter methods showed a better relationship with K values along with an effective grain size than did the other three methods. The grain-size, pumping test, and slug test analyses resulted in different K values, but with similar K values in the grain-size analysis and pumping test. The lower K values of the slug test represent the uppermost fine sand layer.

• Journal of Korea Water Resources Association
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• v.56 no.9
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• pp.553-562
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• 2023

The Gobiobotia naktongensis is a species endemic to Korea, and it has recently been designated as a class I endangered species of freshwater fish. Naeseong Stream, one of the tributaries of the Nakdong River, where the Gobiobotia naktongensis was first discovered, provided an optimal habitat for the Gobiobotia naktongensis in the past with fine sand beds and riffle. Currently, due to the construction of Yeongju Dam and the excessive dredging of river channels by the local government, the riverbed armoring in the downstream area of the dam is undergoing rapid changes, and as a result, the habitat environment of the Gobiobotia naktongensis is deteriorating. In this study, the variations of the habitat suitability of the Gobiobotia naktongensis due to the change in the riverbed grain size of the Naeseong Stream were analyzed based on the WUA (weight usable area) using the physical habitat model, River2D. The study domain is the reach from Seoktap Bridge to Hoeryong Bridge downstream of Yeongju Dam. The change in riverbed grain size was analyzed using D50 acquired in 2010 and 2020, respectively. The substrate grain size of Naeseong Stream in 2020 was thicker than that in 2010, and the riverbed coarsening phenomenon was evident overall. As a result of the River2D analysis, the area in which the Gobiobotia naktongensis could inhabit was only about 0.75% in 2010 compared to the entire area of the flow, and even this decreased to 0.55% in 2020 due to riverbed armoring.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.312-322
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• 1999

We have studied both submarine morphology and sediment characteristics of waste disposal sites in the southwestern Ulleung Basin, East Sea, as part of a marine environmental preservation program. The Jung waste disposal site in the outer shelf is characterized by the thick accumulation of coarse-grained palimpsest sediments and fine-grained sediments from various sources. The Byung waste disposal site in the continental slope is generally characterized by hemipelagic muds with intermittent sandy sediments originated from the outer shelf and upper slope. The hemipelagic sediments, draping the seafloor, consist of fluidized muds. The core sediments show numerous bioturbation structures which cause vertical mixing of sediments. The surface sediments can be divided into four sand types (S-1, S-2, S-3, and S-4) and two mud types (M-1 and M-2) based on relative contents of reworked coarse-grained palimpsest sediments and fine-grained sediments. sorting and heavy mineral contents. The sands are probably relict sediments reworked during high-energy conditions such as typoon or storm. On the other hand, the muds were originated from various sources such as recent input from the Nakdong River, reworked fine-grained sediment from the shelf or suspended particulate matter from the East Sea Warm Current.