• Journal of Wetlands Research
• /
• v.15 no.2
• /
• pp.281-288
• /
• 2013

In this study we estimated the carrying capacity of the southern intertidal zone of Kanghwa Island to evaluate the habitat quality for Curlews(Far Eastern Curlew Numenius madagascariensis and Eurasian Curlew Numenius arquata). Biomass of the macroinvertebrate(Macrophthalmus japonicus) was estimated by based on the spatial distribution of the sediment grain size using GIS tools. According to our analysis the southern intertidal zone of Kanghwa Island was able to support 11,767 individuals for 153 days in the Spring 2012 and 16,275 individuals for 122 days in the Autumn 2012. The proportion of mean population to the carrying capacity in the Spring and Autumn was 9.4% and 5.9%, respectively. These values are 2.8-6.3% smaller than those of the previous study held in 1993-94. For the conservation of the study area, more research and management is needed. And in further studies, diverse characteristics of the intertidal habitat should be considered in spatial analysis to have a precise estimate of the carrying capacity.

• Journal of the Korean Ceramic Society
• /
• v.37 no.2
• /
• pp.186-193
• /
• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.

• Journal of the Korean GEO-environmental Society
• /
• v.4 no.1
• /
• pp.49-58
• /
• 2003

The suction of unsaturated soil is one of the important variables to influence on volume change behavior. This research was performed to analyze the soil-water characteristic of decomposed granite soils in Chung Cheong area, and showed relationship with grain-size distribution. Empirical parameters a, n, m are main variables that can be used in the empirical equations in order to predict unsaturated soil. Decomposed granite soils is taken at 12 field, and redistributed due to a, n, m parameters. The result of Extractor test is showed that matric suction is effected by the grain-size distribution curve's left-right location, degree of an angle and fine contents of a soil.

• Geotechnical Engineering
• /
• v.12 no.1
• /
• pp.63-72
• /
• 1996

The current practice in construction of reinforced earth retaining walls is to use a granular soil for the backfill material. When the material is available in site, the construetion cost can be remarkably reduced. As the weathered granite soils are abundant and widely distributed throughout the Korean peninsula: whether they are suitable or not as the backfill material is considered to be the most important key in economic construction of the wall. This paper investigates the grain size distribution of the weathered soils which locate at many places throughout the nation and then examines limitation of their use based on the specifications of different countries. The variaton of shear strength with both different fine contents and saturation is also investigated. It is known that the grain size distribution of most weathered soils are not satisfied with the general requirement. However their use is possible in wide range when the backfill keeps in unsaturated condition using good drainage facilities and 1 or pervious reinforcements.

• Korean Journal of Metals and Materials
• /
• v.49 no.6
• /
• pp.474-487
• /
• 2011

Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route $B_c$, and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.

• Journal of the Korean GEO-environmental Society
• /
• v.23 no.5
• /
• pp.15-24
• /
• 2022

In order to improve dredged area, long time and high cost is needed because of bad engineering and physical conditions. And there is no suitable example of pipe mixing method at domestic site. Moreover, applicability and effectiveness of this method is uncertain and shows different results between site and laboratory test. In order to solve these problems, we determined proper grain size distribution and water content range using dredged soil and reformed material (standard sand & material controlling grain size distribution) in the laboratory test. As a result, we confirmed that coefficient of sediment consolidation is increased and there is an improvement about separation sedimentation. Undrained shear strength was derived by water content of reformed dredging soil through regression analysis of test results. We suggest the correlation equation for determining mixing ratio.

• 한국해양학회지
• /
• v.27 no.4
• /
• pp.277-289
• /
• 1992

Kyeonggi Bay, a macrotidal coastal embayment in the Yellow Sea coast of central korea, is fringed by vastly developed tidal flats. About 400 surface sediment samples were collected from the intertidal and subtidal zones of Kyeonggi Bay for a study of the sediment distribution pattern and the surface sediment characteristics of this environment. The kyeonggi Bay surface sediment becomes progressively finer in the shoreward direction, from offshore sand to shoreward silty sand and sandy silt. This shoreward-fining trend is repeated again on the tidal flat and, as a consequence, a grain-size break occurs near the low-water line which separates the intertidal area from the subtidal one. The intertidal and subtidal sediments differ from each other in textural characteristics such as mean grain size and skewness and this can be interpreted to result from differences in hydraulic energy and morphology between the two environments. The mineral and chemical compositions of the Kyeonggi Bay sediments are largely controlled by the sediment grain size. Smectite was nearly absent in the clay mineral assemblage of Kyeonggi Bay sediment. The contents of Co, Cu and Ni were high in the Banweol tidal flat, which suggests a continuous process of accumulation of these metals. the intertidal environment appears to respond rapidly to artificial coastal modifications, the effects of which should be taken into consideration when planning a dam construction or coastal reclamation.

• Analytical Science and Technology
• /
• v.27 no.1
• /
• pp.11-21
• /
• 2014

An investigation of grain size, organic compounds and metal distribution in 23 sediment samples of the Geum-River basin (Korea) was conducted in two seasons of 2012 (dry season and rainy season). The samples of sediment were collected from the basin and investigated for concentrations of some metal and general indexes containing grain size. Concentrations of Pb, Zn, Cu, Cr, Ni, As, Cd, Hg, Al and Li have been determined by inductively coupled plasma spectrometer (ICP) and the sediments organic matter content was determined by the loss on ignition, and sediments were fractionated with three different nylon sieves. Correlation analysis was made for grain size, organic material and metal concentrations, and the Pearson correlation coefficients between their concentrations were determined. As a result, the higher metal concentrations were found in the period of the dry season than in another season. The metal concentrations showed high correlation with that of organic material (COD and TOC). Thereby, the high distribution of metal concentrations in sediment containing high organic compound is suggesting an interaction with organic matter.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.13 no.3
• /
• pp.198-205
• /
• 2010

The purpose of this study is to investigate the characteristics of the grain size distribution and organic matters to understand the current status of the tidal flat sediment for efficient management of Suncheon Bay. We investigated the characteristics of the surface sediments in the mouth area of the Suncheon Bay at fifteen stations in April and July, 2009. Specific conclusions were as follows. The sediments in the most part of tidal flat was shown as muddy facies(clay and silt contents was more than 90%), whereas in the tidal river affected by water flow from the Dongstream was shown as sandy facies. The analyzed values of the tidal flat sediment were in the range of $1.9{\sim}3.8{\phi}$(mean $2.5{\phi}$) for sorting, and -1.5~3.2(mean -0.3) for skewness, and 1.5~14.1(mean 3.9) for kurtosis. So we knew that the tidal flat sediments in the Suncheon Bay was mainly composed by fine-grained sediment. Erosion was happened in the tidal river, whereas sedimentation was occurred in the tidal flat. The most of organic matters was derived from the Dongstream. Total organic matters shown as ignition loss was 5.75%, COD and $H_2S$ values were lower than the eutrophication level(COD; 20.0 mg/g dry, $H_2S$; 0.2 mg S/g dry). From our research the tidal flat of the Suncheon Bay is relatively fine, but a part of the flat was exceed the environmental standard. So we have to establish effective countermeasures to reduce the organic matters and nutrients derived from stream for environmental preservation of the Suncheon bay and conduct scientifically sustainable monitering for streams flowing into Suncheon Bay and tidal flat.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.27 no.2
• /
• pp.57-71
• /
• 1985

The characteristics of compaction and unconfined compressive strength were investigated by mixing with lime to all soils adjusted by given percentages of two kinds of clays to sand to obtain the most effective distribution of grain size and the optimum lime content for soil stabilization. In addition, unconfined compressive strength and durability tested by adding of sodium metasilicate, sodium sulfate, sodium carbonate, sodium gydroxide and magnesium oxide to lime-soil mixture mixed with 8 percent lime to adjusted soil having the mixing percentage of 60 percent of cohesive black clay and 40 percent of sand by weight to get the effect and the optimum content of chemicals. The results obtained were as follows; 1.With the addition of more lime, the optimum moisture content was increased, and the maximum dry density was decreased, whereas the more the amount of clay and the less was the maximum drt density. 2. In the soil having more fine grain size the unconfined compressive strength was larger in the earlier stage of curing period, in accordance with the longer period, the mixing percentages of sand to clay showing the maximum unconfined compressive strength, on the basis of 28-day strength, were 60% : 40% (black clay) and 40% : 60% (brown clay) respectively. 3. The reason why the soil adjusted with black clay was remarkably bigger in the unconfined compressive strength than ones adjusted with brown clay for all specimen of lime-soil mixture was the difference in the kind of clay, the amount of chemical compositions the value of pH. Black clay was mainly composed of halloysite that reacted with lime satisfactorily, whereas the main composition of brown clay was kaolinite that was less effect in the enhance of unconfined compressive strength. Also the difference of unconfined compressive strength was because black clay was larger in the amount of composition of calcium oxide and magnesium oxide in the value of pH affecting directly on the unconfined compressive strength of lime-soil mixture than brown clay. 4. In the lime-soil mixture mixed with 8 percent of lime to soil that mixing percentage of sand to black clay was 60% : 40%, on the standard of 7-day strength, the effect of chemical was arranged in the order of magnesium oxide, sodium carbonate, sodium sulfate, sodium hydroxide and sodium metasilicate. 5. The optimum amount of chemical being applicable to the maximum unconfined compressive strength of lime-chemical-soil mixture was 1 percent by weight for air dry soil in the case of adding sodium carbonated and 0.75 percent on sodium hydroxide, the unconfined compressive strength was increased continuously with increase of the amount of chemical up to 2 percent of chemical content is the lime-chemical-soil mixture added sodium metasilicate, sodium sulfate and magnesium oxide. 6. It was considered that the chemical played and accelerant role of early revelation of strength because the rate of increase of unconfined compressive strength of all of lime-chemical-soil mixtures was largest on the 7-day cured specimen. 7. The effect of test on freezing and thawing after adding suitable amount of chemical on the lime-soil mixture mixed with 8 percent of lime to soil that mixing percentage of sand to black clay was 60% : 40% was arranged in the order of magnesium oxide, sodium carbonate, sodium sulfate, sodium metasilicate and sodium hydroxide.