• Journal of the Korean Geotechnical Society
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• v.36 no.10
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• pp.5-19
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• 2020

With increasing demand for offshore structures, the demand for temporary structures to help the offshore construction work has increased. A cofferdam is a temporary barrier to stop the inflow of water in the construction site and allows working in the dry condition when the construction is done within the water. However, it is a major cause of construction delays and increased costs because additional works are required to block the water inflow. Recently, in order to overcome the limitations of the conventional cofferdam methods and to increase economic efficiency, a large-diameter steel cofferdam method has been proposed which can be installed quickly in the seabed by using the suction pressure. In this circular steel cofferdam method, the top side of the cofferdam including the top-lid is always exposed above the sea level in order to use it as a water barrier, unlike the conventional suction bucket foundation. After installation, the top-lid of the cofferdam is removed and the water filled inside the cofferdam is discharged to make the interior dry condition. In this study, the circular steel cofferdam with a 5 m inner diameter was fabricated and the installation tests were conducted at the Saemaguem test site. During the experiment, variation of suction pressure, leakage between connections, structure deformation, and inclination of the steel cofferdam were measured and post-analyzed. This study verified the new circular steel cofferdam method and confirmed that the suction installation method can be successfully used for various purposes on offshore structures.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.243-249
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• 2000

Seasonal variation in species composition and abundance of shallow water fish off Yongwon, Jinhae in the southern coast of Korea was determined by the analysis of monthly samples collected by a beach seine from January to December, 1998. Among 54 species identified, the resident species such as Favonigobius gymnauchen, Chaenogobius laevis, Pholis nebulosa and juvenile Hyporhamphus intermedius were predominated in abundance. The temporal species such as Sardinella zunasi, Leiognathus nuchalis and Takifugu niphobles were collected between April and September. Mean abundance (322 individuals/1000 $m^2$ or 806 g/1000 $m^2$) was higher than that in the shallow sand surf zone of Teachon, but lower than that in the shallow mud area of Chonsu Bay in the western coast of Korea. A large number of H. intermedius were collected in cold months between November and January. The dominant resident species began to be collected from february, and the number of species and biomass were increased until July. A small number of temporal species were collected and subsequently the abundance was low from August to October when high abundance was expected as in the other shallow waters by recruitment of a large number of juveniles of temporal species. The low abundance in these warm months seemed to be related to the water quality by weak water circulation in this shallow mud area.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.536-544
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• 2016

Recently, with the increase in the number of high rise and huge scaled buildings, ultra-high strength concrete with 80~100 MPa has been used increasingly to withstand excessive loads. Among the components of concrete, the effects of the kinds and properties of fine aggregates on the performance and economic advantages of ultra-high strength concrete need to be evaluated carefully. Therefore, this study examined the effects of the type of fine aggregates and mixing methods on the engineering properties of ultra-high strength concrete by varying the fine aggregates including limestone fine aggregate (LFA), electrical arc slag fine aggregate (EFA), washed sea sand (SFA), and granite fine aggregate (GFA) and their mixtures. Ultra-high strength concrete was fabricated with a 20 % water to binder ratio (W/B) and incorporated with 70 % of Ordinary Portland cement: 20 % of fly ash:10 % silica fume. The test results indicate that for a given superplasticizer dose, the use of LFA resulted in increases in slump flow and L-flow compared to the mixtures using other aggregates due to the improved particle shape and grading of LFA. In addition, the use of LFA and EFA led to enhanced compressive strength and a decrease in autogenous shrinkage due to the improved elastic properties of LFA and the presence of free-CaO in EFA, which resulted in the formation of C-S-H.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.6
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• pp.377-383
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• 2000

The composition of primary minerals of sand fractions and secondary minerals of clay fractions were investigated on the polder soils developed from alluvio-marine deposits near to Sapgyo-lake, constructed a sea dike across river estuary located in the west coast. The effects of a topographical sequence on the physico-chemical properties and mineralogical characteristics were evaluated using XRD, DTA, and TG with the chemical composition of $H^+$ saturated clays. Soils located on the seashore side were more silt fraction, higher pH and exchangeable cations than the others. The dominant minerals of soil parent materials are in the order of quartz, feldspars, micas, chlorite and amphibole. According to the greater distance from the lake, the amount of 1:1 minerals increased, but 2:1 minerals decreased. The dominant clay minerals of polder soils are kaolinite, vermiculite and illite. Hydroxy interlayer minerals are abundant in the clay fractions derived from the soil parent materials which have relatively low soil pH.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.190-200
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• 2001

An ecological study was performed to investigate the community structure of the benthic macrofaunal assemblage on the Cheokjeon tidal flat, Incheon, Korea. Benthic samples were collected between Sept. 1990 and July1992 at three stations to compare environmental factors with the structure of benthic community among station sand seasons. Overall, macrofauna comprised a total of 111 species, and the mean density (708.1 md./$m^2$) and biomass (214.9gWWt/$m^2$). The number of species and individuals of polychaetes, molluscs and crustaceans made up more than 80% of the total number. On the other hand, in terms of biomass, bivalves and holothuroideans indicated that they were the dominant faunal groups. Hierarchical classification using the Bray-Curtis coefficient categorized samples into 3 station and 4 faunal groups. In terms of q-mode, there consisted of upper, middle and low tidal flat stations, respectively. And four faunistic groups were established as follows: 1) Heteromastus filifomis-Mactra veneriformis-Solen strictus-Ilyoplax finggi (wide-ranging elevation specialists), 2)Nephtys chemulpoensis-Macrophthalmus gaponicus (high elevation specialists), 3) Glycera subaenea-Decorifer matusimana-Tritodynamia (middle elevation specialists) and 4) Nephtys polybranchia-Borniopsis tsurumaru-Asthenognathus inaequipes-Protankyra bidentata (low elevation Specialists).

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.3
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• pp.122-130
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• 2013

To examine floc characteristics of cohesive bed sediment of the Yeongsan River estuary, a floc camera system has been developed and utilized to observe flocs under varying conditions. In order to validate the floc camera system, sand particles were passed through 88-125 and $63-88{\mu}m$ sieves and observed within the laboratory. Mean grain size and settling velocities were found to be 102 and $56.2{\mu}m$ and 6.7 and 5.9 mm/s, respectively. Artifacts of particles estimated outside of the sieve range are attributed to being imaged out of the depth of focus. However, as mean grain size and settling velocity of each size class were within the confidence interval, the floc camera system was confidently used to examine cohesive bed sediments of Yeongsan River estuary. The bed sediment sample was prepared with a concentration of 0.1 g/L in 0 psu deionized water. The mean grain size, settling velocity and fractal dimension of flocs were $40.6{\pm}0.66{\mu}m$, 14 mm/s, and 2.86, respectively. Experiments were also conducted using different salinities (10 and 34 psu) and sediment concentrations (0.1 and 0.3 g/L). Despite changing these parameters, the mean observed grain size and settling velocities were found to be the same within the error range of the system. The relatively higher values of settling velocity and fractal dimension are considered a result of the sediment containing relatively small concentrations of organic matter. Moreover, consistent floc size over various grain sizes and concentrations may be the result of insufficient turbulence to aggregate flocs.

• Economic and Environmental Geology
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• v.48 no.5
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• pp.379-390
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• 2015

Multibeam backscatter strength is dependent not only on seafloor sediment facies but also on changed incidence angle due to the actual bottom slope. Therefore, the correction for actual bottom slope should be considered before the analysis of backscatter strength. This paper demonstrates the backscatter correction technique for the actual incidence angle and ensonified area. The target area is a part of the eastern Yellow Sea with water depths of 46~55 m. The area is located between the sand ridges and covered by large dunes with various bottom slopes. The dunes usually have the gentle slopes of about $1{\sim}3^{\circ}$, but show some steep slopes of $5{\sim}15^{\circ}$ on the crest. The backscatter strength values on the crest range from -34 to -23 dB, assuming that the bottom is flat. However, this study shows that the backscatter strength range was somewhat reduced (-32~-25 dB) after correction for actual bottom slope. In addition, the backscatter imagery was significantly improved; high and low backscatter strength values on the crest due to the actual bottom slope were normalized. The results demonstrate that the correction technique in this study is an effective tool for processing backscatter strength.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.3
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• pp.224-235
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• 2014

Changes in the interactions among incident ocean water waves, coastal debris (marine debris), and the back vegetation zone line on a natural sandy beach on the island of Jinu-do in the Nakdong river estuary were investigated. The study involved a cross-sectional field survey of the beach, numerical modeling of incident ocean water waves, field observations of the distribution of coastal debris, and vegetation zone line tracking using GPS. The conclusions of this study can be summarized as follows: (1) The ground level of the swash zone (sandy beach) on Jinu-do is rising, and the vegetation zone line, which is the boundary of the coastal sand dunes, shows a tendency to move forward toward the open sea. The vegetation zone line is developing particularly strongly in the offshore direction in areas where the ground level is elevated by more than 1.5 m. (2) The spatial distributions of incident waves differed due to variations in the water depth at the front of the beach, and the wave run-up in the swash zone also displayed complex spatial variations. With a large wave run-up, coastal debris may reach the vegetation zone line, but if the run-up is smaller, coastal debris is more likely to deposit in the form of an independent island on the beach. The deposited coastal debris can then become a factor determining which vegetation zone line advances or retreats. Finally, based on the results of this investigation, a schematic concept of the mechanisms of interaction between the coastal debris and the coastal vegetation zone line due to wave action was derived.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.207-212
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• 2008

Bathymetry, side scan sonar, and magnetic survey data for the summit area of Dokdo obtained by Korea Ocean Research & Development Institute in 1999, 2004, and 2007 were analyzed to investigate the geophysical characteristics of the summit. Bathymetry and topographic data for the summit of Dokdo show uneven seabed and irregular undulations from costal line to -90 m in water depth, indicating the effects of partial erosions and taluses. The stepped slope in the bathymetry is supposed to be a coastal terrace suggesting repetition of transgressions and regressions in the Quaternary. The bathymetry and the side scan sonar data show a small crater, assumed to be formed by post volcanisms, at depth of $-100\;{\sim}\;-120\;m$ in the northeastern and the northwestern parts of the survey area. Except some areas with shallow sand sedimentary deposits, there are rocky seafloor and lack of sediments in the side scan sonar images of the survey area, dominantly. The analytic signal of the magnetic anomaly coincides with other geophysical results regarding to the location of the residual crater. The geophysical constraints of the summit of Dokdo propose that the islets and the rocky seabed elongated northeastward and northwestward from the islets might be the southern crater of the Dokdo volcano.

• Korean Journal of Plant Resources
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• v.23 no.4
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• pp.261-273
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• 2010

This study intended to investigate the environmental factors including soil and vegetation in order to understand the environmental and ecological characteristics of seven different habitats of Viola websteri. These habitats, according to investigations, are mostly located on the slope of mountains facing north at an altitude of 343 m to 991 m above sea level with angle of inclination from 1 degree to 33 degrees. The type of soil is mostly sandy loam and the average field capacity of soil is 28.97%. Their average organic matter is 16.63%, soil pH 5.62, and available phosphorus is 14.75%. A total of 133 vascular plants are identified in 18 quadrates of seven habitats. Dominant species of woody plants in seven habitats are represented as Acer pictum subsp. mono and Quercus mongolica in tree layer, and Acer pictum subsp. mono in subtree layer. Importance value of Viola websteri is 9.66%, as regards the herbaceous layer, and five highly ranked species such as Meehania urticifolia(8.53%), Pseudostellaria heterophylla(6.51%), Hylomecon vernalis(5.15%), Oxalis obtriangulata (4.52%), and Pseudostellaria davidii(4.15%) are considered to be an affinity with Viola websteri in their habitats. The degree of their average species diversity is 1.32, and that of dominance and evenness are 0.08 and 0.89, respectively. Correlation coefficients analysis based on environmental factors, vegetation and soil analysis shows that the coverage of Viola websteri is correlated with silt and sand ratio, and coverage of tree layers are correlated with species richness and altitude. Cluster analysis based on vegetation structure of each habitats are forms a three groups.