• Journal of Korea Water Resources Association
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• v.51 no.12
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• pp.1273-1284
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• 2018

The flow and bed change were analyzed using the CCHE2D model, which is a two-dimensional numerical model, at a confluence of the Namhan River and Seom River where deposition occurs predominantly after the "Four Major Rivers Restoration Project." The characteristic of the junction is that the tributary of Seom River joined into the curved channel of the main reach of the Namhan River. The CCHE2D model analyzes the non-equilibrium sediment transport, and the adaptation lengths for the bed load and suspended load are important variables in the model. At the target area, the adaptation length for the bed load showed the greatest influence on the river bed change. Numerical simulation results demonstrated that the discharge ratio ($Q_r$) change affected the flow and bed change in the Namhan River and Seom river junction. When $Q_r{\leq}2.5$, the flow velocity of the main reach increased before confluence, thereby reducing the flow separation zone and decreasing the deposition inside the junction. When $Q_r$>2.5, there was a high possibility that deposition would be increased, thereby forming sand bar. Numerical simulation showed that a fixed sand bar has been formed at the junction due to the change of discharge ratio, which occurred in 2013.

• Journal of The Geomorphological Association of Korea
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• v.18 no.4
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• pp.223-233
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• 2011

The aims of this study is about distribution characteristics of tidal coastal landforms, and that changing process in the Hampyeung Bay, which has a semi-enclosed bay like basin shape without inflow of stream, the mouth of open sea is narrow and forms with wide ends toward inland sea. The source of deposits are moved materials by tidal currents and from coastal slopes. Main landform elements of study area consist of tidal flat, tidal channels, intertidal sand bar, sea cliffs, and sea terrace. Tidal flats is classified with mud flat and mixed flat by grain size composition. Mud flats have developed at the shoreline area that tidal flat is closed to the continuity of gentle slope, and mixed flat developed at the foot of the sea cliffs and sea terraces. Quaternary deposits were identified in the coastal materials sedimented by the sea-level change. According to the analysis of grain size composition during last ten years, sands and silt has increased 2% and 6% respectively, clay has been decreased by 9%. The concaved tidal flats are colonized by salt plants. Areal changes of salt plants expanded near four times from 2.4km² at the year 2001 to 9.3km² at the year 2009. During the same periods, mean grain size became coarser from 6.5φ to 4.5φ at the salt plants area.

• Ecology and Resilient Infrastructure
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• v.11 no.2
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• pp.43-54
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• 2024

Recently, most of the rivers in Korea are experiencing various problems in dimension and river environment, such as expansion of stable area where disturbance does not occur during flood, increase of excessive trees in river channel, fixation of river channel, reduction of sand bar. When the soil supplied by the flood is deposited in the river, the plant is settled in the formed terrain, and when another disturbance of the scale that does not erode there occurs after the plant is settled, the river gradually grows and the vegetation zone is formed there. In particular, in terms of river management, river forestation and river aggradation are objects that must be managed because they are disadvantageous in terms of flood control by lowering the flow rate and raising the water level. Therefore, in this study, the area of vegetation occupied by the year of sandbar was analyzed in the process of river aggradation in Jang-Hang wetland. In addition, the correlation between the growth of Jang-Hang wetland was analyzed through the analysis of the flow rate and the flooding frequency that directly affect the growth of Jang-Hang wetland. Through this, the management plan of Jang-Hang wetland, which is registered in Ramsar Wetland but has been river forestation and is undergoing river aggradation, was proposed.

• Journal of The Geomorphological Association of Korea
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• v.28 no.4
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• pp.15-30
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• 2021

This study analyzed the changes in land-cover and sedimentary environment before and after flooding through drone images and sediment analysis for the Seomjin River Chimsil Wetland. The results showed that the area of some land-covers such as sand bar, grass, and trees were continuously changed. The acidity level of the sediments in the Seomjin River Chimsil Wetland was weakened gradually by flooding and EC was also decreased. The levels of organic matter, effective phosphoric acid, and CEC, however, were fluctuating depending on branches, which seems to be the result of landization as new sedimentary environment was developed and vegetation was settled after the flood. Average mean size of river sediments was found to be fine sand, and it exhibited various particle size characteristics from granule to medium silt depending on the location. As the sedimentary environment changed due to the effects of floods and typhoons, the particles were granulated or grain refined depending on the position. In the Seomjin River Chimsil Wetland, there were factors that could interfere with geomorphic development and sedimentary environment, contamination sources in and around the wetland, and natural threat factors. Therefore, in this study, a conservation and management plan was proposed to remove these threat factors and to preserve the scarcity, naturalness, and dynamics of Seomjin River Chimsil Wetland.

• Ecology and Resilient Infrastructure
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• v.4 no.1
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• pp.3-11
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• 2017

In this study, change in vegetation on bars was analyzed using the data on hydrology and river morphology with on-site photographic monitoring data for the sites of interest of the Naeseong Stream during the period from March 2013 to July 2016 when the impoundment of Yeongju Dam began. The effect of flow condition on burial and removal of vegetation covered on bar surfaces was elucidated by comparison of on-site photographic monitoring data with continuous water level plotted with on the cross-section profile. In 2014 burial happened due to late flood, while July flood caused burial and removal in 2016. On the contrary vegetation increased in 2015 due to low flow without flood. Results of this study showing natural changes in vegetation will be reference to changes which is expected to be caused by dam impoundment.

• Geotechnical Engineering
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• v.13 no.4
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• pp.55-66
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• 1997

In order to investigate the influence of installation angle of reticulated root piles(RRP) on their lateral load capacities, model tests of lateral loads on RRP with various installation angles $0^{\circ}\;, 5^{\circ}\;, 10^{\circ}\;, 15^{\circ}\;, 20^{\circ}\;,and 25^{\circ}$ are carried out. One set of RRP consists of 12 piles which are installed in circular patterns forming two concentric circles, each of which has 6 piles. Each pile made of a steel bar of 5mm in diameter and 350mm in length, is coated with sand until the bar has the diameter of 6.5mm. According to the test results, RRP's response is travily influenced by the displacement level. At low displacement level(1m), lateral load capacity increases as the installation angle is increased. However, the value of the optimum installation angle decreases as the displacement level is increased. In fact, it is found to be $17.5^{\circ}$ at 6mm lateral displacement. The ratios of the lateral resistances for the optimum installation angles to those for the vertical RRP decrease as the lateral displacements are increased. Thus the effect of slant ins angle of RRP is expected to be reduced at higher level of lateral displacement.

• Korean Journal of Environment and Ecology
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• v.20 no.4
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• pp.374-390
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• 2006

The analysis of correlation between the 9 element (used as the classification standard of stream typology out of the 25 elements pertinent to the survey of hydromorphological structure) and both emerged benthic macroinvertebrate as well as vegetation indicated that the substrate diversity, curvature, and degree of development of the transverse bar had a high correlation with the species composition. Only COD concentration was found to have the statistically significant correlation with the distribution of benthos among the 12 aquatic and chemical elements. Specifically, the analysis of the biotic and abiotic factors in this study indicated that there was a statistically significant correlation between the sand river and cobble river in the positive(+) and negative(-) aspects, suggesting that there is a distinctive difference between the two types of rivers in terms of hydromorphologlcal structure and ecological characteristics. Therefore, the findings of this study imply that the consideration of a biotop is prerequisite for the evaluation of stream status regarding stream restoration or the ecological topology of streams.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.1
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• pp.101-109
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• 2008

Several numerical models for predicting beach profile changes have been developed by many researchers. Many of the earlier models are known to simulate the erosional profiles with the formation of offshore bar. However, most of the models don't have proper mechanism to incorporate the recovery process of the eroded profiles after a storm and can not simulate the beach accretion with acceptable accuracy. In order to overcome these shortcomings, we propose a new numerical model which has new features to simulate the accretional phase of beach recovery process after storm including such as redistribution of suspended sand particles near the breaking point. The simulation results of the proposed model were compared with LWT (Large Wave Tank) experiments performed at CRIEPI (Central Research Institute of Electric Power Industry in Japan) and CE (the Us Army Corps of Engineers) and it was shown to have performed better compared to SBEACH (Storm-induced BEAch CHange).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.3 no.2
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• pp.80-83
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• 2002

The effect of chloride content on the corrosion of reinforced bar in concrete was studied. The mixing ratio of the concrete was 1 : 1.78 : 5.35 : 4.73 (water : content : ballast : sand). The studied chloride content was in the range of 0∼3.5 wt%. The corrosion potentials were measured in every week for two years. The copper-copper sulfate electrode (CSE) was employed as a reference electrode. After two years, the corroded structure was examined and compared to measured corrosion potential. Any visible difference was founded in the specimen located indoor and outdoor. The chloride concentration enhanced rusting and reinforced bar, shifting the potential to active range. The results showed good argument with Van daveer criteria. In 3.5 wt% chloride, the potential shifted belong -350 mV after 58week. Specimen in 1.75 wt% chloride, showed the potential between -200 mV∼-350 mV. However those in free chloride solution maintained above -200 mV for the studied period. It can the concluded that the chloride enhanced corrosion of rebar in concrete and the electrochemical potential can be a promising corrosion monitoring technique.

• Journal of the Korean Geotechnical Society
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• v.35 no.12
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• pp.69-89
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• 2019

Design chart solution and table solution were proposed by Choi et al. (2019a), which conducted a parametric numerical study for the bored PHC piles socketed into weathered rocks through sandy soil layers. Based on the Choi et al. (2019a), the new prediction formulae for mobilized capacity components such as total capacity, total skin friction and skin friction of sand at the settlement of 5% pile diameter were proposed in this study. The proposed prediction formulae (EQ-G1) considers pile diameter, relative embedment length and ${\bar{N}}$ (i.e, corrected N) value and their verification results are as follows. The SRF calculated from the new proposed design method was 71~94%, which are greatly improved compared with results by the existing design method. The design efficiency of bearing capacity was in the range of reasonable design except 4 cases, and the design efficiency of the PHC pile was evaluated as 85%. Therefore, it is possible that allowable compressive load (P_all) of PHC pile can be utilized in the resonable design by means of the new proposed method using EQ-G1 equations. And the other new proposed equations of EQ-G2-3 can be utilized approximately in calculation of axial compressive bearing capacity components for prebored PHC pile.