• The Korean Journal of Ecology
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• v.25 no.5
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• pp.305-313
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• 2002

The physico-chemical characteristics of water and sediment, and structures of vegetation of the vascular hydrophytes were investigated in the West Nakdong River. Water quality was eutrophic according to the mean values and the ranges of water properties such as pH, DO, BOD, chlorophyll a, total nitrogen and phosphate, and other nutrients. A few cases were hypereutrophic for chlorophyll a level in summer. Soil reaction was weak acid. Composition of sediment was mainly sand except in SI(Sinan chideung) of which was mainly clay, and SU(Suan chideung) of which was mainly silt. Flora of vascular hydrophyte had 26 species and 1 variety comprising 16 families. Trapa japonica was dominant species in the sites of DU(Dunchido), GA(Garak chideung) and SU. Nymphoides peltata and Hydrocharis dubia dominated in DA and SI, respectively. Species diversity and evenness were relatively high in SI and SU but dominance was high in DA. After June, water lettuce(Pistia stratiotes) and water hyacinth(Eichhornia crassipes) were flowed from tributary to the river. Standing crop of macrohydrophytes was high in DA from April to August, but it showed maximum standing crop (445g·dw/㎡) in DU after disturbance by explosive growth of exotic plants in October. In comparison with those in 1985, total productivities in DU and GA decreased to 33.5%, and the reduction ratio of dominant species, Trapa japonica was 56.7%. Najas marina, N. minor, Myriophyllum spicatum and Nymphoides indica have disappeared ever since the Nakdong barrage was constructed in the Nakdong river. They were divided into three groups (GA-SU-DU, DA, SI) by cluster analysis. Introduction of the exotic species in this river caused decreasing of endemic plants including endangered species Euryale ferox and rare species Hydocharis dubia, and food plants for waterfowl such as Trapa japonica, Vallisneria asiatica and Potamogeton crispus.

• Journal of the Korean GEO-environmental Society
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• v.7 no.4
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• pp.53-62
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• 2006

Recently, the lateral displacement of the passive piles which are installed under the revetment on the soft ground is very important during the land reclamation work along the coastal line. The revetment on the soft clay develops the lateral displacement of ground when the revetment loading exceeds a certain limit. The lateral displacement of ground causes an excessive deformation of underground structure itself and develops lateral earth pressure against the pile foundation. The subject of study is to investigate the lateral displacement of pile foundation during the construction of container terminal at the ${\bigcirc}{\bigcirc}{\bigcirc}{\bigcirc}$ port in Incheon. The displacement of pile and the vertical settlement were measured in the field and finite element method(FEM) analysis for each construction sequence was performed using AFFIMEX(Ver 3.4). From the comparison of the results from field measurement and the finite element analysis, the settlement of the reventment has already occurred at the time of field measurements. Since then, the noticeable lateral displacement of piles and settlement were occurred during the filling of dredged soil inside the revetment dredging and reclaiming work. After completing filling, the lateral displacement and field settlement were reduced remarkably. Generally, the results from the finite element analysis show larger than those from the measurement.

• Journal of the Korean Geosynthetics Society
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• v.4 no.2
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• pp.11-18
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• 2005

A pilot scale filed model test and 2-D numerical analysis was conducted to evaluate the effectiveness of constructing a geogrid-reinforced and pile-supported embankment system over soft ground to reduce differential settlement, and the results are presented hearin. Three-by-three pile groups with varying the space between pile were driven into a layer of soft marine clay and a layer of geogrid was used as reinforcement over each pile group. 2-D numerical analysis has been conducted by using the FLAC-2D(Fast Lagrangian Analysis of Continua) program for same condition of field model test. The settlement, vertical stress, and strain of geogrid due to the construction of embankment were measured at various locations. Based on the field model test and numerical analysis results, pile reinforcement generated the soil arching at the midspan of pile cap and the geogrid reinforcement helps reduce the differential settlement of the soft ground by tensile strength of geogrid. Also for $D/b{\geq}6.0$, the effectiveness of geogrid reinforcement in reducing settlement is negligible.

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.127-137
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• 2018

Gravel Compaction Pile (hereinafter referred to as GCP) is a ground improvement technique by packing crushed stones on fragile clay ground, pressing it, and forming stakes on the foundation. Although many researchers have analyzed stress behavior of GCP composite ground on domestic GCP technique using laboratory experiment and field experiment, analyses of stress behavior according to the difference of stiffness of mat foundation loaded on the upper foundation of GCP composite ground have not been done actively. Therefore, this study aimed to identify the stress concentration ratio in accordance with the difference of basis stiffness by interpreting figures. To perform this, replacement ratio was changed and modelled using ABAQUS, software for finite element analysis and analyzed the stress concentration ratio, amounts of settlement, and maximum amounts of horizontal displacement of composite ground in accordance with the difference of stiffness. An analysis showed that the stress concentration ratio of rigid foundation was highly assessed than unloading of flexible foundation in case of unloading, while amounts of settlement under flexible unloading condition were slightly higher than under rigid condition. This indicates that the characteristic of stress behavior on the different stiffness of upper foundation needs to be clarified. In addition, the maximum horizontal displacement was generated in a constant level regardless of the difference of stiffness.

• Journal of the Korean Geosynthetics Society
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• v.17 no.3
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• pp.19-32
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• 2018

Gravel Compaction Pile (GCP) method is currently being designed and constructed by empirical method because quantitative design method has not been developed, leading to various types of and frequent destruction such as expansion failure and shear failure and difficulties in establishing clear cause and developing measure to prevent destruction. In addition, despite the difference with domestic construction equipment and material characteristics, the methods applied to the overseas ground is applied to the domestic as it is, leading to remarkable difference between applied values and measured values in variables such as bearing capacity and the settlement amount. The purpose of this study was, therefore, to propose a reasonable and safe design method of GCP method by analyzing the settlement and stress behavior characteristics according to ground strength change under GCP method applied to domestic clay ground. For the purpose, settlement amount of composite ground, stress concentration ratio, and maximum horizontal displacement and expected location of GCP were analyzed using ABAQUS. The results of analysis showed that the settlement and Settlement reduction rate of composite ground decreased by more than 60% under replacement ratio of 30% or more, that the maximum horizontal displacement of GCP occurred at the depth 2.6 times pile diameter, and that the difference in horizontal displacement is slight under replacement ratio of 30%.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.285-296
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• 1999

Preloading method is used to prevent the settling of a foundation and to increase the strength of ground by consolidation settlement in advance. But, the embankment used in preloading method brings large deformation and sliding failure in the soft ground. Recently, reinforcement method is often used in embankment in order to prevent sliding failure. But, until now, the research on the stability analysis considering both the rate of strength increase of clay by embankment load and increase of resistance force by the geosynthetics in the embankment body is not found. In this study, the stability analysis program(REAP) for embankment including these two points is developed. By this program(REAP), the stability analysis can be done about during the gradual increase of embankment and the stability counterplan can be established when the safety factor is lower than allowable safety factor of design. After calculating the position of sliding failure surface, the force of geosynthetics which is selected by either the effective tensile strength or tensile force caused by the displacement of soil mass in this position is applied to stability analysis. And the increase of resisting moment can be calculated by this force. Also, the construction period can be estimated and the time for the appropriate counterplan can be decided in order to maintain the stability of embankment. And then, safe and economical embankment design can be performed.

• Journal of the Korean earth science society
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• v.36 no.3
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• pp.222-235
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• 2015

Samples were collected from both places including the coastal area within the height of 5 m above the mean sea level (msl) (DH) and the top of the coastal terrace of 10-15 m msl (KS) high in Gwangseungri, Gochanggun, Korea. To find the origin of the deposit in the coastal area, granulometric analysis and geochemical analysis were performed. The result showed that the DH samples were originated from the reddish soils overlaying weathered bedrock which presented gradual change of chemical composition from the bottom toward the top. Clay minerals were found from the DH samples. These results concluded that the DH samples were found as in-situ weathered materials. The KS samples were originated from the soil layer covering gravel layer at the foot slope of the hill along the coast. The KS samples contained different chemical compositions from the DH. It is inferred that some of this layer was disturbed or experienced the influx of foreign material. The particle size of the KS samples was different from those found on the beach. The particle size of lower parts of KS site was finer than that on the beach, but the particle size of middle part of the site was coarser than that on the beach. The sorting of the KS site was poorer than that on the beach. Thus, it is inferred that some parts of the layer were formed by short-lived high energy event rather than sustained and continuous action of tidal currents and/or waves. Analysis using an optically stimulated luminescence (OSL) method showed that the burial age of samples from KS site were found 0.65-0.71 ka. Though the characteristics of the sediment layer and forming event in this area should be further studied, it can be inferred that this sedimentary layer formed by coastal flooding with storm.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.972-976
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• 2006

비점오염은 일정한 오염원 없이 광범위한 지역에 쌓여 있는 오염물질이 강우 등에 의해 산발적으로 유출되는 비정형적인 오염을 말한다. 비점오염물질의 유출은 강우나 해빙에 의해 일시에 다량 발생되어 수계로 빠른 시간 내에 도달되게 되므로 인근 수계환경의 수질에 악영향을 미치게 되며, 이러한 오염물질을 효율적으로 처리하기 위해서는 발생원 가까이에서 수계에 도달하기 전에 저감하거나 유출과정에서 집수 처리하는 것이 가장 바람직하다. 본 연구에서는 이러한 비점오염물질의 저감을 위해 반응조를 이용한 실내실험을 실시하였다. 실내 실험장치는 아크릴로 제작 되었으며, 제원은 $1,000mm(L){\times}150mm(W){\times}300mm(H)$였다. 유입수는 시약을 이용하여 질소와 인의 농도를 고농도와 저농도로 조제하여 사용하였고, 유입은 미량 유량펌프를 이용하여 유입하였다. 토양의 오염물질의 처리 효율이 표면유출보다 하부유출에서 더 좋은 것으로 나타났기 때문에 하부유출의 양을 늘이기 위해 인위적으로 물의 흐름을 막는 정류벽을 설치한 계단형으로 구성하여 직선형과 비교하였다. 연구 결과, 단기간 저농도의 경우T-N, T-P부분에서 보면 직선형과 계단형의 표면유출 에서의 저감 효율이 T-N은 각각 -2.6 %, 2.4 %, T-P는 각각 -11.0 %, 52.9 %로 표면유출수의 오염저감효과가 개선되는 것으로 나타났다. 이는 방류벽 앞에 하부로 침투되었던 물이 표면으로 유출되면서 오염물질의 저감이 일어났기 때문으로 판단된다. 반면, 단면 및 하부유출수의 오염물질 농도는 증가한 것으로 나타났는데, 이는 토양내의 입경이 작은 silt나 clay보다 입경이 큰 모래나 자갈을 경유 하면서 오염물의 저감효과가 감소한 것으로 판단된다. 그러나 유입유량의 대부분이 표면으로 유출된다는 점을 고려할 때 표면유출수의 오염도를 낮추는 것이 유입오염물 저감효과에 보다 큰 효과가 있을 것으로 판단된다.문에 자료의 이상적 유지 관리가 이루어지며 복잡한 2차원 수질해석 모형을 수월하게 운영할 수 있는 시스템으로 개발하였다.제외하면, 부자측정 방법에 의한 유량산정시 가장 큰 오차원인은 홍수시 측정된 유속측선의 위치와 홍수 전후로 측정된 횡단면상의 위치가 일치하지 않는 점과, 대부분 두 측정 구간의 평균값을 대푯값으로 사용한다는 점이다. 본 연구는 다년간의 유량 측정 및 검증 경험과 자료를 토대로 현장에서 부자를 이용하여 측정된 측정성과를 정확도 높은 유량자료로 산정하는데 있어서의 문제점을 도출하고, 이로 인해 발생하는 오차를 추정하여 그 개선방안을 제시해 보고자한다. 더불어 보다 정확한 유량 산정을 위한 기준과 범주를 제시하고자 한다.리적 특성을 잘 반영하며, 도시지역의 복잡한 배수시스템 해석모형과 지표범람 모형을 통합한 모형 개발로 인해 더욱 정교한 도시지역에서의 홍수 범람 해석을 실시할 수 있을 것으로 판단된다. 본 모형의 개발로 침수상황의 시간별 진행과정을 분석함으로써 도시홍수에 대한 침수위험 지점 파악 및 주민대피지도 구축 등에 활용될 수 있을 것으로 판단된다. 있을 것으로 판단되었다.4일간의 기상변화가 자발성 기흉 발생에 영향을 미친다고 추론할 수 있었다. 향후 본 연구에서 추론된 기상변화와 기흉 발생과의 인과관계를 확인하고 좀 더 구체화하기 위한 연구가 필요할 것이다.게 이루어질 수 있을 것으로 기대된다.는 초과수익률이 상승하지만, 이후로는 감소하므로, 반전거래전략을 활용하는 경우 주식투자기간은 24개월이하의 중단기가 적합함을 발견하였다. 이상의 행태적 측면과 투자성과측면의 실증결과를 통하여 한국주식시장에 있어서 시장수익률을 평균적으로 초과할 수 있는 거래전략은 존재하므로 이러한 전략을 개발 및 활용할 수 있으며, 특히, 한국주식시장에 적합한 거래전략은 반전거래전략이고, 이 전략의 유용성은 투자자가 설정한 투자기간보다 더욱 긴 분석기간의 주식가격정보에 의하여 최대한 발휘될 수 있음을 확인하

• Journal of Conservation Science
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• v.25 no.4
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• pp.347-361
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• 2009

The Pohang Chilpori is the area with abundant petroglyphs in Korea. The form of the shield, female sex organs, and yut board on the outcrops or float rocks which are composed of the rhyolitic rock are engraved on Chilpori and Shinheungri Petroglyphs. The rhyolitic rock is composed of the phenocryst and groundmass with quartz and feldspar. The rock surface shows mostly yellowish brown color and the rock surface is very irregular by serious weathering, and illite and kaolinite, a kind of the clay minerals, are produced. Deterioration aspects are mainly of surface exfoliation, grain peel-off, damages, scribbling. Chilpori Petroglyph (1) plane has been eroded by running water, in (2) plane has been abrased is on the rock surface, in (3) plane shows surface exfoliation and the various part of the rock surface in plane (4) has become the soil. The corrasion and black phenomenon of the Shinheungri Petroglyph (1) plane was formed by running water, and surface exfoliation and scribbling in plane (2) is serious. Deterioration factors are geomorphologic states, plants, rock of weak to weathering, and artificial influence such as a scribbling and a forest fire. For conservation of the these petroglyphs, study for rock surface conservation and the arrangement of around petroglyphs and construction of water wall are necessary.

• The Journal of Engineering Geology
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• v.20 no.2
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• pp.191-202
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• 2010

In this study, the relationship between the settlements and the horizontal displacements according to embankment was analyzed at the marine sedimentary grounds for preparation of a site, and then the empirical equations of both the settlement and the horizontal displacement considering the embankment load and the thickness were proposed. To do this, the field and laboratory tests were performed at the improvement section where the pre-loading method was applied, and the field monitoring was performed using various sensors. Based on the results of the tests and monitoring, the ground deposits, soil characteristics and engineering properties were analyzed and the settlements and lateral movements were estimated by the Regression analysis. The ground deposits from the ground surface were composed of reclaimed soils, sedimentary soils and based rocks. The thickness of clay in the sedimentary soils layer was ranged from 3.9 m to 44.5 m. The embankment heights to improve the ground during pre-loading were constructed from 4.7 m to 7.8 m in each section. The settlements during embankment were ranged from 0.959 m to 2.217 m and the lateral movements were ranged from 0.048 m to 0.313 m. As the result of regression analysis, the equations of settlements and horizontal displacements according to embankments may be proposed as $s=0.02h^2+0.11h$ and ${\delta}=0.01e^{0.37h}$, respectively. The proposed empirical equations of the settlements and the horizontal displacements according to embankment on the marine sedimentary ground may be applied to the site where has a similar condition of study area.