• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.62-73
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• 2016

The variation of groundwater by wave, tide and precipitation conditions is closely related to the vegetation environment at the natural vegetation and sandy based beach, and it has a significant impact on the vegetation development and ground stabilization. In this study, the water temperature, electrical conductivity, and pressure were monitored at five observational stations normal to the Jinu-do(Island) shoreline of Nakdong river estuary from March 2012 to September 2014 (approximately 799 days) with the aim of measuring the variation in groundwater-table characteristics. The purpose of the study was to identify factors (tide, wave etc.) affecting groundwater-table variation using time series and correlation analysis, and to record spatial variations in the groundwater level and electrical conductivity as a result of storm events. The observational station in the intertidal zone was strongly affected by wave period and tide level. During the storm period, the groundwater-table and electrical conductivity were stabilized at the edge of sand dunes, vegetation, and areas of transition between freshwater and seawater.

• Journal of the Korean GEO-environmental Society
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• v.19 no.9
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• pp.21-28
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• 2018

In this study, a standard consolidation test (Oedometer) was performed on the relative density of sand in the south coast to evaluate long-term creep settlement characteristics. Experimental results show that the cumulative settlement at the final loading stage decreases as the relative density increases and the variation of the void ratio decreases. As a result of analyzing the settlement rate of long-term creep of sand, creep settlement of 4.7~11.0% occurred depending on relative density with respect to total settlement. The creep parameter, Beta, of Schmertmann et al. (1978) was estimated to be 0.17~0.40 (average 0.21), and it tended to converge to a certain value when the load step becomes more than a certain level. It was found that there is no significant difference in the creep parameter depending on the layer thickness, and it was confirmed that the creep parameter could be applied regardless of the field layer thickness.

• Journal of the Korean GEO-environmental Society
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• v.12 no.5
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• pp.13-19
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• 2011

The strength of granular mixtures can be controlled by the majority of the mixture, fine grains. However, in some cases, the small amount of gravel in the mixture may influence the strength of the mixture. In this study, the effect of some dispersed gravels on strength of sand is evaluated. Gravels are embedded in the middle of each cemented sand layer. The size and number of embedded gravels varies. After two days curing, a series of unconfined compression tests is performed on the cemented sand with dispersed gravels. In addition to that, a series of direct shear tests is also carried out on clean sand with gravels to evaluate its friction angle. For the specimens with the same ratio of gravel weight of 7% in which gravel size and number are different, an unconfined compressive strength(UCS) of a specimen with gravels decreases up to 15% compared to a specimen without gravel and then increases with increasing gravel number. For specimens embedded with the same size of gravel, UCS decreases and then increases as a number of gravel increases. As a number of gravel increases, a friction angle of clean sand with gravels decreases up to $5^{\circ}$ and then recovers up to that of a specimen without gravel.

• Journal of the Korean GEO-environmental Society
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• v.4 no.3
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• pp.51-59
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• 2003

Loading tests were carried out for model geocell to study the reinforcing effect by variation of tensile strength, cell height, soil density and embedded depth of geocell. From the result, it could be seen that the ultimate bearing capacity of the geocell system was influenced rather by the connection strength than by the tensile strength of geocell material. Bearing capacity increased with the increase of height to width ratio of geocell for the same relative density, strength and embedded depth. And the bearing capacity ratio(BCR) was higher at low relative density of sand than that of high relative density. The increase of bearing capacity was higher at geocell with high tensile strength than that of low tensile strength. And the influence was clear at higher relative density. Also the BCR was higher at shallow embedded depth of geocell. Without consideration of tensile strength of material, the application of bearing capacity formula suggested by Koerner seems not suitable for the special case with low tensile strength of geocell material.

• Journal of the Korean Geotechnical Society
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• v.36 no.9
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• pp.5-20
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• 2020

In 2017, after the Pohang earthquake, liquefaction phenomena were firstly observed after the observation of domestic earthquake by epicenter. In this study, various in-situ tests and laboratory tests were performed to determine the dynamic properties in (1) Songlim Park, (2) Heunghae-eup, Mangcheon-ri and (3) Heungan-ri, Pohang. As a site investigation, the standard penetration test (SPT), cone penetration test (CPT), multichannel analysis of surface wave (MASW), density logging, downhole test, and electrical resistivity survey were performed. In addition, cyclic triaxial test against sampled sand from site was also conducted. Based on the result, high ground water level and loose sand layer in shallow depth were observed for all sites. In addition, liquefaction resistance ratio of soil sampled from Songlim park was lower than those of Jumunjin sand, Toyoura sand, and Ottawa sand.

• Journal of Aquaculture
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• v.18 no.4
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• pp.280-286
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• 2005

Experiments were conducted to examine the differences in ammonia removal rates with the different filter media between sand and zeolite, the expanding rates between $50\%$ and $100\%$, the water temperatures between $15^{\circ}C$ and $25^{\circ}C$, and the ammonia loading rates between 2 mg/L and 5 mg/L in the seawater fluidized bed filters system (FBF). The 2.1 m high FBF (8.3 cm diameter) consisted of the clear acrylic for the upper half and a PVC pipe for the lower half, Sand and zeolite were used as the filter media in sizes of 0.5$\pm$0.1mm. Each biofilter contained 5.4 L of media. The ammonia removal rates of the biofilter were higher at the $25^{\circ}C$ water temperature than those of the biofilter at $15^{\circ}C$ water temperature, and higher at the $50\%$ expanding rate of filter media than those of the biofilter at $100\%$ expanding rate of filter media. Also, the ammonia removal rates of FBF were higher at 5 mg/L ammonia concentration than those of FBF at 2 mg/L ammonia concentration in rearing water. With these better conditions the ammonia removal rates of FBF per day are practically acceptable and ranged ken 80.6 to $210.6g/m^3$.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.207-220
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• 1999

Model tests were performed to investigate the failure modes in embankments on soft ground supported by piles with cap beams. In the model tests, Jumunjin standard sand was placed on simulated cap beams and soft ground. The cap beams are placed perpendicular to the longitudinal axis of the embankment. The colored sand and the Jmniin standard sand were placed one after the other above cap beams and soft ground to make lateral stripes with 3mm thickness in the embarkment. The colored sand was prepared by coating the Jumunjin sand with black lead powder. The photographs illustrate the two characteristic modes of failure in embarkments. One is the soil arching failure and the other is the punching shear failure. The failure mode depends on the height of embankment and the space between cap beams. That is, if the embankment is high enough compared with the space between cap beams, it will fail in arching failure. On the other hand if the embarkment is relatively low or the space between piles is too wide, it will fail in punching shear failure. The soil arching develops in embarkment as a semicylindrical arch with a thickness equal to the width of the cap beam. And the soil wedge developed above the cap beams remains intact during both arching and punching failures. The boundary of punching shear failure of the displaced soil mass can be defined on the basis of observation of the photographs.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1305-1310
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• 2005

As a way to the optimum design of the collector well lateral in riverbed filtration, experiments were performed using sand tanks which were connected to form a model lateral system. Measured were the residual hydraulic heads along the laterals, the discharge rates at each sand tank and the production rates at the collector well while the model laterals were operated with various scenarios of changing parameters including water level of the collector well, the lateral diameter and length, and the hydraulic conductivity of the sand. Results showed that riverbed filtration could be more efficient when the resistance in the lateral was weak compared with the resistance in the sand, which was indicated by the more flattened distribution of the residual hydraulic heads along the lateral. Results also showed that the discharge rate increased exponentially with the approach to the collector well, and that the exponent increased as the lateral diameter decreased and/or the hydraulic conductivity of the sand increased. It was also seen that the well production increased with the increase in the lateral length and diameter although the marginal productivity decreased. It could be concluded that the axial flow velocity in the lateral was an important factor governing the efficiency of a lateral in riverbed filtration and that the maximum entrance velocity to the collector well, over which the efficiency decreased drastically, was about 1 m/sec under the conditions of this study.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.247-256
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• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• Proceedings of the Turfgrass Society of Korea Conference
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• 2011.02a
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• pp.25-32
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• 2011

본 연구는 화력발전의 부산물로 발생하는 석탄바닥재가 골프장 사질 토양의 개량재로 사용 적합한지를 평가하기 위해 수행되었으며, 결과를 요약하면 다음과 같다. 1. 석탄바닥재의 화학성을 분석한 결과 총질소 0.34%, 가용성 인산 $52mgL^{-1}$, 치환성 칼륨 $51mgL^{-1}$ 뿐만 아니라 소량의 치환성 칼슘과 마그네슘을 함유하고 있어 식물생육에 이롭고, 유해중금속함량은 Cd, $Cr^{6+}$, Pb, Ni, As는 $1mgL^{-1}$ 이하, Cu 농도는 $1.25mgL^{-1}$ 검출되어 토양환경보전법의 토양오염우려기준 이하이므로 석탄바닥재 재활용으로 인한 토양오염 가능성은 매우 낮은 것으로 판단된다. 2. 모래 토양에 석탄바닥재를 부피비로 0~50% 비율로 혼합한 시료의 투수계수와 유효수분함량을 측정한 결과 석탄바닥재 혼합비율이 증가할수록 투수계수는 유의성 있게 감소하고 유효수분함량은 유의성 있게 증가해 석탄바닥재가 모래 토양의 낮은 수분보유력을 개선하는 효과가 있음을 확인하였다. 3. 모래 토양에 석탄바닥재를 부피비로 0~50% 비율로 혼합한 시료를 잔디식재층으로 조성한 라이시미터에 잔디종자 파종 후 약 4개월 뒤 잔디밀도가 완전히 형성된 후에 시비 후 3일 간격으로 채취한 용탈수를 분석한 결과 1일과 4일 후에 채취한 초기 용탈수에서는 석탄바닥재 혼합비율이 높을수록 $NO_3-N$, $NH_4-N$ 및 K함량이 유의성 있게 감소했으며, 대조구에 비해 석탄바닥재 혼합비율이 높은 처리구일수록 $NO_3-N$, $NH_4-N$ 및 K함량이 용탈수 채취기간 동안 지속적으로 용탈되었다. 이 결과로 석탄바닥재가 모래 토양의 낮은 양분 보유력을 개선하는데 효과적이고 석탄바닥재처리가 대조구에 비해 오랫동안 식물 생육에 필요한 양분을 공급하는 효과가 있음을 확인하였다. 4. 골프장 그린상구조와 동일한 시험포장을 만들고 모래 토양에 석탄바닥재 10%와 20% 그리고 피트, 액시스, 이소라이트를 부피비로 10% 비율로 혼합한 시료를 잔디식재층으로 조성하고 크리핑 벤트그래스(Agrostis paulstris Huds), Penn A-4 $10gm^{-2}$을 파종한 후에 처리구별로 잔디 품질을 평가하기 위해 잔디 밀도, 뿌리길이, 색상 및 시각적 품질을 조사한 결과 석탄바닥재 처리구는 기존에 사용하는 개량제인 피트, 액시스, 이소라이트 처리구와 동등한 잔디생육 촉진 효과가 있는 것으로 조사되었다. 5. 결론적으로 석탄바닥재는 골프장 토양의 물리적 특성과 화학적 특성을 개선하고 잔디생육에 필요한 양분을 공급하는데 효과적인 토양개량재라고 할 수 있다.