• Ocean Science Journal
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• 제43권4호
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• pp.223-232
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• 2008

In order to determine the temporal and spatial variations of nutrient profiles in the shallow pore water columns (upper 30 cm depth) of intertidal sandflats, we measured the salinity and nutrient concentrations in pore water and seawater at various coastal environments along the southern coast of Korea. In the intertidal zone, salinity and nutrient concentrations in pore water showed marked vertical changes with depth, owing to the active exchange between the pore water and overlying seawater, while they are temporally more stable and vertically constant in the sublittoral zone. In some cases, the advective flow of fresh groundwater caused strong vertical gradients of salinity and nutrients in the upper 10 cm depth of surface sediments, indicating the active mixing of the fresher groundwater with overlying seawater. Such upper pore water column profiles clearly signified the temporal fluctuation of lower-salinity and higher-Si seawater intrusion into pore water in an intertidal sandflat near the mouth of an estuary. We also observed a semimonthly fluctuation of pore water nutrients due to spring-neap tide associated recirculation of seawater through the upper sediments. Our study shows that the exchange of water and nutrients between shallow pore water and overlying seawater is most active in the upper 20 cm layer of intertidal sandflats, due to physical forces such as tides, wave set-up, and density-thermal gradient.

• Geomechanics and Engineering
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• 제39권1호
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• pp.73-85
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• 2024

There is growing interest in introducing artificial ground freezing (AGF) as a method to temporarily secure unstable ground during tunnel construction. In order to efficiently operate an artificial ground freezing system, basic modeling research is needed on the changes in freezing behavior according to various soil environmental conditions as well as design conditions. In this study, a thermal-hydraulic coupled analysis was performed to simulate the artificial ground freezing process of ground containing salt water. The effect of major variables, including pore water salinity, on artificial ground freezing test performance was investigated. Additionally, an artificial neural network-based prediction model was proposed to estimate the time required to achieve the desired arch thickness. The artificial neural network model demonstrated reliable accuracy (R² = 0.9942) in predicting the time it would take to reach the desired arch thickness. Among the major input variables considered, pore water salinity appeared to be the most influential input variable, and initial soil temperature showed the least importance.

• 한국수산과학회지
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• 제45권6호
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• pp.704-715
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• 2012

To examine temporal and spatial variation in salinity and nutrients in the shallow pore water of intertidal sandflats, we measured salinity and nutrient concentrations (dissolved inorganic nitrogen [DIN], phosphorus [DIP], and silicate [DSi]) in pore water of the intertidal zone along the coastline of Jeju Island at two and/or three month intervals from May 2009 to December 2010. Geochemical parameters (grain size, ignition loss [IL], chemical oxygen demand [COD], and acid volatile sulfur [AVS]) in sediment were also investigated. The surface sediments in intertidal sandflats of Jeju Island were mainly composed of sand, slightly gravelly sand and gravelly sand, with a range of mean grain size from 0.5 to 2.5 ${\O}$. Concentrations of IL and COD in sediment were higher along the eastern coast, as compared to the western coast, due to differences in biogenic sediment composition. Salinity and nutrient concentrations in pore water were markedly different across time and space during rainy seasons, whereas concentrations were temporally and spatially more stable during dry seasons. These results suggest that salinity and nutrient concentrations in pore water depend on the advective flow of fresh groundwater. We also observed an imbalance of the DIN/DIP ratio in pore water due to the influence of contaminated sources of DIN. In particular, nutrient concentrations during rainy and dry seasons were characterized by high DIN/DIP ratios (mean-127) and low DIN/DIP ratios (mean-10), respectively, relative to the Redfield ratio (16) in offshore seawater. Such an imbalance of DIN/DIP ratios in pore water can affect the coastal ecosystem and appears to cause outbreaks of benthic seaweed along the coastline of Jeju Island.

• 한국지반공학회논문집
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• 제39권11호
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• pp.53-62
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• 2023

동결토의 부동수분특성은 지반의 열-수리-역학적 거동 전반에 걸쳐 지배적인 영향을 미치며, 동결 지반의 안정성 평가를 위해서는 대상 지반재료의 부동수분특성에 대한 면밀한 검토가 필요하다. 본 연구에서는 간극수 염분농도를 고려한 동결 사질토의 부동수분곡선을 평가하기 위하여 흙의 어는점 및 부동수분을 측정하는 실내 실험을 수행하였으며, 계측된 실험데이터를 기반으로 부동수분포화도 곡선을 간편하게 추정할 수 있는 경험적 모델을 새롭게 제시하였다. 또한, 제안된 경험적 모델을 입력자료로 적용한 해석모델의 시뮬레이션 결과를 실험데이터와 비교함으로써 사용된 부동수분곡선의 적정성을 검증하였다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
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• pp.307-312
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• 2007

Seawater intrusion in estuarine regions is an important issue in protecting groundwater against salinity increase as well as in protecting construction materials against corrosion. For example, drain water ejected during accelerated consolidation for the improvement of soft ground can cause damages to farm land because the drain water from seawater intrusion zones contains salinity. In this study, we have employed correlation analysis between resistivity value and salinity of in situ pore water. The correlation analysis indicates that resistivity and salinity are in exponential relationship with good correlation. Therefore we suggest that rapid estimation of spatial distribution of NaCl is possible using resistivity data.

• Membrane and Water Treatment
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• 제9권1호
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• pp.53-62
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• 2018

In this study, vacuum membrane distillation (VMD) was used to treat high-salinity wastewater (concentration about 17%) discharged by chlor-alkali plant after resin regeneration. The feasibility of VMD for the treatment of real saline wastewater by using Polyvinylidene fluoride (PVDF) microporous plate membrane with a pore diameter of $0.2{\mu}m$ was investigated. The effects of critical operating parameters such as feed temperature, velocity, vacuum degree and concentration on the permeate water flux were analyzed. Numerical simulation was used to predict the flux and the obtained results were in good agreement with the experimental data. The results showed that an increase in the operating conditions could greatly promote the permeate water flux which in turn decreased with an increase in the concentration. When the concentration varied from 17 to 25%, the permeate water flux dropped marginally with time indicating that the concentration was not sensitive to the decrease in permeate water flux. The permeate water flux decreased sharply until zero due to the membrane fouling resistance as the concentration varied from 25 to 26%. However, the conductivity of the produced water was well maintained and the average value was measured to be $4.98{\mu}s/cm$. Furthermore, a salt rejection of more than 99.99% was achieved. Overall, the outcome of this investigation clearly indicates that VMD has the potential for treating high-salinity wastewater.

• 한국터널지하공간학회 논문집
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• 제18권5호
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• pp.401-412
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• 2016

고수압 조건의 해저터널 공사에 기존의 그라우팅 공법은 제한을 받게 되어 굴착작업이 어려울 수 있으나, 인공동결공법을 적용할 경우 신속한 차수 및 지반보강 효과를 얻을 수 있다. 인공동결공법을 적용할 경우, 동결 조건에 따라 동결토의 거동이 크게 변화하므로 기존의 연구 사례를 바탕으로 해저지반 등 특수한 조건에서 동결토의 역학적 거동을 예측하는 것에는 한계가 있다. 또한, 인공동결공법의 설계를 위해서는 동결체 형성에 필요한 소요시간 및 동결범위를 산정해야 하며, 해저지반의 경우 간극수 내 염분의 영향을 반영해야 한다. 본 논문에서는 동결토의 열적 특성을 파악하기 위해 인조규사 시료에 대한 실내 열전도도 측정시험과 동결챔버시험을 수행하였다. 동결토와 비동결 포화토 간극수의 염도를 조절하여 동결 과정과 염분에 따른 유효 열전도도를 비정상 열선법을 적용하여 측정하였다. 인조규사 간극수의 염도에 의한 동결특성 변화를 파악하기 위해 동결챔버를 설계 및 제작하였고 이를 통하여 동결 조건을 변화시키며 동결챔버시험을 수행하였다. 동결 조건에 따른 시료내 온도 변화를 분석하고 이를 통해 동결 조건이 사질토의 열전달 특성에 미치는 영향을 평가하였다. 비동결 포화토의 경우는 간극수가 담수(염도 0%)인 조건과 염수(염도 3.5%)인 조건 모두 유효 열전도도가 유사하게 평가되었으나, 동결토의 경우는 간극수가 염수인 조건이 보다 큰 유효 열전도도를 보였다. 이는 동결챔버시험에서 간극수가 염수인 조건이 담수인 조건보다 동결속도가 더 빠른 결과와 일치한다.

• Geomechanics and Engineering
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• 제33권1호
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• pp.113-120
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• 2023

Coastal and offshore structures such as ports and offshore wind farms will often need to be built on fine-grained sediments. Geotechnical properties associated with sediment compressibility are key parameters for marine construction designs especially on soft grounds, which involve clay-mineral dominated fines that can consolidate and settle significantly in response to engineered and environmental loads. We conduct liquid limit tests and 1D consolidation tests with fine-grained soils (silica silt, mica, kaolin and bentonite) and biogenic soils (diatom). The pore fluids for the liquid limit tests include deionized water and a series of brines with NaCl salt concentrations of 0.001 m, 0.01 m, 0.1 m, 0.6 m and 2.0 m, and the pore fluids for the consolidation tests deionized water, 0.01 m, 0.6 m, 2 m. The salt concentrations help the liquid limits of kaolin and bentonite decrease, but those of diatom slightly increase. The silica silt and mica show minimal changes in liquid limit due to salt concentrations. Accordingly, compression indices of soils follow the trend of the liquid limit as the liquid limit determined the initial void ratio of the consolidation test. Diatoms are more likely to be broken than clastic sediments during to loading, and diatom-rich sediment is therefore generally more compressible than clastic-rich sediment.

• 한국수산과학회지
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• 제45권6호
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• pp.694-703
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• 2012

To understand the characteristics of sedimentary and benthic environments in habitats of naturally-occurring intertidal benthic macroalgae, various geochemical parameters of sediment (grain size, ignition loss [IL], chemical oxygen demand [COD], and acid volatile sulfur [AVS]) and pore water (temperature, salinity, pH, and nutrients) were measured in the southern intertidal zone of Hampyeong Bay at two month intervals from April to October 2009. Ecological characteristics including the distribution and biomass of benthic macroalgae were also investigated. Benthic macroalgae were distributed below 4 to 5 m depth from mean sea level near the lower portion of the intertidal zone where air exposure time is relatively short. The distribution area and biomass of benthic macroalgae gradually decreased during the study period. The surface sediments in the benthic algal region were mainly composed of finer sediments, such as slightly gravelly mud and mud. The temperature, salinity, pH, and nutrient concentrations (except dissolved inorganic nitrogen) in pore water did not differ in regions with and without benthic macroalgae, whereas the mean grain size and the concentrations of IL, COD, and AVS in sediments were much higher in regions harboring benthic macroalgae. The correlation between mean grain size and IL in sediments displayed two distinct gradients and the slope was much steeper in regions harboring benthic macroalgae, indicating that the content of organic matter in benthic algal region is not solely dependent on mean grain size. Our results indicate that the benthic macroalgae in the southern intertidal zone of Hampyeong Bay play an important role in the accumulation of organic matter in sediment.

• 한국지하수토양환경학회지:지하수토양환경
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• 제21권3호
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• pp.35-48
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• 2016

A micromodel was applied to estimate the effects of geological conditions and injection methods on displacement of resident porewater by injecting scCO₂ in the pore scale. Binary images from image analysis were used to distinguish scCO₂-filled-pores from other pore structure. CO₂ flooding followed by porewater displacement, fingering migration, preferential flow and bypassing were observed during scCO₂ injection experiments. Effects of pressure, temperature, salinity, flow rate, and injection methods on storage efficiency in micromodels were represented and examined in terms of areal displacement efficiency. The measurements revealed that the areal displacement efficiency at equilibrium decreases as the salinity increases, whereas it increases as the pressure and temperature increases. It may result from that the overburden pressure and porewater salinity can affect the CO₂ solubility in water and the hydrophilicity of silica surfaces, while the neighboring temperature has a significant effect on viscosity of scCO₂. Increased flow rate could create more preferential flow paths and decrease the areal displacement efficiency. Compared to the continuous injection of scCO₂, the pulse-type injection reduced the probability for occurrence of fingering, subsequently preferential flow paths, and recorded higher areal displacement efficiency. More detailed explanation may need further studies based on closer experimental observations.