• Journal of the Korean Geotechnical Society
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• v.26 no.12
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• pp.19-30
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• 2010

Bentonite-based grout has been widely used to seal a borehole constructed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. Three types of bentonites were compared one another in terms of viscosity and thermal conductivity in this paper. The viscosity and thermal conductivity of the grouts with bentonite contents of 5%, 10%, 15%, 20% and 25% by weight were examined to take into account a variable water content of bentonite grout depending on field conditions. To evaluate the effect of salinity (i.e., concentration of NaCl : 0.1M, 0.25M, and 0.5M) on swelling potential of the bentonite-based grouts, a series of volume reduction tests were performed. In addition, if the viscosity of bentonite-water mixture is relatively low, particle segregation can occur. To examine the segregation phenomenon, the degree of segregation has been evaluated for the bentonite grouts especially in case of relatively low viscosity. From the experimental results, it is found that (1) the viscosity of the bentonite mixture increased with time and/or with increasing the mixing ratio. However, the thermal conductivity of the bentonite mixture did not increase with time but increased with increasing the mixing ratio; (2) If bentonite grout has a relatively high swelling index, the volume reduction ratio in the saline condition will be low; (3) The additive, such as a silica sand, can settle down on the bottom of the borehole if the bentonite has a very low viscosity. Consequently, the thermal conductivity of the upper portion of the ground heat exchanger will be much smaller than that of the lower portion.

• Korean Journal of Environmental Agriculture
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• v.22 no.4
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• pp.278-283
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• 2003

This study was carried out to examine the nitrogen removal rate of a subsurface-flow treatment wetland system which was constructed on floodplain of the Kwangju River from May to June 2001. Its dimensions were 29m in length, 9m in width and 0.65m in depth. A bottom layer of 45cm in depth was filled with crushed granite with about $15{\sim}30\;mm$ in diameter and a middle layer of 10cm in depth had pea pebbles with about 10 mm in diameter. An upper layer of 5 cm in depth contained course sand. Reeds (Phragmites australis) were transplanted on the surface of the system. They were dug out of natural wetlands and stems were cut at about 40 cm height from their bottom ends. Water of the Kwangju River flowed into it via a pipe by gravity flow and its effluent was funneled back into the river. The height of reed stems was 44.2 cm in July 2001 and 75.3cm in September 2001. The number of stems was increased from $80\;stems/m^2$ in July 2001 to $136\;stems/m^2$ in September 2001. Volume and water quality of inflow and outflow were analyzed from July 2001 through December 2001. Inflow and outflow averaged 40.0 and $39.2\;m^3/day$, respectively. Hydraulic detention time was about 1.5 days. Average nitrogen uptake by reeds was $69.31\;N\;mg/m^2/day$. Removal rate of $NO_3-N$, $NH_3-N$, T-N averaged 195.58, 53.65, and $628.44\;mg/m^2/day$, respectively. Changes of $NO_3-N$ and $NH_3-N$ abatement rates were closely related to those of wetland temperatures. The lower removal rate of nitrogen species compared with that of subsurface-flow wetlands operating in North America could be attributed to the initial stage of the system and inclusion of two cold months into the six-month monitoring period. Increase of standing density of reeds within a few years will develop both root zones suitable for the nitrification of ammonia and surface layer substrates beneficial to the denitrification of nitrates into nitrogen gases, which may lead to increment in the nitrogen retention rate.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.4
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• pp.23-29
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• 2017

The packaged optical fiber Bragg grating sensors which were networked by multiplexing the Bragg grating sensors with WDM technology were investigated in application for the structural health monitoring of the marine trestle structure transporting the ship. The optical fiber Bragg grating sensor was packaged in a cylindrical shape made of aluminum tubes. Furthermore, after the packaged optical fiber sensor was inserted in polymeric tube, the epoxy was filled inside the tube so that the sensor has resistance and durability against sea water. The packaged optical fiber sensor component was investigated under 0.2 MPa of hydraulic pressure and was found to be robust. The number and location of Bragg gratings attached at the trestle were determined where the trestle was subject to high displacement obtained by the finite element simulation. Strain of the part in the trestle being subjected to the maximum load was analyzed to be ${\sim}1000{\mu}{\varepsilon}$ and thus shift in Bragg wavelength of the sensor caused by the maximum load of the trestle was found to be ~1,200 pm. According to results of the finite element analysis, the Bragg wavelength spacings of the sensors were determined to have 3~5 nm without overlapping of grating wavelengths between sensors when the trestle was under loads and thus 50 of the grating sensors with each module consisting of 5 sensors could be networked within 150 nm optical window at 1550 nm wavelength of the Bragg wavelength interrogator. Shifts in Bragg wavelength of the 5 packaged optical fiber sensors attached at the mock trestle unit were well interrogated by the grating interrogator which used the optical fiber loop mirror, and the maximum strain rate was measured to be about $235.650{\mu}{\varepsilon}$. The modelling result of the sensor packaging and networking was in good agreements with experimental result each other.

• Journal of the Korean Association of Geographic Information Studies
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• v.22 no.4
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• pp.39-58
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• 2019

This study performed the dam watershed storm runoff modeling using GPM(Global Precipitation Measurement) satellite rain and KIMSTORM2(KIneMatic wave STOrm Runoff Model 2) distributed model. For YongdamDam watershed(930㎢), three heavy rain events of 25th August 2014, 11th September 2017, and 26th June 2018 were selected and tested for 4 cases of spatial rainfalls such as (a) Kriging interpolated data using ground observed data at 7 stations, (b) original GPM data, (c) GPM corrected by CM(Conditional Merging), and GPM corrected by GDA(Geographical Differential Analysis). For the 4 kinds of data(Kriging, GPM, CM-GPM, and GDA-GPM), the KIMSTORM2 was calibrated respectively using the observed flood discharges at 3 water level gauge stations(Cheoncheon, Donghyang, and Yongdam) with parameters of initial soil moisture contents, stream Manning's roughness coefficient, and effective hydraulic conductivity. The total average Nash-Sutcliffe efficiency(NSE) for the 3 events and 3 stations was 0.94, 0.90, 0.94, and 0.94, determination coefficient(R²) was 0.96, 0.92, 0.97 and 0.96, the volume conservation index(VCI) was 1.03, 1.01, 1.03 and 1.02 for Kriging, GPM, CM-GPM, and GDA-GPM applications respectively. The CM-GPM and GDA-GPM showed better results than the original GPM application for peak runoff and runoff volume simulations, and they improved NSE, R², and VCI results.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.4
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• pp.113-120
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• 2006

Wastewater generated through the food waste recycling process have known high concentration, BOD 20,000~150,000 mg/L, which has to treat to the proper level because of a ban on reclamation. But it is impossible to treat less than 10 days by existing water treatment plant. Ecodays Ltd. is to treat this wastewater during 2~4 days by ER-1, which can simultaneously induce the modified PFR(Plug Flow Reactor) of the oxygen transfer rate, MLVSS concentration, and influent concentration to top from bottom of reactor. We tested the pilot test about low concentration food wastewater(BOD 16,500 mg/L) and high concentration food wastewater(64,431 mg/L) at the food waste recycling plant of H-Gun(20t/d). Hydraulic retention time(HRT) of ER-1 for low concentration food wastewater is 2.5day. In low concentration conditions, ER-1 treatment efficiency is to appear BOD 99%, COD 98%, TN 97%, and TP 96%. While ER-1 process for high concentration food wastewater treatment is composed 2 stages, which are to be HRT 2.5day for law wastewater and HRT 1.5 day for secondary treatment. In high concentration conditions, ER-1 treatment efficiency is to appear BOD 97%, COD 84%, TN 66%, and TP 95%. It is treated without temperature control about high temperature($50^{\circ}C$) to appear low treatment efficiency in high concentration conditions.

• Journal of Wetlands Research
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• v.19 no.3
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• pp.318-326
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• 2017

Riverine wetlands were reduced and damaged by dredging of rivers and constructing parks in wetlands by Four Rivers Project from 2008 to 2013. Therefore, replacement wetlands were constructed for the compensation of wetland loss by the government. However, It is not enough to manage replacement wetlands. In order to manage the wetlands efficiently, it is necessaty to assess the functions of the wetlands and to manage them according to their functions. Here we performed functional assessments for a replacement wetland called Gangcheon wetland using the modified HGM approach. Hydrological, biogeochemical, animal habitat, and plant habitat functions for the wetland were assessed. To assess the functions, we collected informations for modified HGM approach from the monitored hydrologic data, field survey, published reports and documents for before and after the project, and hydraulic & hydrologic modeling. As the results of the assessment, the hydrological function for the replacement wetland showed 65.5% of the reference wetland, biogeochemical function showed 66.6%, plant habitat function showed 75%, and animal habitat function showed 108.3%. Overall, Gangcheon wetland function after the project was reduced to 78.9% of the function before the project. The decrease in hydrological function is due to the decrease of subsurface storage of water. And the decrease in biogeochemical & pland habitat functions is due to the removal of sandbank around the Gangcheon wetland. To compensate for the reduced function, it is necessary to expand the wetland area and to plant the various vegetation. The modified HGM used in this study can take into account the degree of improvement for replacement wetlands, so it can be used to efficiently manage the replacement wetlands. Also when the wetland is newly constructed, it will be very useful to assess the change of function of the wetland over time.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.29-46
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• 2004

It is important to identify geometries of fracture that act as a conduit of fluid flow for characterization of ground water flow in fractured rock. Fracture geometries control hydraulic conductivity and stream lines in a rock mass. However, we have difficulties to acquire whole geometric data of fractures in a field scale because of discontinuous distribution of outcrops and impossibility of continuous collecting of subsurface data. Therefore, it is needed to develop a method to describe whole feature of a target fracture geometry. This study suggests a new approach to develop a method to characterize on the whole feature of a target fracture geometry based on the Fourier transform. After sampling of specimens along a target fracture from borehole cores, effective frequencies among roughness components were selected by the Fourier transform on each specimen. Then, the selected effective frequencies were averaged on each frequency. Because the averaged spectrum includes all the frequency profiles of each specimen, it shows the representative components of the fracture roughness of the target fracture. The inverse Fourier transform is conducted to reconstruct an averaged whole roughness feature after low pass filtering. The reconstructed roughness feature also shows the representative roughness of the target subsurface fracture including the geometrical characteristics of each specimen. It also means that overall roughness feature by scaling up of a fracture. In order to identify the characteristics of permeability coefficients along the target fracture, fracture models were constructed based on the reconstructed roughness feature. The computation of permeability coefficient was performed by the homogenization analysis that can calculate accurate permeability coefficients with full consideration of fracture geometry. The results show a range between $10^{-4}{\;}and{\;}10^{-3}{\;}cm/sec$, indicating reasonable values of permeability coefficient along a large fracture. This approach will be effectively applied to the analysis of permeability characteristics along a large fracture as well as identification of the whole feature of a fracture in a field scale.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.47-56
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• 2020

In this study, three levels of W/B(Water to Binder) ratio (0.37, 0.42, 0.47) and substitution ratio of GGBFS (Ground Granulated Blast Furnace Slag) rate (0 %, 30 %, 50 %) were considered to perform RCPT (Rapid Chloride Diffusion Test) at the 1,095 aged day. Accelerated chloride diffusion coefficient and passed charge of each concrete mixture were assessed according to Tang's method and ASTM C 1202, and improving behaviors of durability performance with increasing aged days are analyzed based on the test results of previous aged days from the preceding study. As the age of concrete increases, the passed charge and diffusion coefficient have been significantly reduced, and especially the concrete specimens containing GGBFS showed a significantly more reduction than OPC(Ordinary Portland Cement) concrete specimen by latent hydraulic activity. In the case of OPC concrete's results of passed charge, at the 1,095 days, two of them were still in the "Moderate" class. So, if only OPC is used as the binder of concrete, the resistance performance for chloride attack is weak. In this study, the time-parameters (m) were derived based on the results of the accelerated chloride diffusion coefficient, and the deterministic and probabilistic analysis for service life were performed by assuming the design variable as a probability function. For probabilistic service life analysis, durability failure probabilities were calculated using Monte Carlo Simulation (MCS) to evaluate service life. The service life of probabilistic method were lower than that of deterministic method, since the target value of PDF (Probability of Durability Failure) was set very low at 10 %. If the target value of PDF suitable for the purpose of using structure can be set and proper variability can be considered for each design variable, it is believed that more economical durability design can be made.

• Tunnel and Underground Space
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• v.32 no.5
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• pp.285-297
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• 2022

We report results of Extended Leak-Off Test (XLOT) conducted in a large diameter borehole, which is drilled for installation of deep borehole geophysical monitoring system to monitor micro-earthquakes and fault behavior of major fault zones in the southeastern Korean Peninsula. The borehole was planned to secure a final diameter of 200 mm (or more) at a depth of ~1 km, with 12" diameter wellbore to intermediate depths, and 7-7/8" (~200 mm) to the bottom hole depth. We drilled first the 12" borehole to approximately 504 m deep and installed American Petroleum Institute standard 8-5/8" casing, then annulus between the casing and bedrock was fully cemented. XLOT was carried out for several purposes such as confirming casing and cementing integrity, measuring rock stress states. To that end, we drilled additional 4 m long open hole interval to directly inject water and pressurize into the rock mass using the upper API casings. During the XLOT, flow rates and interval pressures were recorded in real time. Based on the logs we tried to analyze hydraulic conductivity of the test interval.

• Economic and Environmental Geology
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• v.56 no.4
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• pp.435-445
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• 2023

A delta is a depositional landform that is formed when sediment transported by a river is deposited in a relatively low-energy environment, such as a lake, sea, or a main channel. Among these, a delta formed at the confluence of rivers has a great importance in river management and research because it has a significant impact on the hydraulic and sedimentological characteristics of the river. Recently, the equilibrium state of the confluence area has been disrupted by large-scale dredging and construction of levees in the Nakdong River. However, due to the natural recovery of the river, the confluence area is returning to its pre-dredging natural state through ongoing sedimentation. The time-series data show that the confluence delta has been steadily growing since the dredging, but once it reaches a certain size, it repeats growth and retreat, and the overall size does not change significantly. In this study, we developed a model to explain the sedimentation-erosion processes in the confluence area based on the assumption that the confluence delta reaches a dynamic equilibrium. The model is based on two fundamental principles: sedimentation due to supply from the tributary and erosion due to the main channel. The erosion coefficient that represents the Nakdong River confluence areas, was obtained using data from the tributaries of the Nakdong River. Sensitivity analyses were conducted using the developed model to understand how the confluence delta responds to changes in the sediment and water discharges of the tributary and the main channel, respectively. We then used annual average discharge of the Nakdong River's tributaries to predict the dynamic equilibrium positions of the confluence deltas. Finally, we conducted a simulation experiment on the development of the Gamcheon-Nakdong River delta using recorded daily discharge. The results showed that even though it is a simple model, it accurately predicted the dynamic equilibrium positions of the confluence deltas in the Nakdong River, including the areas where the delta had not formed, and those where the delta had already formed and predicted the trend of the response of the Gamcheon-Nakdong River delta. However, the actual retreat in the Gamcheon-Nakdong River delta was not captured fully due to errors and limitations in the simplification process. The insights through this study provide basic information on the sediment supply of the Nakdong River through the confluence areas, which can be implemented as a basic model for river maintenance and management.