Tae-Hyuk Kwon - Academia.edu (original) (raw)

Papers by Tae-Hyuk Kwon

Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)

This is an Open-Access article distributed under the terms of the Creative Commons Attribution No... more This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited The acoustic emission (AE) is proposed as a feasible method for the real-time monitoring of the structural damage evolution in concrete materials that are typically used in the storage of nuclear wastes. However, the characteristics of AE signals emitted from concrete structures subjected to various environmental conditions are poorly identified. Therefore, this study examines the AE characteristics of the concrete structures during uniaxial compression, where the storage temperature and immersion conditions of the concrete specimens varied from 15℃ to 75℃ and from completely dry to water-immersion, respectively. Compared with the dry specimens, the water-immersed specimens exhibited significantly reduced uniaxial compressive strengths by approximately 26%, total AE energy by approximately 90%, and max RA value by approximately 70%. As the treatment temperature increased, the strength and AE parameters, such as AE count, AE energy, and RA value, of the dry specimens increased; however, the temperature effect was only minimal for the immersed specimens. This study suggests that the AE technique can capture the mechanical damage evolution of concrete materials, but their AE characteristics can vary with respect to the storage conditions.

Debris flows are one of the most serious hazards in the mountainous areas. To assess and mitigate... more Debris flows are one of the most serious hazards in the mountainous areas. To assess and mitigate the debris-flow hazard, debrisflow intensities and deposition on fans must be estimated. Rheological properties including yield stress and viscosity are major parameters to describe and predict behaviors of debris flow. In the present study, the effect of rheological properties on debris-flow intensities and deposition on fans of natural clay was investigated using large scale flume experiments. The experimental device employed in the tests consists of a tilting flume with an inclination 17°, on which a steel tank with a removable gate was installed. A final horizontal plane works as the deposition area. Natural soil samples of different water contents were tested. Rheological properties of soil mixtures were obtained from vane-rheometer tests. Non-linear regression analysis was used to assess the effect of yield stress and viscosity on debris-flow velocity, runout distance, deposited a...

Studies for analysis and monitoring to prevent drought have been conducted. However, most of the ... more Studies for analysis and monitoring to prevent drought have been conducted. However, most of the studies carried out mainly from the meteorological and hydrological perspectives, and there is a lack of research on the observation of soil changes caused by drought. Therefore, in order to minimize or prevent the crop damage caused by desiccation cracks caused by persistent drought, and damage to farmers and to structures, electromagnetic waves in the terahertz region was used to investigate the moisture condition of the soil materials using femto second terahertz pulse-laser. Transmittance, reflectance, extinction, and extinction coefficient of the soil samples with water content for terahertz frequencies were calculated and THz images of desiccation cracks of the clay were measured.

With growing interests in utilizing soft biological materials for soil improvement, it is crucial... more With growing interests in utilizing soft biological materials for soil improvement, it is crucial to understand the mechanical characteristics biopolymers to predict the behavior of the biopolymer-treated soils. This study presents rheological parameters of insoluble and porous polysaccharidic biopolymer, which has a potential to be used for soil enrichment. Due to the internal porosity and high heterogeneity of dextran, the traditional rheometer would be inadequate to measure representative properties. Instead, particle-tracking microrheology technique was employed to obtain reliable rheological properties of dextran in liquid where Brownian motions of small fluorescent beads trapped in porous dextran structure were recorded at 100 Hz. The frequencydependent complex shear moduli were found; the storage modulus ranged ~0.01–0.1 Pa and the loss modulus was in the range of ~0.001–0.1 Pa in the frequency of ~1–100 Hz.

Journal of the Korean Geotechnical Society, 2020

Permeation grouting effectively enhances soil strength and decreases permeability of soil; howeve... more Permeation grouting effectively enhances soil strength and decreases permeability of soil; however, the flow of grout is heavily affected by anisotropy of hydraulic conductivity in layers. Therefore, this study investigates the effect of permeability anisotropy on the effective radius of horizontal permeation grout using computational fluid dynamics (CFD). We modeled the horizontal permeation grout flow as a two-phase viscous fluid flow in porous media, and the model incorporated the chemical diffusion and the viscosity variation due to hardening. The numerical simulation reveals that the permeability anisotropy shapes the grout bulb to be elliptic and the dissolution-driven diffusion causes a gradual change in grout pore saturation at the edge of the grout bulb. For the grout pore saturations of 10%, 50% and 90%, the horizontal and vertical radii of grout bulb are estimated when the horizontal-to-vertical permeability ratio varies from 0.01 to 100, and the predictive model equation...

Applied Sciences, 2020

Acoustic emission (AE) has garnered significant interest as a promising way to detect the early-s... more Acoustic emission (AE) has garnered significant interest as a promising way to detect the early-stage development of internal cracks and damage in underground and geotechnical structures, associated with natural disasters. Meanwhile, AE source localization techniques that can identify the damage location in a piled-raft foundation (PRF) are premature because of its complex geometry, although the PRF is a widely used deep foundation type for high-rise buildings. In this study, we propose an integrated approach to localize AE sources in the PRF by using the modified Akaike information criterion (AIC) method and examine its accuracy to mark with pile zones. We performed a series of experiments on a scaled PRF model at a ratio of 1:50, composed of one raft and 25 piles. The results demonstrate that the combined approach with the modified AIC method and the Simplex method can localize the AE source zones with good accuracy, greater than 95% on average. The suggested two-stage AIC picker ...

Landslides, 2020

Debris flows are one of the perilous landslide-related hazards due to their fast flow velocity, l... more Debris flows are one of the perilous landslide-related hazards due to their fast flow velocity, large impact force, and long runout, in association with poor predictability. Debris-flow barriers that can minimize the energy of debris flows have been widely constructed to mitigate potential damages. However, the interactions between debris flows and barriers remain poorly understood, which hampers the optimal barrier installation against debris flows. Therefore, this study examined the effect of barrier locations, in particular source-to-barrier distance, on velocity and volume of debris flows via the numerical approach based on smoothed particle hydrodynamics (SPH). A debris-flow event was simulated on a 3D terrain, in which a closed-type barrier was numerically created at predetermined locations along a debris-flow channel, varying the source-to-barrier distance from the initiation point. In all cases, the closed-type barrier significantly reduced the velocity and volume of the deb...

Géotechnique Letters, 2020

Exocultured biopolymers are ecofriendly soil-stabilisation agents with superior particle bonding,... more Exocultured biopolymers are ecofriendly soil-stabilisation agents with superior particle bonding, hydrogel-formation characteristics and zero endoculture duration. However, the use of exocultured biopolymers for enhancing soil resistance against surface erosion by water flow is yet to be investigated. Using erosion function apparatus (EFA) in combination with an ultrasonic P-wave reflection monitoring device, the effect of exocultured biopolymers on the erosion parameters of critical shear stress and the erodibility coefficient was examined in this study in soils with different particle distributions. In this way, biopolymer soil treatment showed a ten-fold increase in critical shear stress along with a 90% reduction in erodibility coefficient; results which could be attributed to enhanced particle-to-particle contact and increased pore-fluid viscosity and pore clogging. The results of this study demonstrate the feasibility of using exocultured biopolymers in mitigating surface eros...

Journal of the Korean Society of Hazard Mitigation, 2019

Accurate estimation of the permeability of soils plays a major role in many geotechnical engineer... more Accurate estimation of the permeability of soils plays a major role in many geotechnical engineering practices. Advances in X-ray computed microtomography (X-ray microCT) have facilitated the direct use of high-resolution images for numerical simulation. In this study, a sand column was prepared and its pore-scale images were acquired using X-ray microCT scanning. The resulting images were converted into a finite volume mesh format using Python-based code for computational fluid dynamics. A Navier-Stokes equation was used to solve the flow in the constructed pore structure, and the permeability was computed based on Darcy's law. The computed permeability showed fairly good agreement with the measured value with 26% error. Further improvement in mesh generation technique is necessary because of the insufficient resolution near walls and grain contacts. However, this study suggests the feasibility of using X-ray CT imaging for numerical computation of permeability and the relevant transport properties of porous media.

Water Resources Research, 2019

Abiotic carbonate precipitation has garnered significant interest as a mechanism for mineral trap... more Abiotic carbonate precipitation has garnered significant interest as a mechanism for mineral trapping of carbon dioxide (CO 2) in geologic carbon storage, as a natural diagenetic process frequently occurring in marine environments, and as an engineering approach for soil improvement. This study explored pore-scale precipitation of calcium carbonate (CaCO 3) and its effect on the permeability of porous media, using X-ray computed microtomography (CMT). In a column experiment, CaCO 3 was precipitated in a sand pack from a supersaturated CaCO 3 solution, while porosity, pore volume fraction of carbonate, and permeability were being monitored and X-ray CMT images were being acquired. Permeability reduction by~99.94% was observed when precipitated carbonate occupied~46-47% of pore volume. The X-ray CMT images showed that carbonate crystals were initially nucleated onto sand grain surfaces, which facilitated subsequent precipitation, indicating a predominantly grain-coating behavior. The scanning electron microscopy revealed the carbonate crystals of~1-20 μm in size and the presence of internal pores in the carbonate layers at the submicrometer scale. Variations in carbonate layer thickness and geometric tortuosity, and preferential carbonate precipitation behavior with local clogging were examined through morphological analysis and phase segmentation. Particularly, the pore-scale precipitation pattern and hence the pore geometry were found to evolve with continued precipitation from a grain-coating behavior, through a pore-filling behavior, and finally into a dramatic pore-throat-clogging behavior. Our results provide unique experiment data for predictive modeling of long-term CO 2 transport and provide new insights into the changes in physical and transport properties during CO 2 mineral trapping.

Journal of the Korean Society of Hazard Mitigation, 2018

Fluid flow inside the levee can causes fines migration induced by internal erosion phenomenon. Fi... more Fluid flow inside the levee can causes fines migration induced by internal erosion phenomenon. Fines migration can change stiffness or pore water pressure of levee, and without proper treatment the levee may collapse in a sudden. But, at present, research on internal erosion caused by fluid flow in domestic and overseas is insufficient. Therefore, in this study, we analyze the effect of fine particle, fluids, and the combined effect of both, through experiments, to the fines migration behavior inside the levee. Through experiments, it was confirmed that the effect of fine particle is the factor that dominate the movement of fine particle, and the interface between water and air increases the movement of fine particle, but the number of interfaces did not. By considering factors influencing the fines migration, we can evaluate the change of the safety of the levee.

Geotechnical Testing Journal, 2016

Erosion of soils in river, lake, and seabeds is an important component for scour estimation and d... more Erosion of soils in river, lake, and seabeds is an important component for scour estimation and design of underwater structures. This is because the scour can cause severe structural damage to underwater foundations or embankments. The erosion function apparatus (EFA) method is widely used to estimate the erosion rate of soils in the laboratory, where a soil protrusion of 1 mm thick is exposed to water flow and the time taken to erode this protrusion is measured. However, determining this erosion time is a difficult task because it is only visually inspected, and this can cause considerable measurement errors. Therefore, this study explored the feasibility of using an ultrasonic P-wave reflection monitoring method to more quantitatively assess the erosion rate that otherwise has been measured by visual inspection. The erosion rates were monitored using ultrasonic transducers mounted above a soil surface during the EFA testing on the prepared soil samples containing different clay fractions. Via the P-wave monitoring results, several important semi-quantitative observations were made: an increase in erosion resistance with an increase in the clay fraction, a discontinuous erosion behavior of fine-grained soils with sudden removal of soil lumps by water flows, a continuous erosive action of coarse-grained soils, and inherent heterogeneous erosion even at a specimen scale (i.e., the scale of milli-to-centimeter). While both the P-wave monitoring method and the visual inspection showed similar estimation on the erosion rate, the former was found to provide overall better quantitative assessment, particularly in conditions of very slow or rapid erosion and in the conditions with high turbidity water, unevenly eroded sample surfaces, or limited control on the soil protruding thickness.

Japanese Geotechnical Society Special Publication, 2016

Soil erosion resistance is an important engineering parameter to assess scouring processes at bri... more Soil erosion resistance is an important engineering parameter to assess scouring processes at bridge piers. Among other many methods for estimating erosion rate of soils, such as the hole erosion test and the submerged jet erosion test, the SRICOS-EFA (scour rate in cohesive soil-erosion function apparatus) method is often used to estimate soil erodibility in laboratory. This method measures the time taken to erode and remove a 1-mm-thick soil layer when the surface of a soil specimen is exposed to water flow with a constant flow rate. However, determining this duration time taken for the 1 mm erosion depth is a challenging task, causing measurement errors. This study explores the feasibility of implementation of a P-wave monitoring technique to more accurately determine the erosion time. P-wave monitoring results during the SRICOS-EFA erosion test were presented and the erosion rates obtained by a conventional method and by our new proposed technique were compared. By monitoring the arrival time of reflected P-waves, the changes in the depth of the soil surface during erosion process were precisely estimated. It revealed that this P-wave monitoring method provided more accurate measurement of the erosion rate.

Environmental science & technology, Jan 13, 2018

Natural gas hydrates are found widely in oceanic clay-rich sediments, where clay-water interactio... more Natural gas hydrates are found widely in oceanic clay-rich sediments, where clay-water interactions have a profound effect on the formation behavior of gas hydrates. However, it remains unclear why and how natural gas hydrates are formed in clay-rich sediments in spite of factors that limit gas hydrate formation, such as small pore size and high salinity. Herein, we show that polarized water molecules on clay surfaces clearly promote gas hydrate nucleation kinetics. When water molecules were polarized with an electric field of 10V/m, gas hydrate nucleation occurred significantly faster with an induction time reduced by 5.8 times. Further, the presence of strongly polarized water layers at the water-gas interface hindered gas uptake and thus hydrate formation, when the electric field was applied prior to gas dissolution. Our findings expand our understanding of the formation habits of naturally occurring gas hydrates in clay-rich sedimentary deposits and provide insights into gas pro...

Journal of synchrotron radiation, 2017

Continuous improvements at X-ray imaging beamlines at synchrotron light sources have made dynamic... more Continuous improvements at X-ray imaging beamlines at synchrotron light sources have made dynamic synchrotron X-ray micro-computed tomography (SXR-µCT) experiments more routinely available to users, with a rapid increase in demand given its tremendous potential in very diverse areas. In this work a survey of five different four-dimensional SXR-µCT experiments is presented, examining five different parameters linked to the evolution of the investigated system, and tackling problems in different areas in earth sciences. SXR-µCT is used to monitor the microstructural evolution of the investigated sample with the following variables: (i) high temperature, observing in situ oil shale pyrolysis; (ii) low temperature, replicating the generation of permafrost; (iii) high pressure, to study the invasion of supercritical CO in deep aquifers; (iv) uniaxial stress, to monitor the closure of a fracture filled with proppant, in shale; (v) reactive flow, to observe the evolution of the hydraulic p...

International Journal of Greenhouse Gas Control, 2017

Pore-scale distribution of supercritical CO 2 (scCO 2) exerts significant control on a variety of... more Pore-scale distribution of supercritical CO 2 (scCO 2) exerts significant control on a variety of key hydrologic as well as geochemical processes, including residual trapping and dissolution. Despite such importance, only a small number of experiments have directly characterized the three-dimensional distribution of scCO 2 in geologic materials during the invasion (drainage) process. We present a study which couples dynamic high-resolution synchrotron X-ray micro-computed tomography imaging of a scCO 2 /brine system at in situ pressure/temperature conditions with quantitative pore-scale modeling to allow direct validation of a pore-scale description of scCO 2 distribution. The experiment combines high-speed synchrotron radiography with tomography to characterize the brine saturated sample, the scCO 2 breakthrough process, and the partially saturated state of a sandstone sample from the Domengine Formation, a regionally extensive unit within the Sacramento Basin (California, USA). The availability of a 3D dataset allowed us to examine correlations between grains and pores morphometric parameters and the actual distribution of scCO 2 in the sample, including the examination of the role of small-scale sedimentary structure on CO 2 distribution. The segmented scCO 2 /brine volume was also used to validate a simple computational model based on the local thickness concept, able to accurately simulate the distribution of scCO 2 after drainage. The same method was also used to simulate Hg capillary pressure curves with satisfactory results when compared to the measured ones. This predictive approach, requiring only a tomographic scan of the dry sample, proved to be an effective route for studying processes related to CO 2 invasion structure in geological samples at the pore scale.

Journal of Geotechnical and Geoenvironmental Engineering, 2021

AbstractSoft viscoelastic biological products such as biopolymers and biofilms have recently garn... more AbstractSoft viscoelastic biological products such as biopolymers and biofilms have recently garnered significant interest as alternative biogrout materials for ground improvement because of their ...

Enhanced coal bed methane recovery (ECBM) is considered as a promising way to produce methane fro... more Enhanced coal bed methane recovery (ECBM) is considered as a promising way to produce methane from coal beds while storing carbon dioxide (CO2). The adsorption of CO2 on coal surfaces is known to render softening and swelling of coals, however, to what extent it will affect to permeability and P-wave velocity is still poorly understood. This study investigated the effect of swelling of coal induced by CO2 adsorption on permeability and P-wave velocity. It appeared that CO2 adsorption caused decreases in permeability and an increase in P-wave velocity. This study presents valuable laboratory test results of transport and geophysical properties and the obtained results provide a direct evidence of swelling effect caused by CO2 adsorption on coals.

GEOPHYSICS, 2021

Complex electrical conductivity is increasingly used to monitor subsurface processes associated w... more Complex electrical conductivity is increasingly used to monitor subsurface processes associated with microbial activities as microbial cells mostly have surface charges and thus electrical double layers. While highly saline environments are frequently encountered in coastal and marine sediments, there are limited data available on the complex conductivity associated with microbial activities under a high salinity condition. Therefore, we present the spectral responses of complex conductivity of sand associated with bacterial growth and biofilm formation under a highly saline condition of ∼1% salinity and ∼2 S/m pore water conductivity with an emphasis on relaxation behavior. A column test was performed, in which the model bacteria Shewanella oneidensis MR-1 were stimulated for cell growth and biofilm formation in a sand pack, while the complex conductivity was monitored from 0.01 Hz to 10 kHz. The test results show that the real conductivity increases in the early stage due to the m...