• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.17-26
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• 2019

In this study, the statistical characteristics of the resistance bias factors were analyzed using a high-quality field load test database, and the total resistance bias factors were estimated considering the soil uncertainty and construction errors for the application of the limit state design of aggregate pier foundation. The MLR model by Bong and Kim (2017), which has a higher prediction performance than the previous models was used for estimating the resistance bias factors, and its suitability was evaluated. The chi-square goodness of fit test was performed to estimate the probability distribution of the resistance bias factors, and the normal distribution was found to be most suitable. The total variability in the nominal resistance was estimated including the uncertainty of undrained shear strength and construction errors that can occur during the aggregate pier construction. Finally, the probability distribution of the total resistance bias factors is shown to follow a log-normal distribution. The parameters of the probability distribution according to the coefficient of variation of total resistance bias factors were estimated by Monte Carlo simulation, and their regression equations were proposed for simple application.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.197-213
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• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.763-768
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• 2018

In this study, glass fibers are fabricated via a continuous spinning process using manganese slag, steel slag, and silica stone. To fabricate the glass fibers, raw materials are put into an alumina crucible, melted at $1550^{\circ}C$ for 2 hrs, and then annealed at $600^{\circ}C$ for 2 hrs. We obtain a black colored glass. We identify the non-crystalline nature of the glass using an XRD(x-ray diffractometer) graph. An adaptable temperature for spinning of the bulk marble glass is characterized using a high temperature viscometer. Spinning is carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1109^{\circ}C$ to $1166^{\circ}C$, while the winder speed is in the range of 100rpm to 250rpm. We investigate the various properties of glass fibers. The average diameters of the glass fibers are measured by optical microscope and FE-SEM. The average diameter of the glass fibers is $73{\mu}m$ at 100rpm, $65{\mu}m$ at 150rpm, $55{\mu}m$ at 200rpm, and $45{\mu}m$ at 250rpm. The mechanical properties of the fibers are confirmed using a UTM(Universal materials testing machine). The average tensile strength of the glass fibers is 21MPa at 100rpm, 31MPa at 150rpm, 34MPa at 200rpm, and 45MPa at 250rpm.

• Journal of the Korea Organic Resources Recycling Association
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• v.26 no.4
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• pp.53-61
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• 2018

Anaerobic digestion (AD) is one of the most widely used process that can convert the organic fraction of waste activated sludge (WAS) into biogas. However, most researched actual methane yields of anaerobic digester (AD) on lab scale is lower than theoretical ones. Bioelectrochemical, anaerobic digester was used to increase methane yield from waste activated sludge. The influence of anaerobic digestion sludge and raw sludge mixing ratio (3:7, 5:5) on methane yield and organic matter removal efficiency were explored. As a result, when the mixing ratio of bioelectrochemical anaerobic sludge was 5:5 compared with 3:7, the highest methane yields were 294.2 mL $CH_4/L$ (0.63 times increase) and 52.5% (7.5% increase), the bioelectrochemical anaerobic digester(5:5) was more stable in the pH, t otal alkalinity and VFAs, respectively. These results showed that the increase in the mixing ratio of anaerobic digestion sludge was found to be effective for maintaining the stable performance of bioelectrochemical anaerobic digester.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.229-234
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• 2018

The glass-ceramic of $Li_2O-Al_2O_3-SiO_2$ system was synthesized by using $ZrO_2$, $ZrSiO_4$, $ZrOCl_2$ and $Zr(SO_4)_2$, which is a raw material of Zr serving as a nucleation agent. It was confirmed that Avrami parameter of these four glasses is over 3 for bulk crystallization. The glass synthesized by $ZrOCl_2$, and $Zr(SO_4)_2$ showed high melting quality during the melting process. It is also observed that the Zr component is uniformly distributed in the glass. Various characterizations was evaluated, including composition analysis and bending strength.

• Journal of Korean Society of Forest Science
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• v.107 no.4
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• pp.385-392
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• 2018

The slope stabilization analysis was performed by conducting survey and selecting the representative section in order to improve slope composition and management technology of masonry embankments in the quarry area, The mean slope of the masonry retain wall (A, B, C, D, E, F) was $38.5^{\circ}$, although the steep slope of the lowest slope (A) as $59^{\circ}$. The horizontal distance of the masonry embankments is 66.2 m and the slope height is 48.3 m. However, the inclination of the masonry embankments is relatively steep and visually unstable. The slope stability analysis for the slope stability analysis was taken into account during the drying and saturation. The slope stability analysis during saturation was performed by modeling the fully saturated slope. The strength constants of the ground were divided into two groups. The safety factor for dry period was 1.850 and the safety factor for rainy season was 1.333. The safety rate of dry period and rainy season was above 1.5 and 1.2. However, the weathered granite on the upper part of the masonry embankments at the time of heavy rainfall is considered to have a high risk of slope erosion and collapse. Therefore, it is considered necessary to take measures for stabilization through appropriate maintenance such as drainage installation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.519-534
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• 2019

Mechanized tunneling methods, including shield TBM, have been increasingly used for tunnel construction because of their relatively low vibration and noise levels as well as low risk of rock-falling accidents. In the excavation using the shield TBM, it is important to design penetration rate appropriately. In present study, both subsurface investigation data and shield TBM excavation data, produced for and during ${\bigcirc}{\bigcirc}{\sim}{\bigcirc}{\bigcirc}$ high-speed railway construction, were analyzed and used to compare with shield TBM penetration rates calculated using existing penetrating rate prediction models proposed by several foreign researchers. The correlation between thrust force per disk cutter and uniaxial compressive strength was also examined and, based on the correlation analysis, a simple prediction model for penetration rate was derived. The prediction results using the existing prediction models showed approximately error rates of 50~500%, whereas the results from the simple model proposed from this study showed an error rate of 15% in average. It may be said, therefore, that the proposed model has higher applicability for shield TBM construction in similar ground conditions.

• Design & Manufacturing
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• v.13 no.2
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• pp.17-21
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• 2019

In this study, selective laser sintered 3D printing mold core and metal core were used to investigate the difference of the thickness shrinkage from the gate of the injection molded part at a constant interval. SLS 3D printing mold core was made of nylon-based PA2200 powder and the metal core was manufactured by conventional machining method. As the PA2200 powder material has low strength, thermal conductivity and high specific heat characteristics compared with metal, molding conditions were set with the consideration of molten temperature and injection pressure. Crystalline resin(PP) and amorphous resin(PS) with low melting temperature and viscosity were selected for the injection molding experiment. Cooling time for processing condition was selected by checking the temperature change of the cores with a cavity temperature sensor. The cooling time of the 3D printing core was required a longer time than that of the metal core. The thickness shrinkage of the molded part compared to the core depth was measured from the gate by a constant interval. It was shown that the thickness shrinkage of the 3D printing core was 2.02 ~ 4.34% larger than that of metal core. In additions, in the case of metal core, thickness shrinkage was increased with distance from the gate, on the contrary, in the case of polymer core showed reversed aspect.

• Korean Journal of Heritage: History & Science
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• v.46 no.2
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• pp.206-219
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• 2013

This study aims to estimate firing temperature and physicochemical properties of the four clay bricks excavated from the Maritime Province of Siberia. Analysis result shows that the specimens are composed of clay, quartz and feldspar, and some specimens include carbonized organic materials which were probably added in order to enhance its physical strength in bricks. Major mineral components of the bricks are quartz, illite and clay minerals. The result identifying the existence of silimanite by XRD suggests that white material of the Koc 1 was painted for a certain purpose. Unlike most specimens which contained hematite, several samples contain Mullite. Such result suggests that some bricks were fired at high temperature. Furthermore, the results from TG analysis which does not display exothermic peak which appears at between $800^{\circ}C$ to $1,000^{\circ}C$ but display endothermic peak at $900^{\circ}C$ and it also confirms that they were exposed at $900^{\circ}C$ or higher.

• Korean Journal of Heritage: History & Science
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• v.43 no.3
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• pp.122-143
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• 2010

The Shilla Stone Monument in Jungseongri was found during the road-construction in Pohang. It has approximately two hundreds of letters inscribed on the surface of one side, and it is estimated to be older than Shilla Stone Monument in Naengsuri which had been known for the oldest stele in Shilla Period. This monument is made of fine to medium-grained biotite granite, while the Shilla Stone Monument in Naengsuri is made of fine-grained granodioritic porphyry bearing feldspar and amphibole phenocrysts. Both rock types of the monuments are interpreted to be cognate with biotite granite in Shinkwangmyeon, and with granodioritic porphyry in Gigyemyeon. They are characterized by xenolith and miarolitic cavity. Damage aspects in both monuments are discoloring, cracking and breaking. These damages do not cause structural instability of the monuments, but attenuate aesthetic value. Black and brown discoloring contaminants on the surface of the Jungseongri Monument contain a high amount of manganese and iron. As a result of ultrasonic test, both monuments were evaluated to be medium-weathered (MW), although the velocity of the Shilla Monument in Jungseongri was slightly lower than the Shilla Monument in Naengsuri. This is because the Monument in Juengseongri had been exposed to outdoor environment for long time until the discovery. It is necessary for Shilla Monuments to be protected by appropriately environmental control and management.