• The Journal of Engineering Geology
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• v.14 no.3 s.40
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• pp.301-311
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• 2004

This study is suggested a new dielectric tracer test method to understand geological structure of porous media and groundwater flow to use the dielectric constant which is one of electrical special quality of various geological materials. To measure their parameters, tracer material is made an ethanol mixing liquid(EML) having a same specific gravity of water. Also, soil materials are prepared a dielectric tracer test using the FDR system that could measure dielectric constant for saturated standard sand and river sand layers which have different initial porosity. To compare with their results, we discussed with the concentration variation of saline water having a saline concentration $3\%$ which is general tracer material by using the electro multi-meter system in the laboratory or field test. In two tracer experiment results, EML tracer test could confirm definitely EML concentration variation from each saturated soil layer as standard and river sands. However, tracer test of saline water $3\%$ concentration could not confirm permeating movement of water by degree of salinity change because these are settled at lower part column in a whole column area continuously. These causes are that specific gravity of saline water is heavier than water. That is, it could know that deposition of saline water is composed of lower part of soil column continuously independently of the direction of water into saturated soil material.

• The Journal of Engineering Geology
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• v.15 no.2 s.42
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• pp.105-121
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• 2005

Most of the landslides triggered by intensive rainfall on natural slope occur serious damages of human beings and properties. There have been many landslides since 1991 in Gyeonggi province. The influential factors are rainfall, topography, geology and soil properties. There were 660 landslides occurred by intensive rainfall as much as 250mm at Yongin and Anseong area from Tuly 19th to luly 21st,1991 This study surveyed location, topography, geology, geometry of the landslide and rainfall at the area and analyzed occurrence characteristics of the landslides. Most of the landslides occurred on the soil layer above the bed rock. They showed changes of landslide types from translational slides at the head part to flow at the central part. The landslides have relatively small magnitude of which length is shorter than 50m. In order to identify characteristics of landslides dependent on soil conditions, geotechnical properties of soil were evaluated by laboratory tests using soil samples which were collected on slided area and not-slided area. Soil properties of the slided area show high percentage of coarse material such as gravel and sand. However, soil of the not-slided area is mainly composed of fine material such as silt and clay. Permeability coefficients of the slided area are higher than those of the not-slided area.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.245-253
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• 2017

Vietnam CFBC fly ash has high CaO content and can be used as a solidification agent for soft ground improvement. However, most fly ash is treated as landfill or waste. In order to utilize fly ash as a solidification agent for soil improvement, the characteristics of fly ash must be accurately determined. In this study, laboratory tests were conducted on fly ash from four CFBC power plants to evaluate the utility of Vietnam fly ash as a solidification agent. As a result of analyzing the physical properties, it was analyzed that all four samples were suitable as material for solidification agent and have suitable particle size for the improvement of soft ground. As a result of analysis of chemical characteristics, it was analyzed that the fly ash of one place could be used as a solidification agent because of the high content of free-CaO. The remaining three fly ash was not suitable for use as a solidification agent due to low Free-CaO content. However, it has a chemical composition similar to that of general fly ash in Korea, so it can be recycled in various ways.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.401-406
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• 2020

NOx (nitrogen oxide) in the exhaust gas engines causes severe air pollution. NOx is produced under high-temperature combustion conditions. EGR (exhaust gas recirculation) is normally used to reduce the combustion temperature and NOx production. As the EGR ratio increases, the NOx level becomes low. On the other hand, an excessively high EGR ratio makes the combustion unstable resulting in other air pollution problems, such as unburned hydrocarbon and higher CO levels. In this study, the improvement of fuel droplets moving by the radiation of sonic waves was studied for the stable combustion using analytic and experimental methods. For the analytical study, the effects of the radiation of a sonic wave on the fuel droplet velocity were studied using Fluent software. The results showed that the small droplet velocity increased more under high-frequency sonic wave conditions, and the large droplet velocity increased more under low-frequency sonic wave conditions. For the experimental study, the combustion chamber was made to measure the combustion pressure under the sonic wave effect. The measured pressure was used to calculate the heat release rate in the combustion chamber. With the heat release rate data, the heat release rate increased during the initial combustion process under low-frequency sonic wave conditions.

• International Journal of Highway Engineering
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• v.3 no.3 s.9
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• pp.119-133
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• 2001

The stiffness of chemcrete modified asphalt mixtures increase rapidly with time in the presence f oxygen and high temperature, Sometimes the asphalt pavements that have chemcrete modified asphalt mixture applied on the surface none show premature cracking because of the excessive increase in the stiffness f the asphalt mixtures. To mitigate this premature cracking, the chemcrete modified mixtures have been used as a base course material. In this study, the performance of the chemcrete modified asphalt binder and mixtures are investigated through a course of various laboratory tests including dynamic shear rheometer and bending beam rheometer tests for binders and uniaxial tensile fatigue, wheel tracking, and moisture damage tests for the mixtures. And also the resilient modulus of the conventional and chemcrete modified mixtures are compared based on the test results conducted on the specimens obtained from various in-situ test sections. It can be concluded from the tests results that the chemcrete modified mixtures show better rutting resistance than conventional mixtures. The chemcrete modified mixtures may have low temperature cracking when it is applied in the cold region. The stiffness of chemcrete modified mixtures is approximately 50 percent higher than that of conventional mixtures more than two years after the chemcrete modified mixture was applied in the base course.

• Fire Science and Engineering
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• v.20 no.3 s.63
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• pp.65-70
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• 2006

From the beginning of the construction stage, the fire protection regulation for the nuclear power plants conforms to the design requirements for the acquisition of the license permit. This regulation is based on the plant status of the normal operation, but it is not enough to be used as an application standard for fire protection at the transient mode of the plant and the outage time for refueling as well as for the plant decommissioning. While the advanced fire protection requirement that has been developed in America recently suggests the performance-based requirement and management rule applicable to the overall life time of the plant, it simply represents the conceptual application. It means that it can not be treated as appropriate standards because it does not deal with the qualitative and quantitative approach in specific ways. By the way, with the use of the performance-based fire risk analysis, the dynamic behavior of the heat and smoke at the fire compartment of the nuclear power plants can be analyzed and the thermal effect to the safety-related equipment and cables can be evaluated as well. At this paper, it suggests the ways to change the applicable fire protection regulations and the required evaluation items for the fire risk resulted from the plant configuration change with an intent to introduce the state-of-the-art quantitative fire risk analysis technology at the domestic nuclear power plants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.246-252
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• 2020

Safety accidents have been reported due to falling accumulated snow from cables of cable-supported bridges. In addition to the direct damage caused by falling snow, secondary damage, such as traffic accidents, can occur. Various methods have been proposed to prevent these accidents, but there are still problems in safety and practicality. In this study, a cable robot type was selected as one of the active methods for removing accumulated snow on cables. An attempt was made to increase the climbing ability of the robot to improve the efficiency of snow removal. In addition, the available range of cable diameter for the robot can be adjusted flexibly to be applied to cables used in the field. A high-resolution camera was also installed to check the surface condition of the cable in real time to increase the utility, and be used as a cable inspection robot. A three-axis accelerometer and a tension conversion algorithm were added to measure the tension force of cables. To verify the performance, indoor and field experiments were conducted, and future improvements for the inspection robot were proposed.

• Fire Science and Engineering
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• v.21 no.3
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• pp.15-23
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• 2007

In the events of a fire in the residential building, highly flammable polyurethane foam sofa produce toxic smokes. In this type of fire, the residents of the building can be gotten into the difficulties of evacuating from the fire places or may be to death due to a lot of hot toxic gases. In this study, CFD simulations were carried out to study the effects of the openings of stairwell on the fire characteristics of fire room and stairwell. Also, analysis of fire hazard based on the tenability limits of fire and FED(fractional effective dose) was performed to evaluate the life safety of the residents of the building. In the fire room, maximum temperature was about $290^{\circ}C$, maximum CO concentration was about 4,740 ppm, and the time to incapacitation of residents in fire room was about t=144 s. In the stairwell, temperature and CO concentration in the condition of openings to be open were even lower than those in it to be closed. Time to the tenability limit with respect to smoke visibility in the stairwell with openings, which was open, was shorter than that of it without openings to be open. It has been shown from this study that opening the stairwell openings is able to decrease the fire hazards to the life safety in the multi-story residential building fire.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.19-25
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• 2009

The current study developed light-weighted mixed soil that can solve problems related with soft soil such as ground subsidence, sliding and lateral displacement of ground. By reducing weight of reclaimed soil through mixing phosphogypsum and recycled EPS beads with the weathered granite soil. A series of geotechnical laboratory tests including physical index test, compaction test, CBR test, and direct shear test were performed and engineering properties were reviewed in order to assess applicability of the light-weighted mixed soil for roads and abutment and various back-filling materials at the reclamation area. Based on the laboratory test results, it was found that the maximum dry unit weight of the light-weighted soil ranges $14.32{\sim}15.79kN/m^3$ and the optimum water content ranges 21.91~24.23%, which means there is 11~19.3% weight decrease effect when comparing with general weathered granite soil. Also it was found that the corrected CBR value ranges 10.4~18.4% satisfying the domestic regulations on road subgrade and back-filling material. In addition, as for shear strength parameter, cohesion ranges 10.79~18.64 kPa and internal frictional angle ranges $35.4{\sim}37.2^{\circ}$, which are similar with those of general construction soil and back-filling material used in Korea. So it can be concluded that light-weighted mixed soil with phosphogypsum can be used effectively for soft reclamation ground as actual filling material and back-filling material. From the current study, it was found that light-weighted mixed soil with phosphogypsum has not only weight reduction effect, but also has no special problems in shear strength and bearing capacity. Therefore, it is expected that phosphogypsum can be recycled in bulk as road subgrade and back-filling material at the reclamation area.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.103-103
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• 2015

유류유출사고와 같이 하천 수표면의 흐름에 따라 이동 확산하는 부유성 오염물질의 혼합해석을 위해 많은 연구자들은 입자추적모형을 사용한 혼합모의를 수행해왔다. 입자추적모형에서 오염물질의 혼합은 평균 유속 분포에 의한 결정론적인 이동과 난류유동에 의한 무작위적인 혼합으로 나타내며, 난류혼합에 의한 수평확산은 난류확산계수로 조절한다. 따라서 표면흐름에 의한 난류확산계수의 산정을 위해 많은 연구자들은 부유성 입자를 이용한 실내실험을 수행하여 수평확산계수를 산정했고(Engelund, 1969; Cederwall, 1971), 최근에는 GPS의 발전으로 인해 해양영역에서 GPS를 장착한 표면부자를 활용한 확산실험을 통해 수평확산계수를 산정한 바 있다(Kjellson and $D{\ddot{o}}{\ddot{o}}s$, 2012; Alpers 등, 2013). 하천수질오염사고의 약 43.5%가 유류유출에 의한 것이며(환경부, 2013), 이에 따라 표면흐름에 의한 오염물질 혼합해석이 필요하나, 하천에서 수평확산계수 산정을 위한 현장실험연구는 부족한 상황이다. 따라서 본 연구에서는 낙동강 본류에서 GPS부자를 이용한 입자추적실험을 수행하여 표면흐름에 의한 확산계수를 산정했다. GPS부자를 이용한 입자추적실험은 낙동강의 강정고령보 하류와 구미보 하류의 각각 세 지점에서 수행되었다. GPS부자는 바람에 의한 교란을 최소화하기 위해 지름 10 cm의 구형으로 제작하였으며 시범테스트를 통해 입자의 주 궤적 변화가 크지 않은 지점에 GPS부자를 투입했다. GPS부자는 오염물질의 사고유출을 가정하여 한 지점에 투입했고 GPS부자 사이의 간섭을 최소화하기 위해 25 ~ 35개의 GPS부자를 이용했다. 표면흐름에 의해 이동하는 부자의 위치는 GPS에 시계열로 저장됐고 ADCP를 이용하여 실험당시의 수리량을 측정했다. 입자위치의 시계열자료로부터 GPS부자의 확산범위의 시간변화를 계산했고 단순 모멘트법을 이용하여 종, 횡 방향 확산계수를 계산했다. 그 결과, 종 방향 확산계수는 $0.003{\sim}0.041m^2/s$로 계산되었고 횡 방향 확산 계수는 $0.001{\sim}0.012m^2/s$로 계산되어, 흐름방향의 유속성분에 의한 확산이 지배적인 것으로 나타났다. 지류 합류부에서는 이송이 지배적인 혼합이 발생되었고(Pe>1) Pe의 증가에 따라 수평확산계수가 감소되었다. 25~35개 GPS부자 궤적의 앙상블 평균으로부터 계산한 Integral time scale은 모멘트법으로부터 계산한 종, 횡 방향 확산계수와 비례하는 것으로 나타나, Taylor(1921)의 이론과 일치했다. 또한 실험수로에서 수행된 기존연구결과와 비교한 결과, 하폭 대 수심비, 마찰항의 증가에 따라 수평확산계수가 증가하는 경향을 나타내었다.