• Journal of the Society of Disaster Information
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• v.20 no.1
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• pp.169-176
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• 2024

Purpose: In this paper, an experimental study was conducted to analyze the difference in shear strength caused by the problem of excluding coarse particles due to the size of the test specimen in the direct shear test. Method: A large-scale direct shear test was conducted on three weathered soils containing coarse aggregates with a maximum diameter of 50mm. In addition, a small-scale direct shear test was performed using a sample with a maximum diameter of 5 mm, excluding coarse aggregates. Result: In the case of the small-scale direct shear test, compared to the results of the large-scale direct shear test containing large particles, the internal friction angle was about 2.3% smaller, and there was no significant difference. In terms of cohesion, compared to the large-scale direct shear test, the small-scale direct shear test derived about 80.3% smaller value, showing a relatively large difference. Conclusion: In the large-scale direct shear test, it was analyzed that the coarse particles had a greater impact on the cohesion than the internal friction angle. Therefore, granite weathered clay containing coarse particles is judged to have the same shear strength as the cohesive force that is not affected by vertical stress. In this study, it was analyzed that the small-scale direct shear test, which excludes the coarse particles that are commonly used, provides results on the safety side by excluding the effect of coarse particles.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.48-54
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• 1996

가압경수로의 부분충수 운전중 RHR 계통의 기능상실시 사고완화를 위해 가압기 manway와 증기 발생기 출구공동 manway를 동시에 개방한 경우에 대한 실험결과를 CATHAHR2 코드를 이용하여 해석하였다. 해석을 통해 이 경우에 발생하는 물리적 현상을 이해하고 이와 같은 과도기에 대해 코드 예측능력을 평가하므로 써, 실제 원전에서 사고시 적절한 사고대응 방안을 강구하는데 참고가 될 수 있도록 해석적 근거를 제시하고자 한다. 연구결과 CATHARE2 코드는 실험을 통해 관측된 주요 물리적 현상들을 타당하게 예측하였으나, 가압기와 밀림관의 DP를 과대 예측하여 원자로 상부공동의 최대압력을 실험보다 약 7kPa 높게 예측하였다. 노심 노출시간도 노심에서 기포율 분포를 비현실적으로 예측하여 실험보다 약 500초 지연되었다. 실험과 코드의 모의결과를 통하여 노심 노출은 중력주입에 의한 냉각수 보충만으로 충분히 회복될 수 있음을 확인하였다. CATHARE2 코드는 비록 상세한 현상들에 대해 다소 불확실성을 내포하였으나, 전반적인 거동분석에는 타당한 것으로 판단된다. CATHARE 코드는 노심에서 계면 마찰력을 줄임으로써 노심의 차압을 개선할 수 있었고, guide 튜브의 위치를 고온관 중심선과 일치시켜 guide 튜브내 액체의 hold-up 기간을 개선할 수 있었으며, 가압기의 계면 마찰력을 증가시켜서 밀림관에서 "plug and clearing" 현상을 모의할 수 있었다.모의할 수 있었다.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.177-185
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• 2000

An experimental research to evaluate the slip coefficients of high-strength friction-type bolt connection of weathering steel plate has been performed in this paper. The test specimens with mill scale or shot blast had been exposed in open air during 3 and 6 months and cleaning of rust surface by hand brushing, power tool brushing and no cleaning was considered. The relaxation of bolt clamping force had also been measured during 600 hours. It was found that slip coefficients increased to the value over 0.6 with exposure except mill scale surface by power tool brushing. The relaxation of bolt tension force in exposed specimens also increased and maximum value reached to about 10%.

• Journal of Energy Engineering
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• v.7 no.2
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• pp.163-171
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• 1998

Degradation of polymer additives is enhanced at higher temperature of the test solutions. The degradation of Co-polymer solution was investigated experimentally in a closed loop at the temperature of 6$0^{\circ}C$ and 8$0^{\circ}C$ with various polymer concentrations of 100, 200, 400, 600 ppm in order to see the effect of temperature and polymer concentration with time. The degradation effect were found to be more dependent on temperature than mechanical shear. The friction factor versus Reynolds number curves show that in the range of Reynolds number number 50,000~150,000 the friction was decreased as Reynolds number increased and the friction of solution at low temperature approached to Virk's maximum drag reduction asymptote. For constant flowrates and temperatures the degradation effect was found to be less likely in higher polymer concentration. For constant flowrates and polymer concentrations the degradation rates are affected mainly by temperature. At the temperature of 8$0^{\circ}C$ and polymer concentration of 100 ppm, drag reduction effect was disappeared after 4 hours. However, this thermal degradation could be avoided with additional materials such as surfactants which are supposed to enhance the bonding forces between polymer molecules.

• Journal of the Korean Geosynthetics Society
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• v.7 no.3
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• pp.17-24
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• 2008

This study is conducted to investigate the possibility of the utilization of the mixed soil formed by mixing stone sludge, bentonite, and residual soil as a soil sealant sustaining both stability and capacity in the barrier system. A series of tests were performed on the mixed soils to evaluate basic properties such as compaction, compressive strength, permeability and CBR of these materials. The results indicates that as the stone sludge content increases, the optimum moisture content increases a little, but the maximum dry density decreases. The compressive strength and CBR decrease, and the cohesion, internal friction angle and expansion ratio increase. When the bentonite content increases, the maximum dry density decreases, and the optimum moisture content, compressive strength and cohesion, internal friction angle, CBR and expansion ratio increase. Mixing ratio of the mixed soil contained with the stone dust more than 10% and the bentonite less than 10% satisfies the standard of the permeability coefficient as the soil sealant.

• 한국해양학회지
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• v.25 no.1
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• pp.26-35
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• 1990

Sound velocities and attenuation coefficients of marine surface sediments were calculated from insitu acoustic experiments on 4 nearshore areas off Pohang, Pusan Yeosu, and Kunsan around the Korean Peninsula. The relationship between these values and physical properties of sediments was examined and attenuation mechanism was analysed using the estimated gas content. Sound velocities and attenuation coefficients ranging from 1470 to 1616 m/sec and 0.0565 to 0.6604 dB/kHz-m, respectively, are well related to sediment types. The attenuation coefficient is maximum in coarse silts, and the sound velocity increases with density. The gas content estimated less than 8 ppm increases with the decreasing sediment grain size. When the sediment size is greater than fine sand, sound attenuation is mostly due to friction losses, and probably negligible viscous loss remains unchanged with the varying physical properties of sediments. The maximum attenuation in coarse silts result from both friction loss and cohesion of finer sediments between the contacts of silt grains. The cohesion begins to be the dominant dissipative process with decreasing grain size from medium and fine silts.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.34-39
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• 2016

Structural behaviour of PSC box bridge, on which KTX train runs, is analysed up to 500 km/h speed considering 12 stages track irregularity and interaction between bridge and vehicle. To evaluate wheel forces and rotations of vehicle, lateral wheel forces, derail factor and offload factor calculated on the track combining the bridge and 170 m normal track are compared with existing allowed limits. Maximum longitudinal displacement and accumulated sliding distance of the brige bearings for simply supported and 2 span continuous PSC bridges are presented by each running speeds. Long-term friction tests based on EN-1337-2 are conducted between PTFE and DP-mate plates. Finally, the long-term friction tests are proposed to consider the increasing speed of next generation high-speed train.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.189-193
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• 2010

RMA-2, Telemac-2D, River2D 등 기존의 대부분 국내외 상용모형에서는 내부 경계인 하천구조물과 외부 경계인 측벽에서의 경계조건을 활동조건(slip condition)으로 가정하여 흐름장을 계산하였다. 그러나 실제로 벽면에서는 마찰력에 의해 흐름이 존재하지 않는 무활조건(no slip condition)이 물리적으로 타당하다. 따라서 본 연구에서는 내부구조물인 교각이 존재하는 영역에서의 수평 2차원 유속분포를 구하기 위해 천수방정식을 Galerkin법과 Newton-Raphson법에 의해 이산화한 수치모형을 개발하였다. Yulistiyanto 등(1998)이 수치모의 및 수리실험에 사용한 조건을 채택하여 벽면에서의 접선방향 유속이 존재하는 활동조건과 벽면에서 유속이 없는 무활조건을 부여하고 교각을 포함한 수로에서 유속, 수위 및 전단분포를 해석하였다. 활동경계조건을 적용한 경우 교각 표면을 따라 큰 유속이 분포하고 후면에서도 관성력에 의해 흐름방향 유속이 두드러지게 나타났으나 무활조건을 적용한 경우 교각 후면에서 와가 형성되고 후류현상이 두드러지게 나타났다. 무활조건을 적용한 경우 교각 전면부에서는 선수파(bow wave)가 4 cm정도 높게 나타났으며 교각 측면부에서는 2 cm 높게 나타났다. 반면 교각 후면에서는 후류의 영향으로 수면이 2 cm 낮게 분포하였다. 교각부에 작용하는 전단력을 분석한 결과 무활조건을 적용한 경우가 활동조건을 적용한 경우에 비해 최대 6배 높은 전단력이 나타났다.

• Journal of the Korean GEO-environmental Society
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• v.11 no.6
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• pp.47-55
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• 2010

The recycled fine aggregates were mixed with weathered granite soils typically used for fill materials and tested engineering properties, physical properties, and compaction characteristics according to the mixing ratio of the mixed soils. The results of this study were as follows. For the results of A-type compaction test, the recycled fine aggregates showed low effects compared to the weathered soils, but the mixed soils which were mixed with the weathered granite soils and the recycled fine aggregates showed good compaction effects. Especially, the mixing ratio of 70:30 by weight showed for maximum compaction result. From the results of the direct shear test, the cohesion was ince csed according to proportion of the weathered granite soils. The weathered granite soils neared the optimum moisture content showed for maximum shear strength paramcoers, while the cohesion of the mixed soil was relatively ince csed in the wet side of the optimum moisture content. This trend was seemed to remained cence composition in the recycled fine aggregates. The internal friction angle of the recycled fine aggregates and the mixed soils showed maximum value near dry side of the optimum moisture contents. And the internal friction angles of the mixed soils were increased according to higher proportion of the recycled fine aggregates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.213-220
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• 2008

A study on cemented sand reinforced with short fibers was carried out to improve its unconfined compressive strength and brittle behavior. Nak-dong River sand was mixed with Portland cement and polyvinyl alcohol (PVA) fibers. A PVA fiber widely used for concrete reinforcement is randomly distributed into cemented sand. Nak-dong River sand, cement and fibers with optimum water content were compacted in 5 layers and then cured for 7 days. The effect of fiber reinforcement rather than cementation was emphasized by using a small amount of cement. Weakly cemented sand with a cement/sand ratio less than 8% was fiber-reinforced with different fiber ratios and tested for unconfined compression tests. The effect of fiber ratio and cement ratio on unconfined compressive strength was investigated. Fiber-reinforced cemented sand with 2% cement ratio showed up to six times strength to non-reinforced cemented sand. Because of ductile behavior of fiber-reinforced specimens, an axial strain at peak stress of specimens with 2% cement ratio increases up to 7% as a fiber ratio increases. The effect of 1% fiber addition into 2% cemented sand on friction angle and cohesion was analyzed separately. When the fiber reinforcement is related to friction angle increase, the 8% of applied stress transferred to 1% fibers within specimens.