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뒷채움재의 내부마찰각 변화에 따른 철도교대의 안정성 및 공사비 비교
유충현(Chunghyun Yoo),최찬용(Chanyong Choi),양상범(Sangbeom Yang),박용걸(Yonggul Park) 한국지반신소재학회 2016 한국지반신소재학회 논문집 Vol.15 No.3
교대는 토압을 받는 구조체로 뒤채움의 재질 및 부설방법, 다짐정도, 배수시설 등에 따라 교대에 미치는 영향이 민감한 구조물이다. 하지만 보통 실무에서는 경험치인 내부마찰값을 30~35°를 적용하고 있는 실정으로 뒤채움재의 물성치값을 현실에 맞도록 합리적인 값의 설정이 필요하다고 할 수 있다. 본 논문에서는 교대높이 12m로 가정하고 직접기초의 교대를 최소안전율을 기반하여 절 ․ 성토 표준단면을 선정하여 내부마찰각의 변화에 따른 외적안정성분석와 부재력 검토하여 공사비를 비교하였다. 그 결과 내부마찰각에 따라 교대단면 축소 등으로 인한 공사비용 절감효과는 약 2.2%~8.4% 감소하였다. The railway bridge abutment subjected to the lateral earth pressure is a sensitive structure that is affected by backfill materials, installation methods, compaction, and drainage system and so on. The several design loads for the bridge abutment design consist of traffic loading on bridges and vertical & lateral force due to surcharge load at backfill. Especially, the lateral earth pressure of design load components is important and considered in the design of geotechnical engineering structure such as bridge abutment wall. The determination of cross section for abutment is finally determined with calculating external stability and member force of abutment wall structures. In this study, the abutment wall height is 12m and the optimal cross section of abutment wall has been determined that satisfies an external stability for abutment structure through friction angles of 35, 40, and 45 degrees of backfill materials. The external stability and member force of abutment wall with friction angle of backfill materials and were calculated and construction cost of each abutment wall structures was compared. It found that the construction cost was reduced from 2.2 to 8.4% with friction angle of backfill materials.
유충현(Yoo Chung-Hyun),최찬용(Choi Chan-Yong),김대상(Kim Dae-Sang) 한국철도학회 2007 한국철도학회 학술발표대회논문집 Vol.- No.-
The purpose of a railway track is to provide a smooth surface for safe and economical train transportation. The performance of the track results from a complex interaction of the track and subgrade components in response to train loading and environmental actions. In the past, the role of subgrade as the track foundation were not recognized adequately. There are insufficient information and inadequate methods for subgrade design, assessment and improvement. This situation has survived for a long time largely because a subgrade defect can often be adjusted by adding more ballast under the ties or applying more frequent track maintenance. Therefore, the application of reinforced roadbed technology will be expected to increase in the future. The reinforced roadbed thickness is set depending on subgrade reaction modulus(K₃?) in the condition of upper subgrade through PBT in both conventional railroad and KTX railroads. As train velocity (V), train passing tonnage (N), and train axial load (P) are not considered in design, the roadbed thickness could be overestimated (or underestimated). Therefore, in this study has proposed a determination method of reinforced roadbed thickness using design chart made by resilience modulus and properties of earthwork materials.
Si 기판 위에 형성된 InAs 양자점의 열처리에 의한 표면 상태의 변화
유충현,Yoo, Choong-Hyun 한국전기전자재료학회 2007 전기전자재료학회논문지 Vol.20 No.10
Effect of high-temperature annealing on morphology of fully coherent self-assembled InAs quantum dots' grown on Si (100) substrates at $450^{\circ}C$ by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) was investigated by atomic force microscopy(AFM). When the dots were annealed at 500 - 600$^{\circ}C$ for 15 sec - 60 min, there was no appreciable change in the dot density but the heights of the dots increased along with the reduction in the diameters. In segregation from the InAs quantum dots and/or from the 2-dimensional InAs wetting layer which was not transformed into quantum dots looked responsible for this change in the dot size. However the change rates remained almost same regardless of annealing time and temperature, which may indicate that the morphological change due to thermal annealing is done instantly when the dots are exposed to high temperature annealing.
Nucleation Layer의 표면 거칠기가 GaAs 기판 위에 성장된 InP 에피층의 품질에 미치는 영향
유충현,Yoo, Choong-Hyun 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.8
Heteroepitaxial InP films have been grown on GaAs substrates to study the effects of the nucleation layer's surface roughness on the epitaxial layer's quality. For this, InP nucleation layers were grown at $400^{\circ}C$ with various ethyldimethylindium (EDMIn) flow rates and durations of growth, annealed at $6200^{\circ}C$ for 10 minutes and then InP epitaxial layers were grown at $550^{\circ}C$. It has been found that the nucleation layer's surface roughness is a critical factor on the epitaxial layer's quality. When a nucleation layer is grown with an EDMIn flow rate of 2.3 ${\mu}mole/min$ for 12 minutes, the surface roughness of the nucleation layer is minimum and the successively grown epitaxial layer's qualities are comparable to those of the homoepitaxial InP layers reported. The minimum full width at half maximum of InP (200) x-ray diffraction peak and that of near-band-edge peak from a 4.4 K photoluminescence are 60 arcmin and 6.33 meV, respectively.
대기압 MOCVD 시스템을 이용하여 Si 기판 위에 자발적으로 형성된 InAs 양자점에 대한 연구
유충현,Yoo, Choong-Hyun 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.6
Fully coherent self-assembled InAs quantum dots(QDs) grown on Si (100) substrates by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) were grown and the effect of growth conditions such as growth rate and growth time on quantum dots' morphology such as densities and sizes was investigated. InAs QDs of 30 - 80 nm in diameters with densities in the range of (0.6 - 1.7) x $10^{10}\;cm^{-2}$ were achieved on Si substrates and InAs layer was changed from 2 dimensional growth to 3 dimensional one at a nominal thickness less than 0.48 ML. This is attributed to the higher ambient pressure of APMOCVD suppressing of In segregation from the 2 dimensional InAs layer. This In segregation looked to disturb the dot formation especially when the growth rate was low so that the dots became less dense and bigger as the growth rate was lower.