• 한국지반공학회논문집
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• 제39권11호
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• pp.23-31
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• 2023

콘크리트 궤도의 침하는 고속열차의 안전한 운행을 크게 저해할 수 있으며 복구에 상당한 비용이 소요되므로 최근 큰 문제로 대두되고 있다. 침하의 가장 큰 원인 중 하나는 터널공사의 부산물로 발생하는 암석재료를 적정한 입도분를 가진 토사 혼합 없이 하부노반 성토에 사용하기 때문으로 보고되고 있다. 본 논문에서는 암석재료로 성토된 하부노반의 부분 보강으로 인한 침하억제 효과를 수치해석으로 평가하였다. 하부노반에 일정하게 배치된 기둥 형태의 보강 영역은 상부노반에 지반아칭을 유발하게 되며 성토하중이 보강된 영역에 집중하게 되어 침하가 억제되는 효과가 있다. 유한요소해석을 통하여 보강된 영역의 크기, 강성, 간격이 하부노반의 침하억제에 미치는 효과를 평가하였으며, 해석 결과를 토대로 침하를 허용치 이내로 억제하기 위한 최소 보강 간격을 결정하는 설계 방법을 제안하였다.

• 지질공학
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• 제19권3호
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• pp.287-294
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• 2009

퇴적암인 셰일이나 이암이 광역변성작용을 받아 형성된 운모편암들이 분포하는 지역에서 도로나 철도 등의 건설 시 발생하는 사면은 이들 암석들이 가지는 층리나 엽리 혹은 절리와 같은 불연속면들의 발달 방향과 도로나 철로의 진행 방향의 조건에 따라 자주 사면의 붕괴 등에 의한 시공 상 어려움이 발생하고 있다. 운모편암은 변성작용 과정에서나 변형작용 과정을 거치면서 형성된 엽리 및 벽계면들이 사면에 영향을 미친다. 일반적으로 운모편암 중에는 팽창성광물인 스멕타이트. 버미쿨라이트, 몬모리오나이트 등이 함유 되어 사면이 형성된 후 지표에 노출되면서 공기 중의 수분과 반응하여 사면의 안정성에 불리하게 작용한다. 경부 고속철도 건설 시 수원부근의 운모 편암 지대에서 터널 시공 중 터널의 종점부 사면에서 붕괴가 일어난 곳의 지반 조건 및 붕괴 원인을 분석하였다. 이곳은 1-5cm의 절리 간격을 가지며 역단층과 주향이동단층 들이 발당한다. 이로 인해 사면이 심히 파쇄 되어 있으며 시추 코어에서도 전 구간의 RQD가 0-20%값을 가진다.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1618-1629
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• 2003

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20$^{\circ}$, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

• Wind and Structures
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• 제24권5호
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• pp.501-528
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• 2017

In this work, wind tunnel tests of pressure measurements are carried out to assess the global aerodynamic interference factors, the local wind pressure interference factors, and the local lift spectra of an square high-rise building interfered by an identical cross-sections but lower height building arranged in various relative positions. The results show that, when the interfering building is located in an area of oblique upstream, the RMS of the along-wind, across-wind, and torsional aerodynamic forces on the test building increase significantly, and when it is located to a side, the mean across-wind and torsional aerodynamic forces increase; In addition, when the interfering building is located upstream or staggered upstream, the mean wind pressures on the sheltered windward side turn form positive to negative and with a maximum absolute value of up to 1.75 times, and the fluctuating wind pressures on the sheltered windward side and leading edge of the side increase significantly with decreasing spacing ratio (up to a maximum of 3.5 times). When it is located to a side, the mean and fluctuating wind pressures on the leading edge of inner side are significantly increased. The three-dimensional flow around a slightly-shorter disturbing building has a great effect on the average and fluctuating wind pressures on the windward or cross-wind faces. When the disturbing building is near to the test building, the vortex shedding peak in the lift spectra decreases and there are no obvious signs of periodicity, however, the energies of the high frequency components undergo an obvious increase.

• Wind and Structures
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• 제30권6호
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• pp.617-631
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• 2020

Wake-induced aerodynamics of yawed circular cylinders with smooth and grooved surfaces in a tandem arrangement was studied. This pair of cylinders represent sections of stay-cables with smooth surfaces and high-voltage power conductors with grooved surfaces that are vulnerable to flow-induced structural failure. The study provides some insight for a better understanding of wake-induced loads and galloping problem of bundled cables. All experiments in this study were conducted using a pair of stationary section models of circular cylinders in a wind tunnel subjected to uniform and smooth flow. The aerodynamic force coefficients and vortex-shedding frequency of the downstream model were extracted from the surface pressure distribution. For measurement, polished aluminum tubes were used as smooth cables; and hollow tubes with a helically grooved surface were used as power conductors. The aerodynamic properties of the downstream model were captured at wind speeds of about 6-23 m/s (Reynolds number of 5×10⁴ to 2.67×10⁵ for smooth cable and 2×10⁴ to 1.01×10⁵ for grooved cable) and yaw angles ranging from 0° to 45° while the upstream model was fixed at the various spacing between the two model cylinders. The results showed that the Strouhal number of yawed cable is less than the non-yawed case at a given Reynolds number, and its value is smaller than the Strouhal number of a single cable. Additionally, compared to the single smooth cable, it was observed that there was a reduction of drag coefficient of the downstream model, but no change in a drag coefficient of the downstream grooved case in the range of Reynolds number in this study.

• Geomechanics and Engineering
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• 제19권6호
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• pp.485-498
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• 2019

Pre-tensioned rock bolts can be classified into fully anchored, lengthening anchored and point anchored bolts based on the bond length of the resin or cement mortar inside the borehole. Bolts in varying anchoring methods may significantly affect the supporting effect of surrounding rock around a tunnel. However, thus far, the theoretical basis of selecting a proper anchoring method has not been thoroughly investigated. Based on this problem, 16 schemes were designed while incorporating the effects of anchoring length, pretension, bolt length, and spacing, and a systematic numerical experiment was performed in this paper. The distribution characteristics of the stress field in the surrounding rock, which corresponded to various anchoring scenarios, were obtained. Furthermore, an analytical approach for computing the active and passive strengthening index of the anchored surrounding rock is presented. A new fully anchoring method with pretension and matching technology are also provided. Then, an isolated loading model of the anchored surrounding rock was constructed. The physical simulation test for the bearing capacity of the model was performed with three schemes. Finally, the strengthening mechanism of varying anchoring methods was validated. The research findings in this paper may provide theoretical guidelines for the design and construction of bolting support in tunnels.

• Wind and Structures
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• 제26권2호
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• pp.57-68
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• 2018

Wind tunnel tests are conducted to investigate wake-induced vibrations of two circular cylinders with a center-to-center spacing of 4 diameters and attack angle varying from $0^{\circ}$ to $20^{\circ}$ for Reynolds numbers between 18,000 and 168,800. Effects of structural damping, Reynolds number, attack angle and reduced velocity on dynamic responses are examined. Results show that wake-induced vortex vibrations of the downstream cylinder occur in a wider range of the reduced velocity and have higher amplitudes in comparison to the vortex-induced vibration of a single circular cylinder. Two types of wake-induced instability phenomena with distinct dynamic characteristics are observed, which may be due to different generation mechanisms. For small attack angles like $5^{\circ}$ and $10^{\circ}$, the instability of the downstream cylinder characterizes a one-degree-of-freedom (1-DOF) oscillation moving in the across-wind direction. For a large attack angle like $20^{\circ}$, the instability characterizes a two-degree-of-freedom (2-DOF) oscillation with elliptical trajectories. For an attack angle of $15^{\circ}$, the instability can transform from the 1-DOF pattern to the 2-DOF one with the increase of the Reynolds number. Furthermore, the two instabilities show different sensitivity to the structural damping. The 1-DOF instability can be either completely suppressed or reduced to an unsteady oscillation, while the 2-DOF one is relatively less sensitive to the damping level. Reynolds number has important effects on the wake-induced instabilities.

• Wind and Structures
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• 제22권2호
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• pp.161-184
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• 2016

Long-span suspension bridges have evolved through the years and with them, the bridge girder decks improved as well, changing their shapes from standard box-deck girders to twin box and multi-box decks sections. The aerodynamic characteristics of the new generation of twin and multiple-decks are investigated nowadays, to provide the best design wind speeds and the optimum dimensions such bridges could achieve. The multi-box Megane bridge deck is one of the new generation bridge decks, consisting of two side decks for traffic lanes and two middle decks for railways, linked between them with connecting beams. Three-dimensional CFD simulations were performed by employing the Large Eddy Simulation (LES) algorithm with a standard Smagorinsky subgrid-scale model, for $Re=9.3{\times}10^7$ and angles of attack ${\alpha}=-4^{\circ}$, $-2^{\circ}$, $0^{\circ}$, $2^{\circ}$ and $4^{\circ}$. Also, a wind tunnel experiment was performed for a scaled model, 1:80 of the Megane bridge deck section, for $Re=5.1{\times}10^5$ and the aerodynamic static coefficients were found to be in good agreement with the results obtained from the CFD-LES model. However the aerodynamic coefficients determined individually, from the CFD-LES model, for each of the traffic and railway decks of the Megane bridge, varied significantly, especially for the downstream traffic deck. Also the pressure distribution and the effect of the spacing between the connecting beams, on the wind speed profiles showed a slight increase in turbulence above the downstream traffic and railway decks.

• 터널과지하공간
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• 제28권3호
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• pp.232-246
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• 2018

이 연구에서는 탄성파 속도를 이용한 암반분류(RMR)의 근거를 정량적으로 확인하기 위해 3공의 시추공 시추자료(지층 경계, RMR 등)와 현장 탄성파 측정 자료들과의 관계를 살펴보았다. 현장에서 획득된 탄성파 속도는 심도가 증가함에 따라 단조증가의 경향을 보인다. 각 시추공의 동일 심도에서 RMR, RQD, 절리간격 등의 상호상관성이 관찰되었으나, 탄성파 속도(Vp)는 RQD, 절리간격, UCS, 암편 Vp, RMR 등과 상관관계가 없는 것으로 나타났다. 반면, 시추공(3공)에서 모든 자료에 대하여 심도를 고려하지 않고 분석하였을 경우 현장 탄성파 속도와 대부분의 RMR 인자들은 상관성이 낮지만(예: 일축압축강도와 절리간격의 결정계수: 각각 0.039와 0.091), RMR과 RQD는 상대적으로 높은 상관관계가 있는 것으로 나타났다(RQD와 RMR의 결정계수: 각각 0.193과 0.211). 이러한 결과는 현장 탄성파 속도로부터 각 심도 지점에서의 개별 인자 값의 유추는 불가능하지만, 암반의 전반적인 물성을 포함하고 있는 RMR의 상관관계를 이용하여 개략적인 지반특성의 파악은 가능하다는 점을 시사한다. 아울러, 널리 이용되는 품셈의 연암-보통암의 경계값이 시추조사를 통해 실제 지반의 연암-보통암 경계값에 비해 속도가 느림이 관찰되는데, 이는 품셈의 기준을 재정립할 필요가 있음을 지시한다.

• 터널과지하공간
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• 제22권6호
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• pp.403-411
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• 2012

최근 국내에서는 폐광산 지반보강공사를 실시함에 있어 수압식 충전법을 적용하는 사례가 증가하고 있으나 효율적인 충전법 적용을 위해 현장 특성을 고려한 다양한 연구가 미흡한 실정이다. 본 연구에서는 수압식 충전공법의 충전효율 개선을 위한 선단장치 개발을 위하여 수조 모형실험 및 현장실험을 실시하였다. 수조 모형 실험을 통해 동일조건 하에서 선단장치 노즐각도 및 노즐형태 변화에 따른 충전효율을 평가하고, 이로부터 고안된 선단장치 모델을 현장실험에 적용한 결과, 노즐각 $90^{\circ}$관을 사용한 경우 일반적인 수직관을 사용한 경우에 비해 충전량이 약 18% 증가하는 것을 확인할 수 있었다. 이때 안식각은 $30.82^{\circ}$였다. 현장에서는 일반적으로 안식각을 $40^{\circ}$로 가정하고 충전공 간격을 5m에서 최대 10m 이내로 설계하였지만, 본 연구 결과에 따라 안식각을 $30^{\circ}{\sim}35^{\circ}$로 적용하면 충전공 간격을 최소 10m에서 최대 15m까지 넓히는 것이 가능하여 경제적이고 효율적인 채굴적 충전이 가능할 것으로 기대된다.