• 한국터널지하공간학회 논문집
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• 제19권2호
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• pp.231-248
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• 2017

서울시는 도심지 교통체증을 해결하기 위해 최근 경부고속도로의 일부 구간을 복층터널로 계획하는 방안을 검토하고 있다. 도심지에 복층터널을 건설할 경우, 교통난 해소뿐만 아니라 말레이시아 스마트 터널과 같이 홍수 시 침수방지를 위한 저류시설로도 활용할 수 있을 것으로 본다. 그러나 도로터널을 복층터널로 계획할 경우에는 각 지역을 연결하는 분기터널이 필요하며, 분기터널은 토피가 낮은 구간에 편평율이 큰 대단면 또는 복잡한 터널 단면형상으로 이루어지게 된다. 이때 토피가 낮은 지역에서는 지하 공동구나 건물 기초 등에 인접하여 위치하게 되며 터널 건설로 인해 지장물에 미치는 영향에 대해 반드시 검토해야 한다. 본 연구에서는 복층터널에서 분기되는 터널 굴착 시, 지하 공동구에 미치는 영향을 수치해석을 통해 분석하였다. 변위조절모델(Displacement Controlled Model)을 이용하여 터널 주변의 지반손실률을 1.0%, 3.0%, 그리고 5.0%까지 모사하였다. 복층터널에서 분기되는 각도를 $45^{\circ}$와 $36^{\circ}$로 다르게 설정하여 공동구 측면 및 하부로의 접근을 고려할 수 있도록 하였다. 그 결과, 일반적으로 분기터널이 공동구에 근접할수록 그리고 지반손실률이 클수록 변위, 각변위 그리고 안정성에 미치는 영향이 큰 것으로 타나났다. 공동구 바닥부의 침하와 공동구 부재의 안정성에는 이격거리 보다는 공동구의 하부에 근접하여 큰 변위와 부등침하를 유발할 수 있는 각도 $36^{\circ}$, 이격거리 10 m가 가장 취약한 것으로 나타났다. 본 연구를 통해 근접시공 시 구조물의 안정성 평가를 위한 각변위-거리/직경 관계를 제시하였으며, 지하 공동구 안정성에 영향을 미치는 한계 임계 지반손실률을 산정하였다.

• Geomechanics and Engineering
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• 제21권2호
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• pp.111-122
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• 2020

In most cases in urban areas, construction of divergence tunnel should take into account proximity to existing tunnel in operation. This inevitably leads to deformation of adjacent structures and surrounding ground. Preceding researches mainly dealt with reinforcing of the diverging section for the stability including the pillar. This has limitations in investigating the interactive effects between existing structures and surrounding ground due to the excavation of the divergence tunnel. In this study, the complex interactive behavior of pile, the operating tunnel, and the surrounding ground according to horizontal offsets between the two adjacent tunnels was quantitatively analyzed based on conditions diverged from operating tunnel in urban areas. The effects on ground structures confirmed by analyzing the ground surface settlements, pile settlements, and the axial forces of the pile. The axial forces of lining in operating tunnel investigated to estimate their impact on existing tunnel. In addition, in order to identify the deformation of the surrounding ground, the close range photogrammetry applied to the laboratory model test for confirming the underground displacements. Two-dimensional finite element numerical analysis was also performed and compared with the results. It identified that the impact of excavating a divergence tunnel decreased as the horizontal offset increased. In particular, when the horizontal offset was larger than 1.0D (D is the diameter of operating tunnel), the impact on existing structures further reduced and the deformation of surrounding ground was concentrated at the top of the divergence tunnel.

• 한국터널지하공간학회 논문집
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• 제19권5호
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• pp.779-797
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• 2017

최근 도심지의 지상교통시설이 포화수준에 이르렀을 뿐만 아니라 증가하는 교통량으로 인한 교통난과 미세먼지 등의 대기환경 오염의 심화로 인하여 지하도로건설이 각광을 받고 있다. 지하도로건설은 도심지 교통난 해소와 더불어 친환경적인 도시설계가 가능하기 때문에 신설도로 뿐만 아니라 기존도로 역시 지하화 되어 가는 추세이다. 지하도로건설시 IC(분기점)와 JC(나들목) 역할을 수행하는 분기터널의 건설은 필수적이라 할 수 있다. 따라서 분기터널에 의한 기존터널의 영향분석은 필수적으로 고려해야한다. 본 연구에서는 분기터널 굴착 시 기존터널에 미치는 영향을 수치해석을 통해 분석하였다. 분기터널을 기존터널의 직하부를 기점으로 하여 시계방향으로 $45^{\circ}$간격으로 총 5가지의 경우를 설정하였으며, 각각의 경우에서 변위조절방법(Displacement Controlled Model)을 이용하여 지반손실률을 0.5%, 1.0% 그리고 1.5%을 적용하여 수치해석을 실시하였다. 그 결과, 지반손실률이 증가할수록 변위와 파괴범위, 그리고 안정성에 미치는 영향이 증가하는 것으로 나타났다. 또한 직하부에 위치한 분기터널이 가장 안정성에 취약한 것으로 확인 되었으며, 분기터널의 위치가 연직, 수평방향에 있을 경우보다 대각선방향에 위치할 경우가 변형과 라이닝 파괴 측면에서 불안정한 것으로 나타났다.

• 한국터널지하공간학회 논문집
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• 제22권4호
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• pp.435-450
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• 2020

복층터널의 분기구간은 터널 형상이 모자 모양의 대단면 구간인 '분기 전 확폭구간'과 본선과 분기터널 간 이격이 생기는 '분기 후 구간'으로 나눌 수 있으며, 분기 전 확폭구간의 터널 단면이 분기 후 구간의 단면에 비해 매우 크기 때문에 이러한 차이에 따른 굴착 영향이 분기구의 전체적인 굴착 안정성 검토 시 고려되어야 한다. 본 연구에서는 암반에서 시공되는 NATM 방식의 2차로 대심도(40 m) 본선 복층터널에서 1차로 단층터널로 분기가 되는 조건을 대상으로 3차원 유한요소해석을 통해 분기 전 확폭구간 굴착(선행굴착) 시 굴착공법과 벤치길이 변화에 따라 선행굴착이 분기 후 구간의 굴착 안정성에 미치는 영향을 검토하였다. 그 결과, 굴착공법과 벤치길이 변화에 따른 차이는 상대적으로 작은 편이었으나, 2차원 수치해석에 의한 선행굴착을 고려하지 않은 경우와 강도응력비 비교를 통해 선행굴착이 분기 후 구간의 굴착 안정성에 영향을 미칠 정도로 큰 응력의 변화를 유발함을 확인하였다.

• 한국지반신소재학회논문집
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• 제15권2호
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• pp.45-54
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• 2016

본 연구에서는 증가하는 도심지 정체와 신설터널 건설에 따른 여러 제약의 문제를 해소하는 방안으로 향후 국내에서 수요가 증가할 것으로 전망되는 대심도 지하도로를 복층터널로 건설시 본선 복층터널에서 단층터널로 분기가 되는 구간의 터널 거동과 본선과 분기터널간의 필라 안정성을 수치해석을 통하여 검토하였다. 이를 위해 본선터널과 분기터널의 이격거리를 본선터널의 직경(D)을 기준으로 0.1D부터 2.0D까지 변화하는 조건과 지반조건을 암반등급에 따라 1~5등급으로 변화하는 조건들에 대하여 유한요소해석을 수행하였으며, 터널의 전체적인 거동과 함께 그 결과를 기반으로 기존의 경험식 등을 이용한 안전율, 강도-응력비, 그리고 간섭체적비를 산정하여 굴착에 따른 안정성 영향을 검토하였다. 검토 결과 수치해석결과를 이용해 산정된 강도-응력비와 간섭체적비는 경험식을 이용한 방법에 비해 암반강도보다는 이격거리가 안정성에 더욱 크게 영향을 미침을 나타내었고, 그에 따라 본선과 분기터널의 이격거리가 0.7D 이하인 경우는 본선과 분기터널을 모자 형태의 하나의 대단면으로 시공하는 것이 안정성 측면에서 유리한 것으로 판단되었다.

• Geomechanics and Engineering
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• 제21권2호
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• pp.95-102
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• 2020

Population concentration in urban areas has led traffic management a central issue. To mitigate traffic congestions, the government has planned to construct large-cross-section tunnels deep underground. This study focuses on estimating the damage caused to frame structures owing to tunnel excavation. When constructing a tunnel network deep underground, it is necessary to divide the main tunnel and connect the divergence tunnel to the ground surface. Ground settlement is caused by excavation of the adjacent divergence tunnel. Therefore, predicting ground settlement using diverse variables is necessary before performing damage estimation. We used the volume loss and cover-tunnel diameter ratio as the variables in this study. Applying the ground settlement values to the settlement induction device, we measured the extent of damage to frame structures due to displacement at specific points. The vertical and horizontal displacements that occur at these points were measured using preattached LVDT (Linear variable differential transformer), and the lateral strain and angular distortion were calculated using these displacements. The lateral strain and angular distortion are key parameters for structural damage estimation. A damage assessment chart comprises the "Negligible", "Very Slight Damage", "Slight Damage", "Moderate to Severe Damage", and "Severe to Very Severe Damage" categories was developed. This table was applied to steel frame and concrete frame structures for comparison.

• Wind and Structures
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• 제30권3호
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• pp.317-323
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• 2020

A novel approach is presented to improve dynamic responses of a pedestrian bridge by utilizing decorative wind chimes. Through wind tunnel tests, it was verified that wind chimes can provide stabilization effects against flutter instability, especially at positive or negative wind angles of attack. At zero degrees of angle of attack, the wind chimes can change the flutter pattern from rapid divergence to gradual divergence. The decorative wind chimes can also provide damping effects to suppress the lateral sway motion of the bridge caused by pedestrian footfalls and wind forces. For this purpose, the swing frequency of the wind chimes should be about the same as the structural frequency, which can be achieved by adjusting the swing length of the wind chimes. The mass and the swing damping level are other two important and mutually interactive parameters in addition to the swing length. In general, 3% to 5% swing damping is necessary to achieve favorite results. In the study case, the equivalent damping level of the entire system can be increased from originally assumed 1% up to 5% by using optimized wind chimes.

• Wind and Structures
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• 제37권1호
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• pp.57-78
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• 2023

In this study, a generalized three-degree-of-freedom (3-DoF) analytical model is formulated to predict linear aerodynamic instabilities of a prism under quasi-steady (QS) conditions. The prism is assumed to possess a generic cross-section exposed to turbulent wind flow. The 3-DoFs encompass two orthogonal horizontal directions and rotation about the prism body axis. Inertial coupling is considered to account for the non-coincidence of the mass center and the rotation center. The aerodynamic force coefficients-drag, lift, and moment-depend on the Reynolds number based on relative flow velocity, angle of attack, and the angle between the wind and the cable. Aerodynamic forces are linearized with respect to the static equilibrium configuration and mean wind velocity. Routh-Hurwitz and Liénard and Chipart criteria are used in the eigenvalue problem, yielding an analytical solution for instabilities in galloping and static divergence types. Additionally, the minimum structural damping and stiffness required to prevent these instabilities are numerically determined. The proposed 3-DoF instability model is subsequently applied to a conductor with ice accretion and a full-scale dry inclined cable. In comparison to existing models, the developed model demonstrates superior prediction accuracy for unstable regions compared with results in wind tunnel tests.

• Wind and Structures
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• 제28권4호
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• pp.255-270
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• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• Geomechanics and Engineering
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• 제15권3호
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• pp.869-877
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• 2018

The continually growing demand for underground space in dense urban cities is also driving the demand for underground highways. Building the underground highway tunnel, however, can involve complex design and construction considerations, particularly when there exists divergence or convergence in the tunnel. In this study, interaction between two asymmetric noncircular tunnels-that is, a larger main tunnel and a smaller tunnel diverging from the main tunnel, was investigated by examining the distributions of the principal stresses and the strength/stress ratio for varying geometric conditions between the two tunnels depending on diverging conditions using both numerical analysis and scale model test. The results of numerical analysis indicated that for the $0^{\circ}$, $30^{\circ}$, $60^{\circ}$ diverging directions, the major principal stress showed an initial gradual decrease and then a little steeper increase with the increased distance from the left main tunnel, except for $90^{\circ}$ where a continuous drop occurred, whereas the minor principal stress exhibited an opposite trend with the major principal stresses. The strength/stress ratio showed generally a bell-shaped but little skewed to left distribution over the distance increased from the left larger tunnel, similarly to the variation of the minor principal stress. For the inter-tunnel distance less than 0.5D, the lowest strength/stress ratio values were shown to be below 1.0 for all diverging directions ($0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$). The failure patterns observed from the model test were found to be reasonably consistent with the results of numerical analysis.