• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.287-301
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• 2009

The novel cut-and-cover tunnel construction method using rib-reinforced pre-cast arch segments has been recently developed and applied for practice to secure a structural stability of high covering and wide width section tunnels. Cut-and-cover tunnels are usually damaged by the seismic behavior of backfill grounds in case of a low covering condition. Seismic analyses are performed in this study to characterize the dynamic behavior of rib-reinforced pre-cast arch cut-and-cover tunnels. Seismic analyzes for 2 lane cast-in-place and rib-reinforced pre-cast arch cut-and-cover tunnels are carried out by using the commercial FDM program (FLAC2D) considering various field conditions such as the covering height embankment slope and excavation slope. It can be concluded that the amplification of seismic wave is reduced due to an increase in the structural stiffness induced by rib-reinforcement. The results show that the rib-reinforced pre-cast arch cut-and-cover tunnels are more effective against the seismic loading, compared to the cast-in-place cut-and-cover tunnels.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.17-28
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• 2002

Tunnel construction is a complex three dimensional operation. Since, however, it is neither possible nor useful to simulate all conditions and parameters in detail, a simplified two dimensional model is commonly employed in practice. The simulation of three dimensional conditions by a two dimensional model should use empirical parameters. The numerical predictions indicate that analysis results are highly dependent on the parameters. An improved modelling method based on time was adopted to account for three dimensional effect at the tunnel heading and time dependent nature, and used to perform an analysis of tunnelling in decomposed granite. The effects of weathering degree, tunnel shape and multi-drift excavation were investigated by using the method. It is identified that a structural benefit can be obtained by adopting a horse-shoe-shaped cross section with multi-drift excavation in mixed-force ground condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.59-70
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• 2008

도심지 터널의 설계, 시공 그리고 유지관리에 있어서 지반 변위 억제와 변형거동 예측은 중요하다. 국내 외 연구자들은 다양한 수치해석적인 기법과 현장 계측 결과를 이용하여 터널 시공과 관련된 변형거동 예측을 시도하였다. 하지만, 설계물성치의 산정과 지반 모델링 그리고 수치해석기법과 관련된 사용상의 어려움에 의해 아직까지 만족스러운 결과를 얻지는 못하였다. 본 논문은 수치해석적인 기법과 인공신경망을 이용하여 도심지 NATM 터널의 설계 물성치 산정과 변형거동 예측에 관한 방법을 제안하였다. 인공신경망 모델 개발을 위한 학습과 테스트과정은 데이터베이스된 수치해석결과를 이용하였다. 개발된 인공신경망 모델은 입력변수인 지반변위와 결과변수인 설계 물성치 간의 상호관계를 적절히 인식할 수 있다. 수치해석은 지반의 연화거동을 모사할 수 있는 변형률 연화모델을 적용하였다. 사례분석에 있어서 굴착 초기단계의 계측 값을 개발된 인공신경망 모델에 입력하여 설계 물성치를 계산하였으며, 수정된 설계 물성치는 수치해석을 통하여 다음 굴착단계에서의 터널 주변의 지반 변형거동을 예측하였다. 본 논문에서 제안된 방법을 토대로 시공조건이 엄밀한 도심지 터널의 설계물성치의 정량적인 평가 및 변형거동 예측이 계측이 입수된 초기 굴착단계에서 가능할 것으로 기대된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.77-89
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel that allows tunnel segments to float underwater by buoyancy, and is being actively studied in recent years. When the submerged floating tunnel is connected to the ground, the tunnel and the bored tunnel inside the ground must be connected. There is risk that the stress will be concentrated at the connection between the two tunnels due to the different constraints and behavior of the two tunnels. Therefore, special design and construction methods should be applied to ensure the stability around the connection. However, previous studies on the stability at the connection site have not been sufficiently carried out, so study on the basic stage of the stability at connection site are necessary. In this study, numerical analysis simulating the connection between submerged floating tunnel and the bored tunnel confirmed that the shear strain concentration occurred in the ground around the connection, and it was analyzed that the structural factors can be handled during construction to have effects on the stability of the ground around the connection. Numerical results show that the risks from disproportionate displacements in the two tunnels can be mitigated through the construction of grouting material and joint design. Although the results from this study are qualitative results, it is expected that it will contribute to the determination of structural factors and risk areas that should be considered in the design of connections between the submerged floating tunnel and bored tunnel in the future studies.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.98-106
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• 2008

When a tunnel is excavated in a rock mass of poor condition, the adjacent zone of excavation surface may be reinforced by adopting the appropriate methods such as grouting and rock bolting. The reinforced effect can be evaluated by use of various numerical approaches, where the reinforcing elements may be expressed as distinct discretizations or smeared into the equivalent material properties. In this study, a simple numerical method, which can be classified as the latter approach, was developed for the elasto-plastic analysis of a circular tunnel. If a circular tunnel in a Mohr-Coulomb rock mass is reinforced to a finite thickness, the reinforced annulus may have different material properties from the in-situ rock mass. In the proposed elasto-plastic method for assessing the reinforcing effect, Lee & Pietruszczak (2007)'s method is applied to both the reinforced annulus and the outer insitu rock mass of the fictitious tunnel, and then two results are combined by enforcing the compatibility condition. The method were verified through comparing the results with the proposed method and the commercial finite difference code FLAC. When taking the variation of deformation modulus and strength parameters in the reinforced zone into account, the distributions of stress and radial displacement were much different from those obtained with the assumption of homogeneous rock mass.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.115-134
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• 2003

Recently, there are many cases in the roadway design for successive tunnel with small distance between two tunnels. In this case, the degree of interference for successive tunnels is a significant consideration in the design of ventilation systems. Also, Re-inflows of contaminated air in successive tunnel make serious ventilation problems in case of fire accident in the tunnel. In this study, for successive tunnels in Donghae highway project, the concentration of contaminant such as CO, NOx and Smoke were calculated by numerical analysis using 1D and 3D-CFD analysis. And, the rate of re-inflow at the portals of successive tunnel according to the direction of wind were analysed.

• The Journal of Engineering Geology
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• v.6 no.3
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• pp.111-118
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• 1996

In general, a three dimensional ground behaviour during tunneling is simulated by using two dimensional analysis programs in consideration of a certain ratio of stress or strain distribution to take into account the effect of construction stage by a tunnel face advance. A series of trree dimensional analyses was conducted to deduce a normalized displacement (surface or crown settlement) curve in longitudinal direction, of which curve is reflecting an effect of a tunnel advance under a various condition. And, by using try and error technique, two dimensional analyses were carried out to determine an optimum stress distribution ratio for a settiement curve coincided with the curve obtained by three dimensional analyses. Finally, monitored results from a subway tunnel were compared with two dimensional analysis results for varification of the deduced stress distribution ratio as well as the two dimensional analysis program employed in this study.

• Computational Structural Engineering
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• v.11 no.3
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• pp.187-198
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• 1998

지하구조물의 건전성을 평가하기 위한 비파괴시험으로써 탄성응력파를 이용한 충격반향탐사법을 수치해석적인 방법을 통하여 수행하였다. 즉, 일면만으로 접근 가능한 터널 면에서의 충격가진과 동적응답의 측정으로 이질면을 포함한 내부의 상태를 예측할 수 있다. 연구의 수행은 탄성거동을 하는 매질 내부에서 전파되는 탄성응력파의 특성을 이해하고, 이를 동적 유한요소해석으로 모형화하여 충격반향탐사법을 수치해석적으로 수행한다. 이질재료가 2개의 층을 이루고 있는 경우 표면층의 두께를 쉽게 측정할 수 있었으며, 구조물의 병진운동, 휨운동과 구조물 내에서 다중반사되는 탄성응력파에 의한 복합적인 영향을 받는 터널과 같은 원통형 구조물에서 동적응답의 주파수 특성으로부터 터널라이닝 내부에 형성된 공동의 위치와 크기의 예측이 가능하였다. 수치해석적인 방법과 병행하여 다양한 형태의 경계조건을 가지는 구조물에 대한 충격반향탐사법의 실험을 수행할 경우 실제적인 문제에 적용, 건전성 평가의 지표를 마련할 수 있을 것으로 사료된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.1
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• pp.71-83
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• 2004

The purpose of this study is to present an analysis method for the prediction of the changes m ground conditions. To this end, three dimensional convergence displacements are analyzed in several ways to estimate the trend of displacement changes. Three-dimensional arching effect is occurred around the unsupported excavation surface including tunnel face when a tunnel is excavated in a stable rock mass. If the ground condition ahead of tunnel face changes or a weak zone exists, a diagnostic trend of displacement change is observed by the 3 dimensional measurement and numerical analysis. Therefore, the change of ground condition and the existence of a weak zone ahead of tunnel face can be predicted by monitoring 3-dimensional absolute displacements during excavation, and applying the methodology (the ratio of L/C, $C/C_o$, etc.) presented in this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.159-181
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• 2012

The segment lining which consists of segments and joints are main component of shield tunnel. There are a number of methods that are being used in design which compute the sectional forces of a ring of segment lining. The traditional design methods which do not consider the effect of joints have been commonly used for design procedure without a specific verification of structural analysis. This paper presents the result of a comparative study for analytical and numerical models of the shield tunnel segment lining. For the traditional methods, the elastic equation method and the Duddeck & Erdmann method were considered. The ring-beam and the continuum analysis model were also considered as the numerical model.