• Magazine of korean Tunnelling and Underground Space Association
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• v.2 no.1
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• pp.130-138
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• 2000

본 연구에서는 수평보강재로 보강된 터널 막장의 거동에 관한 매개변수 연구결과를 다루었다. 매개변수 연구에서는 막장주변의 3차원 응력-변형율 거동을 보다 효율적으로 모델링하기 위해 3차원 유한요소해석 모형을 적용하였으며 보강패턴에 따른 막장의 거동을 고찰하기 위해 다양한 경계조건에 대한 해석을 수행하였다. 해석결과를 토대로 막장의 응력해방-변위거동의 관계를 고찰하였으며, 보강패턴과 막장 변위의 정성${\cdot}$정량적인 관계를 제시함과 아울러서 향후 수행될 반경험적 설계/해석법의 개발을 위한 데이터베이스를 구축하였다. 한편, 해석결과 보강재 타설수 및 길이 등 각 보강설계 인자에 대한 임계치가 존재하는 것으로 나타났으며 따라서 보다 안전하고 경제적인 설계를 위해서는 이를 고려하여야 할 것으로 판단된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.4
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• pp.323-336
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• 2003

Recently, the development of tunnel reinforcement method has been required relating to the shallow tunnelling in soft ground. In this study, the improvement method on tunnel stability is proposed by evaluating the efficiency of face reinforcement which enables to control extrusion of advance core, however, it is often neglected in urban tunnelling under the poor ground conditions. Systematic pre-confinement ahead of the face improves the tunnel stability, subsequently, displacement of the crown and surface settlement can be restrained by proper method. 3-dimensional numerical analysis including horizontal reinforcement modelling on a face is applied to estimate the behaviour of a tunnel in relation to the ground and reinforcement conditions. Consequently, extrusion at the face decreases significantly after using the horizontal reinforcement and the effect of reinforcement is much increased in case of applying the supplemental reinforcement ahead of the face together. Especially, confinement effect around the tunnel and the core is proved by means of the core reinforcement in poor ground conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.91-100
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• 2002

This paper presents the results of laboratory investigation on the deformation behavior of tunnel face reinforced with longitudinal pipes. A series of reduced-scale model tests was carried out to investigate the effect of reinforcement layout on the tunnel face axial displacement as well as the surface settlement. Among other things, the results of the model tests indicate that the axial displacement of tunnel face as well as the ground surface settlement can significantly be reduced by pre-reinforcing the tunnel face with longitudinal pipes, suggesting that the pre-reinforcing technique may effectively be used as a positive ground control method in the urban environments. Also illustrated is that the reinforcing effect is significantly influenced by the reinforcement layout. The implications of the findings from this study are discussed in a great detail.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.32-40
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• 2000

This paper presents the results of a parametric study on the behavior of tunnel face reinforced with horizontal pipes. A series of reduced-scale model tests was carried out to in an attempt to verify previously performed three-dimensional numerical modeling and to investigate effects of reinforcement layout on the tunnel face deformation behavior. The results of model tests indicate that the tunnel face deformation can significantly reduced by pre-reinforcing the tunnel face with longitudinal members and thus enhancing the tunnel stability. In addition, the model tests results compare fairly well with those from the previously performed three-dimensional finite element analysis. Therefore, a properly calibrated three dimensional model may effectively be used in the study of tunnel face reinforcing technique.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.5
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• pp.359-368
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• 2010

Unlike in Korea where steel pipe-reinforced multistep grouting is of commonly used methods for tunnel reinforcement, face bolt method is more widely used due to its better workability and lower construction cost in other countries. In this paper, the effects of both methods after tunnel failure were numerically analyzed and verified based on the oversea construction experiences. As a result it is concluded that the face bolt method may be effective to reinforcement especially when there are some fractured zones developed in the face of tunnel.

• Journal of the Korean Geotechnical Society
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• v.22 no.6
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• pp.71-82
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• 2006

One of the most popular pre-reinforcement methods of tunnel heading in cohesionless soils would be the fore-polling of grouted pipes, known as RPUM (reinforced protective umbrella method) or UAM (umbrella arch method). This technique allows safe excavation even in poor ground conditions by creating longitudinal arch parallel to the tunnel axis as the tunnel advances. Some previous studies on the reinforcing effects have been performed using numerical methods and/or laboratory-based small scale model tests. The complexity of boundary conditions imposes difficulties in representing the tunnelling procedure in laboratory tests and theoretical approaches. Full-scale study to identify reinforcing effects of the tunnel heading has rarely been carried out so far. In this study, a large scale model testing for a tunnel in granular soils was performed. Reinforcing patterns considered are four cases, Non-Reinforced, Crown-Reinforced, Crown & Face-Reinforced, and Face-Reinforced. The behavior of ground and pipes as reinforcing member were fully measured as the surcharge pressure applied. The influences of reinforcing pattern, pipe length, and face reinforcement were investigated in terms of stress and displacement. It is revealed that only the Face-Reinforced has decreased sufficiently both vertical settlement in tunnel heading and horizontal displacement on the face. Vertical stresses along the tunnel axis were concentrated in tunnel heading from the test results, so the heading should be reinforced before tunnel advancing. Most of maximum axial forces and bending moments for Crown-reinforced were measured at 0.75D from the face. Also it should be recommended that the minimum length of the pipe is more than l.0D for crown reinforcement.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.536-549
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• 2005

국내 대부분을 차지하고 있는 NATM의 주요원리는 주변지반의 지보효과를 활용하는 터널굴착공법이다. 따라서 실제 지반조건이 원설계조건 보다 역학적으로 불량한 경우 보강공법의 적용은 필수적이라 할 수 있으나, 합리적인 설계변경은 현실적으로 쉽지 않은 실정이다. 또한 현실적인 이유로 양방향으로 터널을 관통하는 설계법과 달리 종종 1방향 굴진으로 터널을 관통하는 경우가 있다. 그러나 이러한 1방향 굴진은 불가분 굴진 종점부에서 저토피 갱구를 향하게 되므로, 지반이 연약한 경ㅇ우 막장 붕괴의 위험이 매우 높은 것으로 알려져 있다. 본 터널은 설계 시 갱구부 지반을 풍화암과 연암으로 보고 설계 하였으나, 실제 굴착 시 확인된 지층은 핵석을 포함한 실트질모래(SP-SM)로 판명되었다. 더구나 터널굴진 방향에 있어서도 양방향 굴착이 아닌 저토피 갱구를 향한 1방향 굴진을 실시하였으며, 이러한 시공 중에 터널관통을 불과 19m 남겨둔 갱구부에서 막장부괴와 동시에 상부사면 함몰이 발생하였다. 본 연구는 토사터널 갱구부 1방향 굴진 시 발생한 막장붕괴 보강사례로서, 지상보강(시멘트밀크 그라우팅)과 갱내보강(방사상 FRP보강그라우팅) 그리고 인버트폐합을 실시하여 성공적으로 터널시공을 완료한 사례연구이다. 본 사례는 향후 토사터널 갱구부의 설계와 시공에 유용한 참고자료가 될 것이다.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.328-338
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• 2001

Horizontal tunnel face reinforcement using Fiber Glass Tube(FGT) or steel pipe and pipe roofing techniques are frequently used when the stability of newly excavated tunnel is not guaranteed. However, the mechanical behavior of tunnels using these techniques has not been fully understood so far. Therefore, engineering rule of thumb is commonly applied during designing procedure, and it is difficult to adopt these techniques rationally. In this study, the application of a simplified numerical analysis method based on composite mechanics is verified. The mean field theory and the strain energy theory are used to obtain the equivalence elastic moduli of reinforced soil and rock. Furthermore, a parametric study on the deformational behavior of tunnel face is performed for various patterns of prereinforcement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.11-22
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• 2009

Tunnel excavation with several sections and appropriate auxiliary measures such as face bolt and pre-grouting are widely used in case of weak and less rigid ground for the stability of a tunnel face during excavation. This papers first described the evaluation methods proposed in technical literature to maintain the tunnel face stable, and then studied by FEM analysis whether face reinforcement is need in what degree of ground deformation and strength features for the stability of a tunnel face when excavating by full excavation with sub-bench. Lastly, a three dimensional FEM analysis was performed to study how the tunnel face itself and the ground around the tunnel behave depending on different bolt layouts, length of bolts, number of bolts. There were relative differences in comparison of results on the stability of a tunnel face by a theoretical evaluation methods and FEM analysis, but the same in reinforced effect of face. It was found that the stability of a tunnel face can be obtained with face bolt installed longer than 1.0D (tunnel width), bolt density of about 1 bolt per every $1.5\;m^2$ (layout of grid type), and reinforcement area of $120^{\circ}$ arch area of upper section.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.3
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• pp.185-193
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• 2002

In this paper, deformation behavior of shallow subway tunnel excavated in weathered soil and reinforcement effects of longitudinal support measures are investigated via three dimensional FDM analysis. Two excavation methods, half-face excavation and full-face excavation, are considered in simulation to study the influences of excavation methods on tunnel deformation behavior. In addition, the reinforcing effects of RPUM and fiberglass pipe are compared. Face extrusion, covergence, preconvergence, and sidewall displacement are investigated to analyze tunnel deformation behavior, and surface settlement is used to analyze the effects of excavation methods and longitudinal supports measures. The simulation results show that half-face excavation induces larger convergence, preconvergence, sidewall displacement, surface settlement than full-face excavation, while full-face excavation induces larger extrusion than half-face excavation. In addition, under same excavation method, all displacements are larger when RPUM is only used for longitudinal support than when RPUM is jointly used with fiberglass pipes.