• Title/Summary/Keyword: tunnel face

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Prediction of Fault Zone ahead of Tunnel Face Using Longitudinal Displacement Measured on Tunnel Face (터널 굴진면 수평변위를 이용한 굴진면 전방의 단층대 예측)

  • Song, Gyu-Jin;Yun, Hyun-Seok;Seo, Yong-Seok
    • The Journal of Engineering Geology
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    • v.26 no.2
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    • pp.187-196
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    • 2016
  • We conducted three-dimensional finite element analysis to predict the presence of upcoming fault zones during tunneling. The analysis considered longitudinal displacements measured at tunnel face, and used 28 numerical models with various fault attitudes. The x-MR (moving range) control chart was used to analyze quantitatively the effects of faults distributed ahead of the tunnel face, given the occurrence of a longitudinal displacement. The numerical models with fault were classified as fault gouge, fault breccia, and fault damage zones. The width of fault cores was set to 1 m (fault gouge 0.5 m and fault breccia 0.5 m) and the width of fault damage zones was set to 2 m. The results, suggest that fault centers could be predicted at 2~26 m ahead of the tunnel face and that faults could be predicted earliest in the 45° dip model. In addition, faults could be predicted earliest when the angle between the direction of tunnel advance and the strike of the fault was smallest.

Seismic reflection imaging ahead of tunnel face using 3 component geophones (3성분 지오폰을 이용한 막장전방 예측 탄성파탐사)

  • Jo Churl Hyun;Cha Young Ho;Yang Jong Hwa;Bang Ki Moon
    • Proceedings of the KSR Conference
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    • 2005.11a
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    • pp.412-417
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    • 2005
  • To ensure the safety of the tunnelling without the loss of economy, the tunnel seismic profiling(TSP) method for the prediction ahead of tunnel face, begins to be used routinely in these days. TSP method does not interfere the tunnelling works while the horizontal drilling does, and its prediction length is longer than that of the drilling. Yet the most frequently adopted technique of TSP in Korea is the multi-shot and 2 receiver array using in-hole receivers, even though this array requires as many as 26 drill-holes for receiver installation and ballasting, which results in 3-6 hours of suspension in excavation work. In this paper, multi-receiver and lesser shot array using side-wall attached 3 component geophones is to be described to prove the efficiency in terms of the survey time as well as the reliability of the method by comparison of the predicted weak points and the face mapping results. The predictions mostly agreed with the real fractures or joint developed zones which have been confirmed during the excavation. It also has been found that TSP method can be effectively applied to perform draining ground water ahead of tunnel face by imaging the geologic discontinuities.

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Characterization of face stability of shield tunnel excavated in sand-clay mixed ground through transparent soil models

  • YuanHai Li;XiaoJie Tang;Shuo Yang;YanFeng Ding
    • Geomechanics and Engineering
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    • v.33 no.5
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    • pp.439-451
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    • 2023
  • The construction of shield tunnelling in urban sites is facing serious risks from complex and changeable underground conditions. Construction problems in the sand-clay mixed ground have been more reported in recent decades for its poor control of soil loss in tunnel face, ground settlement and supporting pressure. Since the limitations of observation methods, the conventional physical modelling experiments normally simplify the tunnelling to a plane strain situation whose results are not reliable in mixed ground cases which exhibit more complicated responses. We propose a new method for the study of the mixed ground tunnel through which mixed lays are simulated with transparent soil surrogates exhibiting different mechanical properties. An experimental framework for the transparent soil modelling of the mixed ground tunnel was established incorporated with the self-developed digital image correlation system (PhotoInfor). To understand better the response of face stability, ground deformation, settlement and supporting phenomenon to tunnelling excavation in the sand-clay mixed ground, a series of case studies were carried out comparing the results from cases subjected to different buried depths and mixed phenomenon. The results indicate that the deformation mode, settlement and supporting phenomenon vary with the mixed phenomenon and buried depth. Moreover, a stratigraphic effect exists that the ground movement around mixed face reveals a notable difference.

Experimental verification for prediction method of anomaly ahead of tunnel face by using electrical resistivity tomography

  • Lee, Kang-Hyun;Park, Jin-Ho;Park, Jeongjun;Lee, In-Mo;Lee, Seok-Won
    • Geomechanics and Engineering
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    • v.20 no.6
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    • pp.475-484
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    • 2020
  • The prediction of the ground conditions ahead of a tunnel face is very important, especially for tunnel boring machine (TBM) tunneling, because encountering unexpected anomalies during tunnel excavation can cause a considerable loss of time and money. Several prediction techniques, such as BEAM, TSP, and GPR, have been suggested. However, these methods have various shortcomings, such as low accuracy and low resolution. Most studies on electrical resistivity tomography surveys have been conducted using numerical simulation programs, but laboratory experiments were just a few. Furthermore, most studies of scaled model tests on electrical resistivity tomography were conducted only on the ground surface, which is a different environment as compared to that of mechanized tunneling. This study performed a laboratory experimental test to extend and verify a prediction method proposed by Lee et al., which used electrical resistivity tomography to predict the ground conditions ahead of a tunnel face in TBM tunneling environments. The results showed that the modified dipole-dipole array is better than the other arrays in terms of predicting the location and shape of the anomalies ahead of the tunnel face. Having longer upper and lower borehole lengths led to better accuracy of the survey. However, the number and length of boreholes should be properly controlled according to the field environments in practice. Finally, a modified and verified technique to predict the ground conditions ahead of a tunnel face during TBM tunneling is proposed.

3D Tunnel Face Modelling for Discontinuities Characterization: A Comparison of Lidar and Photogrammetry Methods (불연속성 특성화를 위한 3차원 터널 막장 모델링: 라이더 및 사진 측량 접근 방식의 비교 분석 중심으로)

  • Chuyen, Pham;Hyu-Soung, Shin
    • Tunnel and Underground Space
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    • v.32 no.6
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    • pp.549-557
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    • 2022
  • Tunnel face mapping involves the determination of rock discontinuities or weak rock conditions where extra support might be required. In this study, we investigated the application of Lidar scanning and photogrammetry to quantitatively characterize discontinuities of the rock mass on the tunnel face during excavation. The 3D models of tunnel faces generated by using these methods enable accurate and automatic discontinuity measurement to overcome the limitations of manual mapping. The results of this study show that both photogrammetry and Lidar can be used to reconstruct the 3D model of the tunnel face, although the photogrammetric 3D model is less detailed than its counterpart produced by Lidar. Given acceptable accuracy and cost-effectiveness, photogrammetry can be a fast, reliable, and low-cost alternative to Lidar for acquiring 3D models and determining rock discontinuities on tunnel faces.

Reliability analysis of tunnel face stability considering seepage effects and strength conditions

  • Park, Jun Kyung
    • Geomechanics and Engineering
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    • v.29 no.3
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    • pp.331-338
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    • 2022
  • Face stability analyses provides the most probable failure mechanisms and the understanding about parameters that need to be considered for the evaluation of ground movements caused by tunneling. After the Upper Bound Method (UBM) solution which can consider the influence of seepage forces and depth-dependent effective cohesion is verified with the numerical experiments, the probabilistic model is proposed to calculate the unbiased limiting tunnel collapse pressure. A reliability analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and cohesive soil is presented to consider the inherent uncertainty in the input parameters and the proposed model. The probability of failure that exceeding a specified applied pressure at the tunnel face is estimated. Sensitivity and importance measures are computed to identify the key parameters and random variables in the model.

Stability Analysis of the Spillway Tunnel Located on the Granite Region Including Fault Fractured Zone (단층파쇄대를 포함한 화강암지역의 여수로 터널 안정성 분석)

  • Han, Kong-Chang;Ryu, Dong-Woo;Kim, Sun-Ki;Bae, Ki-Chung
    • Tunnel and Underground Space
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    • v.18 no.1
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    • pp.58-68
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    • 2008
  • The construction of an emergency spillway of Imha Dam is being in progress on the granite region including fault fractured zone. Considering that this tunnel is being excavated in three paralled rows, the pillar width between each tunnel and the face distance between each tunnel face were evaluated. The Influence of the fault fractured zone for the tunnel stability was investigated by numerical modelling in 3D. Various geophysical investigations and rock engineering field tests were carried out for these purposes. It was suitable that the second tunnel would be excavated in advance, maintaining the face distance between each tunnel face of minimum 25 m. The results of numerical modelling showed that the roof displacement and the convergence of the second tunnel were insignificant, and the maximum bending compressive stress, the maximum shear stress of shotcrete and the maximum axial force of rockbolt were also insignificant. Therefore, it was estimated that the stability of the spillway tunnel was ensured.

A study on the longitudinal optimum separated distance of tunnel face in 2-arch tunnel (2-Arch 터널의 막장면 종방향 적정 이격거리에 관한 연구)

  • Lee, Min-Kyu;Jeong, Ji-Su;Lee, Sung-Ki;Lee, Seung-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.4
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    • pp.323-330
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    • 2007
  • Recently, due to the effective land utilization and environmental protection, the construction of 2-arch tunnel has been gradually increased. In spite of this tendency, the mechanical information for the 2-arch tunnel, especially such as its behavior characteristics and mechanism are not enough. Therefore in this study, the theoretical and numerical studies on the behavior characteristics of 2-arch tunnel are carried out and longitudinal optimum separated distance of tunnel face is proposed by considering the analysis results from the behavior of advanced excavation of tunnel and stress of central pillar. As a result, longitudinal optimum separated distance of tunnel face is in 0.5D for the better safety of 2-arch tunnel by rapidly decreasing the stress concentration of central pillar.

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Numerical simulation study on applicability of electrical resistivity survey at tunnel face (터널 굴착면에서의 전기비저항 탐사 적용성에 관한 수치해석 연구)

  • Yi, Myeong-Jong;Kim, Nag-Young;Lee, Sangrae;Hwang, Bumsik;Ha, Myung Jin;Kim, Ki-Seog;Cho, In-Ky;Lee, Kang-Hyun
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.24 no.3
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    • pp.279-292
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    • 2022
  • Unexpected anomalies in the geotechnical investigation at design stage may cause problems during tunnel excavation. Therefore, it is important to predict the ground condition ahead of a tunnel face during tunnel excavation in order to prevent tunnel collapse. Despite the fulfillment of an electrical resistivity survey at the tunnel face, the existing electrical resistivity survey program can produce distorted results by the limitation of tunnel modelling. In this background, this study develops a modelling program for an electrical resistivity survey considering the tunnel shape. Numerical simulation and inverse calculation were performed for the electrical resistivity survey in the tunnel using the developed program. As a result, it was proved that the developed program could predict accurately the anomalous object's location and condition ahead of the tunnel face.

A Theoretical and Numerical Study on the Effects of Prereinforcement of Tunnel Face (터널막장 선행보강 효과에 관한 이론적.수치해석적 연구)

  • 김광진;문현구
    • 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.

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