• Title/Summary/Keyword: tunnel face

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Influence of Weak Ground Ahead of the Tunnel Face on 3D-displacement and Face Extrusion (막장전방의 연약층이 터널 3차원변위 및 막장 수평변위에 미치는 영향)

  • Jeon, Je-Sung
    • Journal of the Korean Geotechnical Society
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    • v.19 no.6
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    • pp.189-206
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    • 2003
  • During tunnel excavation in urban area a systematic monitoring is important for the purpose of determination of support type and quantity, as well as for the control of stability of both surface structures and the tunnel itself due to the frequently, and in many cases, abruptly changing ground condition. In Austria absolute displacement monitoring methods have replaced relative displacement measurements by geodetic methods to a large extent. Prompt detection of weak ground ahead of the tunnel face as well as better adjustment of excavation and support to the geotechnical conditions is possible with the help of the improved methods of data evaluation on sites. Deformation response of the ground to excavation starts ahead of the tunnel face, therefore, the deformation and state of the tunnel advance core is the key factor of the whole deformation process after excavation. In other words, the rigidity and state of the advance core play a determining role in the stability of both surface structures and the tunnel itself. This paper presents the results from detailed three-dimensional numerical studies, exploring vertical displacements, vector orientations and extrusions on tunnel face during the progressive advancement for the shallow tunnel in various geotechnical conditions.

Commentary on Soft Ground TBM Tunnel Face Support Calculation Methods (연약지반 TBM 터널 막장지보 계산방법 해설)

  • Jee, Warren Wangryul;Yoo, Jung Hyun
    • Tunnel and Underground Space
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    • v.28 no.2
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    • pp.186-192
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    • 2018
  • The German Tunnelling Committee (DAUB) recently published new recommendations for face support calculations; Zdenek Zizka and Markus Thewes of Ruhr University Bochum actively discuss and explain these new recommendations where these recommendations are intended to assist in choosing between various calculation methods which are also dependent on ground conditions. The guidelines also discuss important scientific approaches with face stability calculations, mainly those due to earth pressure and groundwater pressure on the tunnel face. This paper aims to explain these recommendations through Zdenek Zizak and Markus Thewes's discussion on these Tunnel Face Support Calculation Methods.

Behavior of a tunnel face reinforced with longitudinal pipes - laboratory investigation (실내실험에 의한 수평보강재로 보강된 터널막장의 거동)

  • Yoo, Chung-Sik;Yang, Ki-Ho
    • 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.

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The Study On The Pre-displacement Before Face Of The Shallow Tunnel In The Weathered Soil (풍화토구간을 통과하는 천층터널의 막장선행변위에 대한 연구)

  • Kang, Suk-Ki;Yoon, Ju-Sang
    • Proceedings of the KSR Conference
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    • 2008.11b
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    • pp.947-954
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    • 2008
  • Nowadays many urban subways are frequently constructed under the building and the river by the use of tunneling method. Especially, the majority of the tunnel are constructed even with shallow depth under the ground in the weathered soil. Since the tunnel are generally designed on the basis of the geographic soil investigation, the stability of the tunnel should be checked with the realistic data instrumented during construction. The displacement of the tunnel occurs in front of the end face during the excavation of the tunnel, which is called as pre-displacement. The total displacement can be figured from the exact pre-displacement, which is very difficult to measure without using any device installed in front of the tunnel end face. In this study, the pre-displacement measured from horizontal inclinometer was analyzed to know the co-relation with the total displacement and also, the trend and the characteristics of the tunnel deformation during construction was suggested through the regression analysis of the measured data.

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A Study on Problems and Improvements of Face Mapping during Tunnel Construction (국내 터널시공 중 막장지질조사의 문제점 및 개선방안에 관한 연구)

  • Kim Kwang-Yeom;Kim Chang-Yeng;Yim Sung-Bin;Yun Hyun-Seok;Seo Yong-Seok
    • The Journal of Engineering Geology
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    • v.16 no.3 s.49
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    • pp.265-273
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    • 2006
  • Face mapping during tunnel construction is useful and critical to predict the characteristics and stability condition of following tunneling sections and to select optimum support pattern. Therefore, a detailed geological survey of the tunnel faces, as important as a routine underground survey and a RMR evaluation, should provide critical information of the tunnel face condition in terms of the engineering geological condition and the safety of working environment for the following tunneling section. But the results of the face investigation have not been applied satisfactorily during tunneling due to limitation of technique, experience and time. This study analyze problems of face mapping in tunnel construction site by using statistical results of face mapping sheets obtained from completed tunnels, and suggest several opinions to improve face mapping during tunnel construction.

An investigation on tunnel deformation behavior of expressway tunnels

  • Chen, Shong-Loong;Lee, Shen-Chung
    • Geomechanics and Engineering
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    • v.21 no.2
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    • pp.215-226
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    • 2020
  • The magnitude and distribution of tunnel deformation were widely discussed topics in tunnel engineering. In this paper, a three-dimensional (3D) finite element program was used for the analysis of various horseshoe-shaped opening expressway tunnels under different geologies. Two rock material models - Mohr-Coulomb and Hoek-Brown were executed in the process of analyses; and the results show that the magnitude and distribution of tunnel deformation were close by these two models. The tunnel deformation behaviors were relevant to many factors such as cross-sections and geological conditions; but the geology was the major factor to the normalized longitudinal deformation profile (LDP). If the time-dependent factors were neglected, the maximum displacements were located at the distance of 3 to 4 tunnel diameters behind the excavation face. The ratios of displacement at the excavation face to the maximum displacement were around 1/3 to 1/2. In general, the weaker the rock mass, the larger the ratio. The displacements in front of the excavation face were decreased with the increasement of distance. At the distance of 1.0 to 1.5 tunnel diameter, the displacements were reduced to one-tenth of the maximum displacement.

Electrical resistivity tomography survey for prediction of anomaly in mechanized tunneling

  • Lee, Kang-Hyun;Park, Jin-Ho;Park, Jeongjun;Lee, In-Mo;Lee, Seok-Won
    • Geomechanics and Engineering
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    • v.19 no.1
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    • pp.93-104
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    • 2019
  • Anomalies and/or fractured grounds not detected by the surface geophysical and geological survey performed during design stage may cause significant problems during tunnel excavation. Many studies on prediction methods of the ground condition ahead of the tunnel face have been conducted and applied in tunneling construction sites, such as tunnel seismic profiling and probe drilling. However, most such applications have focused on the drill and blast tunneling method. Few studies have been conducted for mechanized tunneling because of the limitation in the available space to perform prediction tests. This study aims to predict the ground condition ahead of the tunnel face in TBM tunneling by using an electrical resistivity tomography survey. It compared the characteristics of each electrode array and performed an investigation on in-situ tunnel boring machine TBM construction site environments. Numerical simulations for each electrode array were performed, to determine the proper electrode array to predict anomalies ahead of the tunnel face. The results showed that the modified dipole-dipole array is, compared to other arrays, the best for predicting the location and condition of an anomaly. As the borehole becomes longer, the measured data increase accordingly. Therefore, longer boreholes allow a more accurate prediction of the location and status of anomalies and complex grounds.

Supporting The Tunnel Using Digital Photographic Mapping And Engineering Rock Classification (디지털 사진매핑에 의한 공학적 암반분류와 터널의 보강)

  • Kim, Chee-Hwan
    • Tunnel and Underground Space
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    • v.21 no.6
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    • pp.439-449
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    • 2011
  • The characteristics of rock fractures for engineering rock classification are investigated by analyzing three dimensional point cloud generated from adjusted digital images of a tunnel face during construction and the tunnel is reinforced based on the supporting pattern suggested by the RMR and the Q system using parameters extracted from those images. As results, it is possible saving time required from face mapping to tunnel reinforcing work, enhancing safety during face mapping work in tunnels and reliability of both the mapping information and selecting supporting pattern by storing the files of digital images and related information which can be checked again, if necessary sometime in the future.

Seismic stability analysis of tunnel face in purely cohesive soil by a pseudo-dynamic approach

  • Huang, Qi;Zou, Jin-feng;Qian, Ze-hang
    • Geomechanics and Engineering
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    • v.23 no.1
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    • pp.1-13
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    • 2020
  • To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

A Pilot Study of Stiffness Mesurements for Tunnel-Face Materials Using In-hole Seismic Method (인홀 시험을 이용한 터널 막장의 암반강성 측정에 대한 적용성 연구)

  • Mok, Young-Jin;Kim, Young-Su
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.445-456
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    • 2005
  • The research concentrates on improving the in-hole seismic probe, which has been developed in past five years, to be used in stiffness measurements of tunnel-face materials. The probe was down-sized to be fit in 45-mm diameter holes(or BX) drilled by a jumbo-drill, which is used to drill holes to install explosives for tunneling. Also trigger system was improved by using a down-speeding motor for operating convenience and air packing system was replaced with a set of plate-springs to eliminate supply of compressed air. These modifications are to adjust the probe for the unfavourable environment inside of tunnels and to test without any further drilling cost. The probe and testing procedure were successfully adopted with horizontal holes drilled by a jumbo-drill at a tunnel-face to evaluate the stiffness of rock mass. The measured shear wave velocities can be used to estimate deformation properties of rock mass for tunnel analyses.

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