• Title/Summary/Keyword: Tunnel displacement

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Tunnelling in Bangkok - Two Case Studies (방콕의 터널공사 - 두 개의 사례연구)

  • Teparaksa, Wanchai;Cho, Gye-Chun
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.2
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    • pp.153-163
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    • 2005
  • This paper presents two case studies for tunnelling in Bangkok: a subway tunnel site and a flood diversion tunnel site. The first case study is related to ground displacement response for dual tunnel Bangkok MRT subway. The MRT subway project of Bangkok city consists of dual tunnels about 20 km long with 18 subway stations. The tunnels are seated in the firm first stiff silty clay layer between 15-22 m in depth below ground surface. The behavior of ground deformation response based on instrumentation is presented. The back analysis based on plain strain FEM analysis is also presented and agrees with field performance. The shear strain of FEM analysis is in the range of 0.1-1% and in accordance with the results of self boring pressuremeter tests. Meanwhile, the second case study is related to the EPB tunnelling bored underneath through underground obstruction. The Premprachakorn flood diversion tunnel is the shortcut tunnel to divert the flood water in rainy season into the Choapraya river. The tunnel was bored by means of EPB shield tunnelling in very stiff silty clay layer at about 20-24 m in depth. During flood diversion tunnel bored underneath the existing Bangkok main water supply tunnel and pile foundation of the bridge, instrumentation was monitored and compared with predicted FEM analysis. The prevention risk potential by means of predicting damage assessment is also presented and discussed.

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Stability Estimation of NATM Tunnel due to Excavation using Back Analysis (역해석기법을 통한 NATM 터널의 안정성 평가)

  • Lee, Jae-Ho;Kim, Young-Su;Jin, Guang-Ril;Park, Jin-Kyu;Park, Si-Hyun;Choi, Chil-Yong
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.03a
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    • pp.494-504
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    • 2008
  • Successful design, construction and maintenance of NATM tunnel demands prediction, control, stability estimation and monitoring of surface settlement, gradient and ground displacement with high accuracy. Back analysis using measured data and forward analysis have been and are indispensable tools to achieve this goal. Sakurai provided the hazard warning levels for assessing the stability of tunnels using the relation of critical strain and apparent Young's modulus. This paper performed the estimation of tunnel stability on construction. Firstly, the apparent Young's modulus concept and back analysis method is introduced for the assessment of tunnel safety during excavation a brief framework. Secondly, this paper deals with case study using "Apparent Young's modulus" and "Back analysis" for the purpose of estimating the stability of NATM tunnel in Korea. Finally, a general method that can be estimated the tunnel stability discussed by a flow chart.

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Prediction methods on tunnel-excavation induced surface settlement around adjacent building

  • Ding, Zhi;Wei, Xin-jiang;Wei, Gang
    • Geomechanics and Engineering
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    • v.12 no.2
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    • pp.185-195
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    • 2017
  • With the rapid development of urban underground traffic, the study of soil deformation induced by subway tunnel construction and its settlement prediction are gradually of general concern in engineering circles. The law of soil displacement caused by shield tunnel construction of adjacent buildings is analyzed in this paper. The author holds that ground surface settlement based on the Gauss curve or Peck formula induced by tunnel excavation of adjacent buildings is not reasonable. Integrating existing research accomplishments, the paper proposed that surface settlement presents cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics when the tunnel is respectively under buildings, within the scope of the disturbance and outside the scope of the disturbance. Calculation formulas and parameters on cork distribution curve and skewed distribution curve were put forward. The numerical simulation, experimental comparison and model test analysis show that it is reasonable for surface settlement to present cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics within a certain range. The research findings can be used to make effective prediction of ground surface settlement caused by tunnel construction of adjacent buildings, and to provide theoretical guidance for the design and shield tunnelling.

Analytical behavior of longitudinal face dowels based on an innovative interpretation of the ground response curve method

  • Rahimpour, Nima;Omran, Morteza MohammadAlinejad;Moghaddam, Amir Bazrafshan
    • Geomechanics and Engineering
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    • v.30 no.4
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    • pp.363-372
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    • 2022
  • One of the most frequent issues in tunnel excavation is the collapse of rock blocks and the dropping of rock fragments from the tunnel face. The tunnel face can be reinforced using a number of techniques. One of the most popular and affordable solutions is the use of face longitudinal dowels, which has benefits including high strength, flexibility, and ease of cutting. In order to examine the reinforced face, this work shows the longitudinal deformation profile and ground response curve for a tunnel face. This approach is based on assumptions made during the analysis phase of problem solving. By knowing the tunnel face response and dowel behavior, the interaction of two elements can be solved. The rock element equation derived from the rock bolt method is combined with the dowel differential equation to solve the reinforced ground response curve (GRC). With a straightforward and accurate analytical equation, the new differential equation produces the reinforced displacement of the tunnel face at each stage of excavation. With simple equations and a less involved computational process, this approach offers quick and accurate solutions. The FLAC3D simulation has been compared with the suggested analytical approach. A logical error is apparent from the discrepancies between the two solutions. Each component of the equation's effect has also been described.

Analysis of pile group behaviour to adjacent tunnelling considering ground reinforcement conditions with assessment of stability of superstructures

  • Young-Jin Jeon;Cheol-Ju Lee
    • Geomechanics and Engineering
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    • v.33 no.5
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    • pp.463-475
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    • 2023
  • Tunnel construction activity, conducted mainly in mountains and within urban centres, causes soil settlement, thus requiring the relevant management of slopes and structures as well as evaluations of risk and stability. Accordingly, in this study we performed a three-dimensional finite element analysis to examine the behaviour of piles and pile cap stability when a tunnel passes near the bottom of the foundation of a pile group connected by a pile cap. We examined the results via numerical analysis considering different conditions for reinforcement of the ground between the tunnel and the pile foundation. The numerical analysis assessed the angular distortion of the pile cap, pile settlement, axial force, shear stress, relative displacement, and volume loss due to tunnel excavation, and pile cap stability was evaluated based on Son and Cording's evaluation criterion for damage to adjacent structures. The pile located closest to the tunnel under the condition of no ground reinforcement exhibited pile head settlement approximately 70% greater than that of the pile located farthest from the tunnel under the condition of greatest ground reinforcement. Additionally, pile head settlement was greatest when the largest volume loss occurred, being approximately 18% greater than pile head settlement under the condition having the smallest volume loss. This paper closely examines the main factors influencing the behaviour of a pile group connected by a pile cap for three ground reinforcement conditions and presents an evaluation of pile cap stability.

A study on stresses and displacements of the ground according to the closure ratio of tunnel face during tunnel excavation (터널 막장폐합비에 따른 지반 응력 및 침하량에 대한 연구)

  • Kim, Sang-Hwan;Min, Byeong-Heon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.12 no.5
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    • pp.369-378
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    • 2010
  • This paper presents a new approach of closing the tunnel face with sprayed concrete to reduce the stress at the tunnel face and displacement occurring at the ground surface during tunnel excavation. In order to carry out this research, the experimental and numerical studies are performed. In the experimental study, the model tests are carried out according to the closure ratio of tunnel face, tunnel depth and tunnel excavation length. The model test results are analyzed and interpreted by numerical calculation in order to verify both results obtained from experimental and numerical studies. It is clearly found that the tunnel face stability is decreased in decreasing the closure ratio of tunnel face. The results also show that the tunnel face is stable when the closure ratio of tunnel face is larger than 80%. This research will be very useful to develop the economical tunnel face closing system.

Elastic solutions for shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface

  • Wang, Ling;Zou, Jin-Feng;Yang, Tao;Wang, Feng
    • Geomechanics and Engineering
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    • v.19 no.3
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    • pp.201-215
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    • 2019
  • A new approach of analyzing the displacements and stress of the surrounding rock for shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface is investigated in this study. In the proposed approach, by using a virtual image technique, the shear stress of the vertical ground surface is revised to be zero, and elastic solutions of the surrounding rock are obtained before stress revision. To revise the vertical normal stress and shear stress of horizontal ground surface generated by the combined action of the actual and image sinks, the harmonic functions and corresponding stress function solutions were adopted. Based on the Boussinesq's solutions and integral method, the horizontal normal stress of the vertical ground surface is revised to be zero. Based on the linear superposition principle, the final solution of the displacements and stress were proposed by superimposing the solutions obtained by the virtual image technique and the stress revision on the horizontal and vertical ground surfaces. Furthermore, the ground settlements and lateral displacements of the horizontal and vertical ground surfaces are derived by the proposed approach. The proposed approach was well verified by comparing with the numerical method. The discussion based on the proposed approach in the manuscript shows that smaller horizontal ground settlements will be induced by lower tunnel buried depths and smaller limb distances. The proposed approach for the displacement and stress of the surrounding rocks can provide some practical information about the surrounding rock stability analysis of shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface.

굴착 진행과정을 고려한 터널 단면의 점탄성 및 탄소성 응력해석

  • Lee, Yeon-Gyu;Jang, Hyeon-Gon;Lee, Jeong-In
    • Proceedings of the Korean Geotechical Society Conference
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    • 1991.10a
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    • pp.152-165
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    • 1991
  • Elasto-plastic and Visco-elastic sytress analyses were conducted for standard cross-section of subway tunnel in Seoul . Considering the procedure of excavation and reinforcement, excavated region was divided to multiple elements. And the progress of tunnel is simulated to be the removal of a series of layerd elements by means of diminishing the stiffness of the portion progressively. Another method is to be free of stress due to excavation instead of stiffness. In the analysis multiple element method was conducted with ADINA program, the stiffness removal method was adopted . For the same model, stress release method was carried out with Visco-Elastic Analysis program developed in Rock mechanics laboratory, Seoul National University(SNU-VBA) . When upper tunnel excavated, displacements in roof were same for two results, but when bottom tunnel removed completely , displacement changes of rock in the stress release method exhibited very small amount compared with stiffness removal method.

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Damage Assessment of Buried Pipelines Due to Tunnelling (터널 굴착에 의한 지중 매설관의 손상평가)

  • 유충식;윤효석
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.11a
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    • pp.471-478
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    • 2000
  • Ground movements are inevitably caused by tunnel construction in soft ground. In the design and construction of tunnels in urban areas, the potential effects of buried pipelines by ground movements are one of the important design cosiderations. Generally, the most common modes of failure of buried pipelines due to ground movements are tensile fracture of main pipelines, rotation angle and pull-out displacement at joints. In the parametric study, a wide range of conditions were considered, including tunnel diameter(D), tunnel depth(Z$\sub$0/), volume loss(V$\sub$ι/) and inflection point(i). Based on this results, design charts, which are applicable to assess potential damage of buried pipelines associated ground movements due to tunnelling, are developed.

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Seismic Analysis of Tunnel Response by Response Displacement Method (응답변위법에 의한 터널의 내진해석)

  • Yun, Se-Ung;Shin, Jong-Ho;Park, Du-Hee
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.09a
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    • pp.457-462
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    • 2009
  • In this study, seismic analysis is performed using simplified method, analytical solution and numerical analysis based on one-dimensional seismic site response analysis. The results show that analytical solution of tunnel response is predicted more conservative than numerical solution. And simplified method is not appropriate for seismic analysis of tunnel response. In addition, it is reasonable to determine shear-modulus reduction ratio performing seismic site response analysis to consider ground nonlinear-behavior.

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