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Study of the Effect of Central Beam Column (CBC) Structure on Sequential Excavation of Large Span Underground Station

Valizade Givi, Amir | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40441 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mehdi
  7. Abstract:
  8. Effect of utilizing Central Beam Column (CBC) structure on shallow, large span underground spaces excavation is studied. The CBC method focuses on increasing the overall rigidity of tunnel supporting system prior to full face excavation, in which central drift excavation is limited to the dimensions of the central beam and column to reduce disturbances. Constructing the central beam and column structure, the excavation is completed with NATM excavation method in a symmetric manner about centerline. In CBC method on each side of the centerline there is an arch structure composed of the initial lining resting on roof beam on top and bottom beam at the invert. The roof and bottom beams take the thrusts from the adjacent arches and span to columns located at the center of the platform. The structure consisting of the roof and bottom beams and columns is referred to as CBC Structure which due to its higher rigidity, reduces surface settlement and helps to maintain the stability of underground space. The general soil structure behavior related to final settlement and stress distribution is analyzed using 3-D numerical analyses in soils modeled with Mohr–Coulomb elasto-plastic constitutive equation with the finite element Abaqus software. The model takes advantage of the symmetry of the problem and the sequential excavation is modeled analogous to real construction sequence with 1 meter excavation length. In CBC method, effect of the stiffness, dimensions and the spacing of CBC structure is studied and using columns 1x1 meter cross section with 10 meter spacing is proposed as yielding the best results. Parametric studies on soil prosperities and study of different face advancement is also performed. For comparison with other pre supporting methods available for settlement control, consolidation grouting was also modeled. The results show the effect of the CBC structure on the ground surface settlement and stress redistribution on supporting system and overburden soil is more pronounced than other high cost pre-supporting systems.

  9. Keywords:
  10. Three Dimensional Modeling ; ABAQUS Software ; Ground Surface Settelment ; Tunneling Induced Settlement ; Surface Settlement Control ; Central Beam Column Presupport

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