Bored tunnel lining design in soft soils - a comparison between analytical and numerical analyses

In Singapore, most of the recent major public infrastructures are constructed underground to minimise land usage. This includes mass rail transit system with capacity up to 20,000 passengers. This paper will present the tunnel lining design carried out for the on-going Singapore MRT Circle Line Stage 2 - Contract 823 project. The twin-bored tunnels will be constructed in very soft marine clays. A cost-effective and practical design has been formulated. Analytical analyses using the Bedded Beam Model by Duddeck and Erdmann (1982), as well as numerical analysis were conducted for the bored tunnel lining design. The merits of each analysis will be discussed and compared in this paper. The geotechnical and structural design parameters adopted for the analyses will also be described and evaluated in the paper. Results showed that the analysis using the Bedding Beam Model give larger results compared to finite element model. These differences are due to the Bedding Beam Model is a structural design model which is subjected sorely to the vertical and horizontal loads. The stress and moments developed in a lining are dependent on the stiffness of tunnel lining relative to the soil, there is no structure-soil interaction. It is noted that the maximum bending moment is controlled by the flexibility ratio EcR3/EJ. For a larger value of flexibility ratio (large soil modulus), the moment becomes very small. Conversely, for a small value of flexibility ratio (relatively rigid lining), the moment is large. FEM able to model construction sequences and soil-structure interaction was considered. This soil-structure interaction capability in the FEM analysis caused the results to be smaller than analytical method due to soil arcing effect. The soil will transfer part of active pressure by arcing and the tunnel lining gets relative smaller pressure, this arcing effect will be larger if the soil surround the tunnel is stiffer according to Vermeer (2001). Results also show results for cases where tunnel lining was analysed with segmental joints, the bending moment and shear force are smaller compared to tunnel lining that modelled as a complete ring. This result suggests that if the segmental joints were considered in the FEM analysis, the bending moment and shear forces will reduce to about half of the value compared to the analysis without considering segmental joint. These results is reasonable as the segmental joints having a smaller stiffness compared to concrete lining, which caused smaller bending moment and shear stress. (A). "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • Authors:
    • CHONG, P T
    • TANG, S K
    • LIM, T L
    • SUGAWARA, S
    • FURUSONO, T
  • Publication Date: 2004-7

Language

  • English

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Filing Info

  • Accession Number: 01011618
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:21PM