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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

The assessment of influences on ground due to 2nd tunnel excavation based on 1st tunnel excavation

The improvement of Japanese expressway capacities to be a high standard performance is currently executed to accommodate an enlargement of vehicle numbers and an increase of traffic density. Tunnels in those expressways are usually two-lane, therefore, it is necessary to construct new tunnels having two-lane parallel to the existing ones in close-distance to compose four-lane expressway. Taking into account the stability of the close-distance of parallel tunnels and economic issues, in addition to accommodate the use of space, effects of construction of a new tunnel (called as 2nd tunnel) on ground surrounding as well as an existing tunnel should be carefully examined. Moreover, it is not only taking a consideration on the 2nd tunnel stability but the examination should ensure safety of the existing tunnel, i.e., refer as 1st tunnel, during its service. The distance between two tunnels was commonly designed about 3D between central of the 1st and the 2nd tunnel (D: tunnel diameter) in which based on experiences that effects would not expand to the existing tunnel. However, the recent record data of some 2nd tunnel constructions has shown a contrary of this assumption. A new technique of assessment of influences of the 2nd tunnel construction on the 1st stage tunnel and ground surrounding is proposed in order to determine a sufficient distance between two tunnels by considering on a degree of interaction between them from a viewpoint of plastic region sizes. This study focused on sizes of each plastic region created during the 1st tunnel and 2nd tunnel construction. It was followed with an attempt to obtain a new method for predicting the influences of the 2nd tunnel excavation on surrounding ground, nevertheless to the 1st tunnel using an approach of a degree of interference of both plastic regions. In a case of both plastic regions do not impede each other, the independency of both tunnels is maintained. It means a possibility of a development of effects on the 1st tunnel due to the 2nd tunnel construction is small. Conversely, when it is interfering, the influence will be appearing on the 1st tunnel any time when the 2nd tunnel is in excavation process. Features of the proposed assessment method are shown below: 1. It is possible to compare the plastic zone of the 1st tunnel and the 2nd tunnel continuously along the tunnel axis, and the degree of the influence can be continuously presumed. 2. It is possible to evaluate the installation of the support structure of the 1st tunnel and its adoption method. 3. The boundary of influence of the 2nd tunnel can be assumed along the tunnel alignment with using the construction data of the 1st tunnel. 4. It is possible to examine the support pattern design of the 2nd tunnel. Moreover, it is also possible to obtain standard management during the construction. The study has shown that in the management system of the second tunnel construction, a practical viewpoint should carefully be considered as basic data in design stage of the second tunnel. Moreover, it is necessary to perform verification in realistic way, whether a setting value is appropriate by the measurement under construction etc. Furthermore, it is necessary to adopt a standard value for each tunnel with an implication of the maximum permissible convergence for the tunnel lining. (A). "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • Authors:
    • JUNICA, M I
    • AOKI, K
    • IWAI, K
    • SHINJI, M
    • NAKAGAWA, K
  • Publication Date: 2004-7

Language

  • English

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Filing Info

  • Accession Number: 01011607
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:20PM