Investigation into loosened zones and deformation behaviors of a tunnel in a squeezing ground by means of the multiple-layer supporting method

Iiyama Tunnel is a 22.2 km-long railway tunnel for Hokuriku Shinkansen (bullet train) Line that runs from Iiyama City of Nagano Prefecture through to Itakura Town of Niigata Prefecture in Japan. It is under construction with six work sections. Konari work section (3.8 km in length) is mainly in Neogene Siiya formation mudstone where large convergences more than 200 mm have occurred in sections of the overburden exceeding 200 m. In such a squeezing ground, the multiple-layer supporting method has been applied for the tunnel construction. The first layer support is left to deform while taking the loss of its soundness into account and relatively large deformation is allowed. Subsequently, the second layer support (and further layers if necessary) is applied in the interior side so that the soundness of the most-inner-layer support may be secured. The work execution procedures together with the support patterns are discussed. In the heading of Niigata side, the squeezing phenomena including large deformation of the convergence up to 450 mm and the support failure was observed. In order to understand the behavior of the ground and support, seismic exploration was performed to detect the loosened zones. It was found that the velocity-reduced strata, which would correspond with the loosened zones, of significant thickness up to 8 m were developed around the tunnel. Three-dimensional elasto-plastic numerical analyses were carried out in which the work execution procedures were faithfully incorporated and the yielding behavior of the support members was taken into account. The results of the numerical analyses successfully simulated the behaviors of both the ground and supports measured in situ. For example, the hoop stresses of shotcrete at the crown are given in Fig. 2; the analysis results agreed well with the stress changes measured. The plastic zones of shotcrete whose distribution was quite similar to the observed failure pattern were obtained from the analysis. (A). "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • Authors:
    • TAKETSU, E
    • MORITA, R
    • AOKI, T
  • Publication Date: 2004-7


  • English

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  • Accession Number: 01011583
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:19PM