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  Case study of a tunnel with time-dependent behaviour in a volcanic area of Hokkaido

  Records of the construction and repair of a tunnel with time-dependent deformation were analysed to clarify the mechanism and to construct judging method of time-dependent deformation part. As a result, it was inferred that release of in situ stress of rock converged for about 80 days and time-dependent deformation resulted from rock degradation by the change of rock surroundings mainly with groundwater inflow. It was confirmed that the score of tunnel face estimation could not separate with and without time-dependent deformation part clearly. Although the displacement value at the part of time-dependent deformation of the tunnel had a tendency to be larger than those at the part without deformation, the boundary value was too small (about 4mm of crown settlement) to be adopted as threshold to determine tunnel support patterns. By re-examination of geological description of samples of advanced drilling at the time of construction, it was verified that the geological description with time-dependent behaviour should be more respected to predict time-dependent deformation parts.

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