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  Case study of the deterioration factors of pyroclastic rock and the measurement results of the time dependence deformation of tunnel

  The tunnel deformation, such as heaving or pushing out of the tunnel lining sometimes comes to occur after completion inside the tunnel that was constructed in the area of the pyroclastic rock with hydrothermal alteration. It is a big problem from the viewpoint of safe relief of the community, convenience and countermeasures cost. In this study, geological properties of deformed zone where occurred the heaving of tunnel were compared with its construction records after tunnel commencing services at pyroclastic rocks area in Hokkaido in Japan. The characteristics of rock minerals were also analyzed by the observation of thin section, X-ray diffraction. As a result of study, the speed of the tunnel heaving based on the measurement results were 6-71 mm/month for a short term in 15-21 mm/year in a long term. These values are available as an aim to estimate the limitation time to need countermeasures. The combination of rock minerals was indicated as an index to predict the deterioration of the rock for the long term.

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