Case study of huge squeezing behavior in expressway tunnel in service

The Sakazuki-yamaTunnel (inbound lane tube 1,234mlong) on theYamagata Expressway was opened to service on 20 July 1991. In the construction of this tunnel excavated in rhyolitic tuff, serious problems occurred such as convergence as large as 300mm due to water ingress and swelling minerals. Almost 17 years after the opening, the road surface suddenly heaved, and the upheaval reached 250mm the next day, and 380mm after 11 days. The inbound lane tube was closed one week after the occurrence of the damage, and the adjacent outbound lane tube was used for two-way traffic. The restoration plan was to remove damaged invert and construct an invert of higher load-carrying capacity as soon as possible. The upheaval of the invert was 950mm at maximum. Such a large deformation and failure of the road surface and invert, which occurred a long time after completion of the tunnel, was an unprecedented event in Japan. In the short period of three and a half months after the occurrence of the damage, the new invert, pavement and facilities were all constructed, and the tunnel was reopened to traffic on November 28. Consequently, the function of the expressway, an important infrastructure element, was restored before the heavy snow season (December).