The Sakazuki-yama Tunnel (inbound lane tube 1,234 m long) on the Yamagata 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 300 mm due to water ingress and expansive mineral.
Almost 17 years after the opening, the road surface suddenly heaved, and the upheaval reached 250 mm the next day, and 380 mm 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 950 mm 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).