The Otaru-Yoichi Section of the Trans-Hokkaido Expressway (23.4 km; tentaively 2-lane expressway) will run between the Otaru JCT (tentative name) of the Sasson Expressway and Yoichi IC (tentative name). It is scheduled to open in FY2018. Mt. Tenguyama (elev. 532 m) is an iconic mountain in Otaru city. The Otaru Construction Office, Hokkaido Regional Head Office of the East Nippon Expressway Co., Ltd. has been constructing the 2,978-m-long Mt. Tengyama Tunnel under the mountain. Approximately 600 m of excavation was complete as of May 2014. We adopted the All Ground Fastening (AGF) method as an auxiliary construction method with the aim of minimizing the loosening of bedrock during excavation immediately beneath landslide ground, and we adopted the minibench cut method for excavation. To monitor the ground conditions, we measured ground surface displacement and tunnel convergence.

This report gives an overview of the tunneling work and of the planing and actual construction with the auxiliary method.

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