ABSTRACT
The New Tomei and New Meishin (Tokyo-Nagoya and Nagoya-Kobe, respectively) Expressways have been undertaken for their construction, which are commonly thought to become among Japan’s major arterial highways in the twenty-first century. The Hirakata Tunnel, with three traffic lanes and shoulders on one side, is located in the road section wedged between the Yawata Junction (Kyoto Prefecture) and the Takatsuki Junction (Osaka Prefecture) of the New Meishin Expressway. This paper presents the feasibility study results of the shield tunneling method, using the same design criteria as the non-circular, horseshoe section of mountain tunnel, to the equivalent section of the Hirakata Tunnel. Shield tunnels generally use the circular section for the construction in order to ensure their structural stability and economical design. As a feasibility study of the project tunnel, however, the economical horseshoe section has been chosen to examine in a similar way as mountain tunnels are examined. This is because the planned tunnel has various constraints for the construction and is to have large section of its required roadway space in lateral rectangular shape. The shield tunnel has the largest ever section (non-circle; excavation section area: approximately 190 m2), even larger than the existing world’s largest section (excavation section area: approximately 152 m2) of the Tokyo Bay Aqua-Line Tunnel, thus raising many relevant issues that has to be examined.
