Japan Highway Public Corporation (JH) Shizuoka Construction Bureau is now building the Kanaya tunnel in the New Tomei Expressway (New Tomei) in Shizuoka Prefecture. In the mudstone layer where the overburden is deep and competence factor is under 2, excessive internal displacement and foot settlement were observed, together with rock bolt failure and cracks in sprayed concrete. After high tensile strength bolts (748 kN) were introduced instead of rock bolts, displacement was well controlled and strength of the tunnel was enhanced.
This paper describes the characteristics of displacement behavior of a tunnel with large cross sectional area and applications of the high tensile strength bolts as a countermeasure for the displacement, based on the experience of western section of Kanaya Tunnel construction in mudstone layer.