ABSTRACT
At the Kobe Nagata Tunnel in Japan, four evacuation tunnels that will be connected to existing two main tunnels are planned to be excavated by the conventional tunneling method. The main tunnels were constructed about twenty years ago. After the Sasago tunnel accident where ceiling boards fell onto passing vehicles, ceiling boards in the Kobe Nagata Tunnel were removed and the ventilation system was changed accordingly. Therefore, additional evacuation tunnels must be constructed in operating tunnels. Two of the four tunnels are watertight and water cut-off grout injection will be done. Prior to excavation of the evacuation tunnels, the existing lining concrete and tunnel supports should be removed. Since the loads are acting on these existing structures, pre-reinforcement for the lining concrete around the opening is required against the loads. This paper shows an unprecedented design and construction method of opening up the lining concrete subjected to high pressure.
