ABSTRACT
The Second East Meishin Expressway, parts of which are under construction work in different locations in Japan today, is expected to play the role of a trunk line of future transportation. The road is of such high specifications that it has six lanes (or three vehicle lanes on one side) and provided with a berm on both sides throughout the route. Therefore, tunnels need an extremely large cross section of 180 square meters for excavation, and a Tunnel Boring Machine (TBM) Pilot Drift Widening technique is adopted in the Rittou tunnel. Although the TBM method is featured by its high construction speed compared with the NATM technique, a number of delayed construction cases are reported in which TBM excavation is suspended due to geological trouble under complicated Japanese geological conditions. In this context, the authors developed a construction system before starting TBM construction. The system is based on observational construction management mainly forward prediction combined with auxiliary techniques to ensure prompt and continued excavation without suspending TBM operation even in areas of bad earth quality. As a result, we could take proper measures promptly when poor geological quality was encountered so that we could complete the excavation of approximately 2,600m at a satisfactory mean monthly progress of 338m without experiencing remarkable trouble, and thus the effectiveness of this technique has been confirmed.
