The Minoh toll road mountain tunneling project (southern lot) includes construction of a main tunnel (2000 meters long), an evacuation tunnel (2009 meters long), a working tunnel (354 meters long) and crosscuts. The south entrance of the main tunnel, which connects with the on-off ramps, has an extremely large section exceeding 300 square meters at maximum. Since the geology is complex, the face was extremely unstable during excavation of the working tunnel with a significant volume of water inflow in many places. Various auxiliary methods were applied for the construction of a working tunnel to verify the suitable method for the main tunnel. This paper evaluates various auxiliary methods used in the working tunnel construction, focusing upon the effect of new injected long face reinforcement, and presents the design principle of the main tunnel.
