Abstract: In the tunnel excavation construction in the mountain area, the conventional excavation sequence is started from the outside of the mountain. The access road and the excavation platform are necessary and these auxiliary facilities are resulted in large disturbance at the portal of the tunnel. A new tunnel excavation method, which is excavated from inside of the tunnel towards the exit, was applied in the water tunnel exit portal in NJ Hydraulic Electricity Project. The advantages of this method are the following: the disturbance to the adjacent area of the exit portal is significantly reduced; the cost for the purchase of the required property around the portal area is reduced; and the construction safety is also improved.

Key words: N-J Project, Thin Overburden, Exit Portal, Tunnel Excavation