Perpustakaan Digital ITB

This paper compares sequential excavation methods for a large cross-section twin-tunnel in soft ground condition, speci?cally, the Yogyakarta-Bawen highway twin tunnels. The tunnels are horseshoe- shaped with the dimension of 20.18 m x 13.7 m and under a maximum cover depth of only 32 m to tunnel roof. Based on an analysis of three sequential excavation methods, the side drift method yields the most effective way of controlling the roof settlement (3 cm) compared to the three-bench seven step method (6 cm) and the combination of side drift and top-heading and bench method (5 cm). The side drift method also generates the arch ef feet close to the excavation perimeter, resulting in a strength factor of more than 1.5 at the wall and roof of the tunnel, while at the same time minimizing the plastic zone thickness to only 2 m at the invert.