Abstract
The Aki-Fuchu twin tunnels on the Hiroshima Expressway No.1 have two lanes each, with 30 to 40 m overburden. The geology of that region is composed of heavily weathered granite and diorite, which are extremely decomposed due to deep weathering. Therefore, the tunnel face is unstable and the convergence is noticeable. For ensuring face stability, tunneling is advanced with long face forepiling using glass fiber reinforced plastic tubes. The long face forepiling has found wider applications these days. However, almost no quantitative measurement data are available at present. In this context, the authors determined the ground behavior by measuring the axial force in the long face forepiles and the displacement ahead of the face, and quantitatively evaluated the effect of this technique by conducting numerical analysis.
