September 1st saw breakthrough achieved on the Aarau East Circular Road Tunnel in Switzerland.
The 60m long, 10m diameter tunnel constructed by JV Zschokke took 10 months to complete and demanded a strict settlement control. The tunnel passes beneath one old and a newer building with only 3m cover in alluvial, partly running sand. An on-line monitoring system recorded limited settlements of 12mm.
Excavation was achieved by installing a 15m long pipe umbrella at the top with jetting at the sides. A 1m advance was adopted with immediate thin shotcrete application, to prevent the sands from running, followed by a second layer of fibre reinforced shotcrete. Finally the sides were excavated and shotcreted with invert excavation and ring closure completing the process.
Consultant to the project, Dr Werner Heierli of Heierli Consulting Engineers told T&TI: " This construction procedure allowed to completely forgo the use of steel support arch girders, lattice girders or reinforcement meshes. Limited settlement was achieved by consistent support of the tunnel vault or its portions down to solid ground in every of the many construction phases."
A full report of the project will appear in a forthcoming issue of T&TI.
