The construction team on Switzerland’s 4.4km long twin tube Uetliberg road tunnel celebrated a double land mark recently when core bore excavation was completed on the 240m long Diebis soil section allowing access for the start up of the 5m diameter pilot bore TBM on the main 2.8km long hard rock northern tunnel tube.
The Uetli JV started construction of the 148m2 Diebis soil section from the Ettenburg side of the tunnel in Spring 2001 using a sequence of side drifts, top heading, bench and invert. The JV used excavators to drive through the base moraine overlain with slope wash, all constructed under groundwater. The section is supported by steel segments with 250mm thick steel fibre reinforced shotcrete layers and will feature a concrete final lining with a plastic membrane for waterproofing.
Completion has allowed the Uetli JV to take the 5m diameter pilot drive TBM to the face of the 2.8km long northern tunnel drive that starts where the Diebis section ends. The machine arrived ready to start boring through the Uetliberg molasse on 8th May. The schedule is set so that the pilot TBM can be returned to the start of the southern tube to begin boring in November 2002 and complete in July 2003.
Whilst the TBM bores the 5m diameter southern pilot tube the northern pilot will be widened to the required 14.2m-14.4m diameter using a tunnel bore extender (TBE) between October 2002 and March 2003. Upon completion the TBE will return back to the end of the Diebis section and widen the southern tube starting in May 2004 with completion scheduled for September 2005.
The complete $687.5M Uetliberg tunnel is being built for the client Baudirektion des Kantons Zürich to link the Birmensdorf bypass in the west with the Zurich-Chur highway in the east. Swiss company, Amberg Consulting Engineers is providing complete consultancy services to the client.
