In Switzerland, on 6 July the second tube of the 11.8m diameter Islisberg tunnel (T&TI, June 2005, p8) was holed through by Herrenknecht’s single shield hard rock TBM after 4,666m of boring.
The Zurich municipality employed the consortium Ingeieurgemeinschaft N4.1.6 as consultants, comprising Poyry Infra AG, Dr.Vollenweider AG and Ernst Winkler + Partner AG. Arbeitsgemeinschaft ARGE Islisbergtunnel was appointed as contractor for the motorway tunnel scheme that has twin 4,955m long tubes, both driven by the same Herrenknecht machine. The ARGE consists of Marti Tunnelbau AG from Bern, Ed Zublin AG of Stuttgart and Marti AG Bauunternehmung from Zürich.
Excavation of this second tube got underway in mid-2005 along an alignment with geology characterised as “upper freshwater molasses”, or calcareous siltstones, fine layers of sand. T&TI was told that the best weekly performance was 112m of advance and Herrenknecht was keen to praise the consistently good performances recorded by the tunnelling teams who maintained an average 100m per week since the third week of the bore. The pre-cast concrete segmental lining installed with advance consists of five segments plus one key. A waterproofing PVC membrane is installed and the lining is completed with a concrete tunnel lining.
This TBM and site team also drove the first, 4,680m long western tube of the scheme, which broke through in spring 2005. The JV launched the TBM on 7 April 2004 following contract award in late spring 2003. Taking one year to complete, the team averaged an advance rate of 103m per week on the first tube, based upon a five day working week.
T&TI was told by Poyry that a low budget and tight timescale were significant challenges for builders of the scheme. The US$457M project was funded 80% by the state and 20% by Zurich municipality.
