Hot on the heels of Herrenknecht‘s historic first breakthrough on the transalpine Gotthard running tunnels, (T&TI, October, p6), comes the news that a second Herrenknecht TBM has holed through to the Faido station on the scheme.
After driving over 14km, the hardrock gripper TBM, Heidi, broke through on 26 October “with a deviation of only a few centimetres”. The 8.83m diameter TBM was used to bore the west tube of the Gotthard Base Tunnel from Bodio where it started driving nearly four years ago in January 2003.
Boring through mountain geology broadly characterised as gneiss, granite and slate, the TBM achieved a best daily performance of 35m and a best weekly advance of 190.25m.
Operated by the TAT contractor consortium comprising Zschokke Locher AG, Hochtief AG, Alpine Mayreder Bau, CSC and Impregilo SpA, the TBM will be walked across the Faido station excavation and then used to bore the 14.6km long running west tunnel towards Sedrun. For this section Heidi and Sissi, the sister machine that broke through on 6 September, will be overhauled and have a 9.43m diameter cutting head installed to accommodate the required cut that takes account of the greater rock burden and consequently higher rock pressure for this leg. Excavation is due to restart in approximately six months
By 1 November, AlpTransit said over 66% of its Gotthard Base Tunnel had been excavated with over 100km of linear excavation of running tunnels, galleries and passages having been mined. For October, the total amount driven was 893m.
The two TBMs boring between Amsteg and Sedrun have also reached their destinations, six and nine months ahead of schedule. Work is now underway to dismantle them down to their component parts for demobilisation.
