Tunneling Gotthard makes progress

Schwanau, Germany – Both Herrenknecht Gripper TBMs, S-229 and S-230 (diameter 9.58m), of the JV AGN (Murer AG, Strabag AG) have already driven half of the sections between Amsteg and Sedrun, each 11.35km in length. In the eastern tube the tunnel boring machine ‘Gabi I’ (start of excavation on May 28, 2003), completed half of the tunnel route on November 17, 2004. In the western tube its sister machine ‘Gabi II’ (start of excavation on August 7, 2003), reached this intermediate point on December 6, 2004. Up to the section border in Sedrun, approximately 5.4km still have to be excavated in the eastern tube, and 5.6km in the western tube. Best daily performances of up to 40.1m underline the good progress in the north.

Whereas the TBM drives in the north could easily gain speed, the client AlpTransit Gotthard AG, the JV TAT and both Herrenknecht Gripper TBMs (diameter 8.83m) had to face ‘difficult’ mountain stretches on the southern route between Bodio and Faido. The JV TAT (Zschokke Locher AG, HOCHTIEF AG, Alpine Mayreder Bau GmbH, CSC Impresa Costruzioni SA; Impregilo S.p.A.) encountered geological fault zones earlier than expected: so-called kakirites. These fault rocks are too soft for both machines that are designed for high rock strengths and makes good TBM performances almost impossible. With great effort, each tunnel meter driven needs to be re-secured e.g. with steel arches.

In the meantime, the Herrenknecht Gripper TBM, S-210, has driven and secured 5,765m of the eastern tube in Bodio (status end of December 2004). The tunnel boring machine achieved a best weekly performance of 162.7m since tunnelling started in January 2003. In the western tube in Bodio the Gripper TBM, S-211, of the same construction type has also been boring and securing its way through the mountain. It started excavation on February 22, 2003 and has already excavated 6,438m of tunnel by the end of December 2004. The tunnel boring machine reached best weekly performances of up to 137.85m. In the last few weeks the machines were operating in coarse-grained gneiss with low up to medium-grade fracturing zones. Thus anchors, partial arches and wire mesh were used to secure the tunnel. Average daily performances of 14.2m could be achieved in the eastern and 12.7m in the western tube.

In Faido the AlpTransit now expects breakthrough in 2006 and not – as originally scheduled – in 2005, since it is almost impossible to make up for lost time. Although a long and rocky ‘road’ still lies ahead, great performances have already been achieved by and large. At the end of 2004 more than 40 % of the approximately 153 kilometers of shafts, pits and tunnel tubes of the Gotthard Base Tunnel were excavated. During the Holidays, the construction sites of the AlpTransit Gotthard AG in Erstfeld, Amsteg, Sedrun, Faido and Bodio/Pollegio are closed. The works at the construction project of the superlative start with renewed vigor at the beginning of 2005.

Auteur: Redactie Infrasite

Bron: Herrenknecht AG Tunnelvortriebstechnik