Mixed Fortune at GotthardStretching 2 x 57 km between Erstfeld and Bodio, the Gotthard base tunnel will be the longest and deepest in the world. Of the total 153.3 km of access adits, shafts and main tunnels, 62.98 km or 41% had been excavated on 15th December, 2004. Four Herrenknecht Gripper TBMs are driving the main tunnels from north to south (section Amsteg) and from south to north (section Bodio/Faido). To date, 23.2 km of the overall 75 km to be driven by the TBMs has already been completed.On the north drives, the two 9.58 m-diameter Gripper TBMs (machines S-229 and S-230) of the AGN JV, including Murer and Strabag, have already driven half of the sections between Amsteg and Sedrun, each 11.35 km in length. In the east tube, the TBM 'Gabi I', which started excavation on 28th May, 2003, had completed half of the tunnel route on 17th November, 2004. In the west tube, its sister 'Gabi II', which commenced its job on 7th August, 2003, reached this intermediate point on 6th December, 2004. There is still approximately 5.4 km to go in the east tube and 5.6 km in the west tube up to the section limit in Sedrun. Good progress has been recorded on the north drives with best day figures of up to 40.1 m. Visit www.agn-amsteg.chWhereas the north TBM drives easily gained speed, the TAT JV had to face difficult ground on the southern route between Bodio and Faido with the other two Herrenknecht Gripper TBMs, 8.83 m in diameter. The TAT JV (Zschokke Locher, Hochtief, Alpine Mayreder, CSC and Impregilo) encountered geological fault zones earlier than expected, the 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 metre driven needs to be supported with steel arches. The TBM S-210 had driven and secured 5,765 m of the east tube in Bodio at end December 2004, with best weekly performance of 162.7 m since tunnelling started in January 2003. In the west tube in Bodio, the TBM S-211, which started excavation on 22nd February, 2003, had already completed 6,438 m of tunnel at the end of December 2004, with best weekly performances of up to 137.85 m. In the last few weeks, the machines were operating in coarse-grained gneiss with low to medium grade fracturing zones. Therefore, anchors, partial arches and wire mesh were used to secure the tunnel. Average daily performances of 14.2 m could be achieved in the east bore and 12.7 m in the west tube.AlpTransit now expects breakthrough in Faido in 2006 instead of 2005 as originally scheduled, since it is almost impossible to catch up the delay. Visit www.tat-ti.chAlthough there is still a long way ahead, great performances have already been achieved by and large. Subscribe to E-News Weekly 3/2005, 49/2004 & 46/2004. Visit www.alptransit.ch and www.herrenknecht.com 04/05. Click to enlarge