Switzerland – Gotthard Base Tunnel: Breakthrough of the eastern Tube in Amsteg

At midday on June 16th, 2009 the tunnel boring machine Gabi 1 broke through the final metres of rock from Erstfeld to Amsteg in the eastern tube of the Gotthard Base Tunnel. It covered a 7.2 km long section in only 18 months thus arriving in Amsteg some 6 months earlier than scheduled. As a result Bundesrat Moritz Leuenberger was on the spot to congratulate the tunnellers on their terrific achievement.
On account of objections pertaining to the award of the contract to the Gotthard-Basis-tunnel Nord (AGN; Strabag AG Tunnelbau) joint venture, work started on December 4th, 2007 some 1½ years later at the Gotthard Base Tunnel’s north portal in Erstfeld with the starting up of the solid rock tunnel boring machine (Gripper TBM) Gabi 1 (S-229 Herrenknecht AG; 9.58 m diameter) and the excavation of the eastern tube towards the south. 18 months later and 6 months earlier than planned it arrived at the boundary limit in Amsteg after covering 7.2 km. The tunnel tube was broken through on June 16th, 2009 with great accuracy: the deviation from the desired axis equalled 4 mm horizontally and 8 mm vertically. The average rate of advance while excavating extremely tough rock and overburden of up to 1,000 m amounted to approx. 14 m. The peak daily rate attained almost 40 m of driven and secured tunnel tube.
The TBM Gabi 1 was previously applied in the tunnel section between Amsteg and Sedrun, where from October 2003 until June 2006 it drove 11.3 km of tunnel (max. 35 m/working day) attaining a 9-month edge over the construction programme. It was subsequently dismantled underground, transported out of the tunnel by rail and reassembled following a comprehensive inspection in front of the north portal at Erstfeld. It restarted heading towards Amsteg from that point in December 2007.
In the western tube the TBM Gabi 2 (S-230, Herrenknecht AG) had excavated 5,908 m or 83 % by mid-June 2009 so that some 1,240 m has still to be tackled until the section boundary with Amsteg is reached – with the breakthrough scheduled for autumn 2009. The 2 TBMs Gabi 1 and Gabi 2 are identical. The table contains details relating to the machines.
According to the AlpTransit Gotthard AG construction operations on the Gotthard Axis are making good progress. The penultimate breakthrough of the altogether 4 on the section between Erstfeld and Amsteg was celebrated in mid-June 2009. 133.9 km or 87 % of the total length of 153.5 km constituting the tunnel tubes, shafts and headings of the Gotthard Base Tunnel has been excavated. After mastering the Piora Basin in October 2008 and February 2009 the 2 TBMs are progressing well in the south tunnel section between Faido and Sedrun – with 6,644 m or 61 % having been driven in the eastern tube and 6,048 m or 53 % in the western one by the 2 identical TBMs (S-210 and S-211; Herrenknecht AG; 9.43 m diameter). The main breakthrough between Sedrun and Faido is scheduled to take place at the beginning of 2011 and the 57 km long Gotthard Base Tunnel is due to open in 2017 so that the world’s longest railway tunnel will then run through the Gotthard.

G. B.