Less than 10m now separates the long headings into the Gotthard Massive from Erstfeld in the north to Bodio in the south. History will be made next Friday (15 October) when the first Bodio-Faido TBM breaks through into the drill+blast heading from Sedrun to finish 57km of rail tunnel through the base of the Swiss Alps.

Progress of excavation and concurrent lining procresses

Swiss politicians and dignitaries, project directors and contract managers as well as senior managers of the leading suppliers and the workers themselves will gather for an official breakthrough on Friday afternoon when the TBM will be fired up at 2pm to cut the last 1.5m and mark this truly momentous feat of civil engineering and endurance.

The crews of the TBMs and drill+blast headings have truly blazed a trail. This last breakthrough occurs nearly 2,000m below the top of the Alps and more than 8km from the nearest exit through the 700m deep shaft at Sedrun and more than 13km from the access adit at Faido.

On a project of this magnitude - the longest, largest, most ambitious and technically demanding rail tunnelling projects of this age - there have been serious set backs as crews have tunnelled into the unknown. Extreme geological conditions buried a TBM heading from the Amsteg adit for more than six months and had another from the Faido heading at a standstill for five months from March to July this year.

These and other challenges, some not related to the excavation work, have cause a time slip of some 10 years from the original programme timeline. The original plan set in 1998 was to have the baseline railway open in 2007. As it is, TBM excavation of the longest drives for the main tunnels started from the Bodio portals in 2001 with drill+blast work starting from the base of the deep access shaft at Sedrun in 2002. Work on the shorter TBM drives from the northern Erstfeld portals started in 2006. The project is now scheduled to open at the end of 2017.

The last of the four Herrenknecht TBMs that have excavated much of the total underground excavation is working and the very last breakthrough for the entire project in April next year 2011. That will repeat the celebrations to be had next Friday with even greater enthusiasm and adulation.

References

Breakthrough milestone for Gotthard Base Tunnel - TunnelTalk, September 2009
Gotthard TBM safely across the Piora Mulda - TunnelTalk, Nov 2008
Bodio tunnel lining wurms - Switzerland - TunnelTalk, Dec 2004

AlpTransit Gotthard AG

Safe breakthrough reward for the TBM crews

Celebrations on Wednesday, September 16, shortly before 4pm, marked a significant achievement for the mammoth Gotthard Baseline railway tunnel project. Breakthrough of Gabi 2, the 9.58m diameter Herrenknecht gripper TBM, confirmed 91%, or about 137km of the total 151.8km of excavation needed to provide a rail connection through the base of the Gotthard Massive, portal to portal, is now complete.

The Gabi 2 rock TBM completed its 7.2km western tube drive from Erstfeld to Amsteg in 18 months to reach its target some six months ahead of schedule. Its sister machine, Gabi 1, achieved the same performance in the eastern tube when it broke through at Amsteg in June.

The average daily tunnelling performance for the two Herrenknecht TBMs through hard rock and mountain overburdens of up to 1,000m, was approximately 18m/day. The best daily performance by Gabi 2 was 56m of near 10m diameter tunnel excavated and secured in a 24h production day. This is being claimed as a world record for a boring machine of such dimensions. The alignment axis for Gabi 2 at breakthrough deviated from spot on by a tiny 4mm horizontally and 8mm vertically.

This final TBM breakthrough marks the end of all excavation work in the world's longest railway tunnel on the northern side of the Gotthard Range. The two Herrenknecht machines working in the southern section of the twin tunnel project from the Bodio portal and the Faido intermediate adit are expected to achieve the final breakthroughs into the drill+blast headings of the central Sedrun section at the end of 2010/early 2011.

Renzo Simoni, Chairman of AlpTransit Gotthard AG, the client of this modern day pioneering project, is said to be satisfied with the performances achieved during the construction of the Gotthard Base Tunnel. Following completion of the tunnel excavations, work progresses with casting the inner concrete linings and installation of all the necessary M&E services. Commercial operation of scheduled train services remains scheduled to start at the end of 2017.

References

Great celebrations for Gotthard TBM arrival - TunnelTalk, July 2009
Gotthard TBM safely across the Piora Mulda - TunnelTalk, Nov 2008
Bodio tunnel lining wurms - Switzerland - TunnelTalk, Dec 2004
AlpTransit Gotthard AG