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World’s longest and deepest tunnel opens

The world’s longest and deepest tunnel, the Gotthard Base Tunnel in Switzerland, has opened after 17 years of construction.

The 57km long, twin bore tunnel cuts through the Swiss Alps, linking the north portal at Erstfeld with the south portal at Bodio cutting journey times between the two locations.

Construction started in 1999 after a popular vote held in November 1998 secured the long-term funding for the New Rail Link through the Alps (NRLA). Finance for the 12.5bn Swiss Francs (£8.7bn) project has come from three sources: the heavy goods vehicle charge (HGVC, 60%), mineral oil tax (10%) and VAT (30%).

During the construction of the tunnel, the tunnellers had to bore through a wide variety of different rock strata, from hard granite to crumbly sedimentary rock. Tunnel boring machines (TBMs) carried out 80% of the work in the main tunnels and conventional blasting methods were used for the remaining 20%. In total 28.2M.t of excavated material was removed from the tunnel.

To save time and money, contractors worked on different sections of the tunnel at the same time. Workers, materials and machinery were transported to the construction sites in the mountain via access galleries and shafts.

The tunnel is also the world’s deepest tunnel, with rock cover up to 2.3km in depth and the temperature inside the mountain reaching as high as 50°C. The tunnel has virtually no gradients allowing trains to travel through it at up to 250km/h.

There have been four TBMs used on the project: Erstfeld and Amsteg were both 9.58m in diameter and 441m long; Faido was 9.43m in diameter and 450m long; and Bodio had a diameter of 8.83m and was 377m in length.

“This is a huge engineering achievement. The world’s longest train tunnel at 57km, and the machinery used to carve a passage through the mountain is a feat in itself – it is akin to a ‘moving factory’ half a kilometre in length. While cutting through the rock, the machine transfers the debris backwards and simultaneously places the pre-formed segments of concrete that form the shape of the tunnel,” said fellow of the Institution of Civil Engineers (ICE) and member of the British Tunneling Society Martin Knights.

“I’m pleased to see the vision finally come to life, and to see the project benefit from the major technical advances in tunnel boring machines made in the 1960s and 70s.”

The opening of the tunnel will allow passenger trains to travel more quickly through the Alps and reduce the number of locomotives needed by freight trains. It will also shorten the travelling distance between Altdorf and Bellinzona by 30km.

Facts and figures:

  • 4M.m3 of concrete has been used on the project
  • 125,000t steel rings
  • 4,800km rock anchors
  • 16,000t reinforcement
  • During peak periods, around 2,400 people were working on the tunnel construction around the clock in three shifts
  • For the two main tunnels and the safety, ventilation and cross cuts, a total of 152km of tunnel has been bored
  • As many as 260 freight trains will be able to pass through the Gotthard Base Tunnel every day.


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