This month our engineering showcase is the recently completed Gotthard Base Tunnel. A 57 km railway base tunnel that stretches through the iconic Swiss Alps, recently open after 17 years of construction. It’s the world’s longest traffic tunnel and the Swiss say it will revolutionise European freight transport. It differentiates itself from the old winding Gotthardbahn rail tunnel as it’s a flat low level route, the first of its kind through the Alps.
Traffic through the St Gotthard Pass and tunnels had increased more than tenfold since the 1980’s and existing tunnels were at full capacity by the turn of the millennium. This was largely due to ever increasing traffic from transport trucks. In 1994 the Alpine Protection Act was created, aiming to shift as much weight as possible from truck to train transport. The main aim of this was to increase local transport capacity through the alpine barrier, and the shift of truck to train would also reduce environmental damage to the area.
The construction of the project started in 1993, with the eventual launch in June 2016.
The work was carried out by AlpTransit Gotthard AG who are a subsidiary of the Swiss Federal Railways.
Four access tunnels were created so that construction could be carried out simultaneously at 4 different sites, this cut construction time in half. These tunnels were named Ersfeld, Amsteg, Sedrun and Faido and a fifth called Bodio was added at a later date. There were two stations created at Sedrun and Faido and these now serve as emergency stops and evacuation routes.
At first surveyors were concerned that It may be impossible to bore a tunnel because of the unpredictable density of the rock, which varied from solid granite to soft buttery rock types. This meant that excavation in the softer areas was reduced to a snail’s pace.
Engineers had to deconstruct and blast through over 73 different kinds of rock in order to manufacture the tunnel, which travels as deep as 2.3km below the surface of the mountains. Rock temperatures can reach 46C at that kind of depth. In total, more than 28 million tons of rock was excavated which was then broken down into concrete that was used to help build the tunnel.
Another problem faced was the sheer force of gravity that comes with being 1.4 miles beneath a mountain. Reinforced rings had to be inserted to prevent it collapsing in on itself.
The East tube broke through during October 2010 and the West tube eventually followed in March 2011. Test phases then commenced across the 8-mile stretch between Faido and Bodio. 2,000 people worked on the tunnel in total and unfortunately 9 workers died during the construction. These workers are now commemorated by a plaque on the northern end of the tunnel.
The project cost a staggering £8.3 billion to build over a 17-year period but sixty-five per cent of the construction costs were funded by taxing heavy duty vehicles. Over 3,000 heavy duty vehicles used the old tunnel daily and 180 freight trains. About 260 freight trains and 65 passenger trains will pass through the new Gotthard tunnel each day and it will cut 45 minutes off the journey time between Zurich and Lugano.
The Gotthard Tunnel is a true engineering feat and The Swiss Museum of Transport is hosting a special exhibition around the project until October 23rd which we would highly recommend a visit to if you are in the area.
By Ingenieurlösungen (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons