Gotthard Base Tunnel, The World’s Longest Tunnel

Author: Arvind Padmanabhan

Engineering challenges and achievements


The world’s longest tunnel at 57.1 km was opened in Switzerland two days ago and the event was celebrated at the swissnex India in Bangalore last evening. The tunnel is a feat of engineering, taking 17 years to complete. It connects the north and south of Europe by cutting through the Alps. Known as the Gotthard Base Tunnel, it starts at Erstfeld in the North and ends at Bodio in the South.

This is by no means the first tunnel to go through the Alps. In the 13th century, a bridge was built in the Gotthard pass. Over the centuries this evolved to a road but a proper road tunnel was not made till 1708. That tunnel was only 65 meters long. A subsequent road tunnel was built in 1980. A 15 km rail tunnel came a century earlier in 1882 and it is still in use. This tunnel sits at an altitude of 1150 m above sea level whereas the Gotthard Base Tunnel is at 550 m above sea level. It shortens journey times, allows more trains to go through every day and allows heavier freight trains to go through.

We were fortunate to have with us Prof. Christian Schlüchter from the Universty of Bern to explain many of the challenges that the team faced during the construction of the tunnel. Prof. Schlüchter has been involved with the project from its early days and gave a passionate talk about his involvement. He set the tone for the evening by welcoming us as “tunnel lovers.”

Engineering may appear to many as a dirty job, fixing things and replacing parts soaked in oil and grease. But engineering is also about creating something that can be beautiful. The professor often remarked how beautiful the tunnel looked in its elemental form before the cabling, tracks and systems were fitted inside it. A mountain is a formidable barrier and to cut through it and make something beautiful is indeed an achievement to be proud of.

Why is something beautiful? Take the example of the Millau Viaduct in Southern France, which opened in 2004. Is it beautiful because of the landscape in which it stands? Is it beautiful because it towers above the valley? Is it beautiful because of an obvious contrast between nature and a man-made construction that suggests modernity and progress? Perhaps, it’s a bit of everything. But how do you judge the beauty of a tunnel? This is where the geologist/engineer speaks.

Sometimes beauty lies more in the journey than in the destination. When an engineer looks at a completed project, he brings with it memories of the journey. He recalls the tough decisions that were taken. He knows what worked and what didn’t. To an engineer, the process of creation is deeply linked to knowledge and satisfaction. So when engineers say something is beautiful, others have to try to see it from their perspective of what went behind the scenes. It’s exactly this that Prof. Schlüchter presented to us last evening and made the audience appreciate the tunnel even more.

One innovation that was done during this construction was the engineering of barrel-shaped metal structures that kept the tunnel from collapsing inwards once the earth had been excavated. Under the immense weight of the rock above, the metal bars would push against one another. The professor described this as “music” from the creaking of metal and the crushing movement of jostling rock. One gets the picture of man trying to tame nature, man trying to bring order out of chaos and entropy.

While the length of the tunnel is something to be noted for its record, the greater challenge was the depth from the surface. At its deepest, the tunnel is 2.3 km from the surface. This in itself was a challenge because the geology of the mountain from the surface to that depth was not all that clear. At times, exploratory tunnels had to be dug to study the geology. Simulations were done to forecast tunnel temperature at various points. In one case, the forecast was higher than the actual temperature. It turned out that water percolating in the rock above actually lower the temperature. In general, the rock structure was largely crystalline and this simplified the construction.

One notable achievement was the alignment when the north and the south parts of the tunnel finally met. The alignment was off by only 8 cm horizontally and 1 cm vertically. This was done with the help of precision lasers. Likewise, every piece of equipment installed in the tunnel for the eventual operations had to be highly reliable. This includes the ventilation systems, sensors, the power supply, emergency systems, the cabling, the electronics, the signalling systems, and so on. Engineers from Alstrom and ABB were present at the event to share their involvement in the project.

During the Q&A session, the professor noted two main challenges: the actual decision to go ahead with the project and the fact no one knew the exact geology of the mountain. But once the decision was made, it was really a matter of believing that the project could be completed and pulling together all necessary expertise to get the job done.

I will end this post with some factual information that might interest the readers:

  • Length: 57.1 km
  • Deepest point: 2.3 km below surface
  • Altitude: 550 m
  • Tunnel length excavated: 152 km
  • Excavated earth: 28.2 million tonnes
  • Excavation method: 20% conventional blasting + 80% tunnel boring
  • Capacity: 260 freight trains/day + 65 passenger trains/day
  • Maximum speed: 160 km/h for freight trains and 250 km/h for passenger trains
  • Travel time: 20 minutes
  • Construction time: 17 years
  • Total cost: 23.5 billion CHF
  • Signalling: GSM-R (GSM for Railways)
  • Ventilation system power consumption: 50.6 MW

Author: Arvind Padmanabhan

Arvind Padmanabhan

Arvind Padmanabhan graduated from the National University of Singapore with a master’s degree in electrical engineering. With more than fifteen years of experience, he has worked extensively on various wireless technologies including DECT, WCDMA, HSPA, WiMAX and LTE. He is passionate about tech blogging, training and supporting early stage Indian start-ups. He is a founder member of two non-profit community platforms: IEDF and Devopedia. In 2013, he published a book on the history of digital technology:

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