Into the high-risk zone


Peter Guntli (with the white helmet) leads geology students through his section of the tunnel.

On 1 June 2016, the Gotthard Base Tunnel opened after just under 20 years of building work. Peter Guntli was involved in the construction of what is the world’s longest railway tunnel, working as chief geologist of the Sedrun section. He looks back on the project for us.

(From "Horizons" no. 109 June 2016)​​​

My daughter was four years old when she asked my sister: 'When will Daddy be finished with the tunnel?' She answered: 'When you get your driving licence'. So in this sense, we finished earlier than we expected back then. My daughter is 23 years old today and she still doesn't have her driving licence. But the tunnel will open on 1 June this year. For a long time I was unable to contemplate that this day would actually arrive. But now it's here. After working for 20 years on this project!

I came to the Gotthard Tunnel by chance, really. At the beginning, I had absolutely no experience. In a normal geology degree course, you don't learn how to build shafts or tunnels. We Swiss just stood in front of the huge black hole that was the Sedrun shaft, and we looked down and marvelled at what the South African shaft builders were doing down there. Over the years I acquired experience in tunnel building. I took courses, but most of it was learning by doing. And so I became the head geologist of the Sedrun section of the Tunnel.

Building a tunnel with gut feeling

Our main task is to assess the rock in front of us so that we can advise the engineers and tunnel constructors as they advance: are they going to be confronted with an unproblematic zone made of hard gneiss, where they can make progress without undue danger? And will they be able to secure the tunnel with just five centimetres of sprayed concrete and a few braces? Or is it going to be a high-risk zone with soft, squeezing rock and a heavy water flow where they will have to carry out advance drilling and institute comprehensive sealing and support measures?

You usually don't have much time to make elaborate tests in a laboratory. It's just not possible to stop construction for several days at a time. There are objective criteria that have been catalogued systematically and in detail. But in the end, you're left with your gut feeling. Or, to put it in more professional language, it's down to your experience and good teamwork. Luckily, nothing serious happened in my section in terms of the geology. But the 'normal' accident risk is still high on such a construction site. If a tool falls 800 metres down a vertical shaft despite all safety measures, it's best not to be standing under it. At the beginning in particular, I had a lot of respect for the tunnel – more than respect. Even if you get used to the atmosphere over time, it remains something special. It's not suited to everyone. It's odd to feel that there are thousands of metres of rock above you, not to mention the many kilometres you have to travel in the dark, the constant artificial light and the noise of the hammer drills. In the tunnel you have to work meticulously and carefully. It's not a place for fooling around. Though on one occasion my young colleagues did allow themselves an April Fool's joke: they wrote in the official survey report that they'd struck gold and were shutting the tunnel down over Easter in order to go prospecting. One of the people higher up who read it actually got angry and informed us that the gold belonged to the building contractors, not to the geologists!

Always on call

But as a rule, we're very serious about the job. We recently had a really strenuous day at the site, in a zone where there are many water-carrying layers that we had to investigate by drilling into them. We commissioned a specialised company to enter there with borehole cameras – and the water flow was ten litres per second. That wasn't easy. But we got a grip on the problem in the end. I was able to go home towards midnight.

I still enjoy my work. The tunnel is fascinating – but tiring. Basically, I've spent the last two decades on constant call, because we're building round the clock. On 1 June I will be very happy and very proud, but also very relieved..


As told to Christian Weber.