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Switzerland opens world’s longest, deepest tunnel

The 57km-long, 2.3km-deep Gotthard rail link reflects 20 years of engineering and TBM operations

The first geologists to survey the route though it impossible to bore straight through the Gotthard.
The first geologists to survey the route though it impossible to bore straight through the Gotthard.

The 57-long, 2.5km deep Gotthard rail link through the Alps – the world’s longest, deepest tunnel – has opened in Switzerland after 20 years of tunnelling and construction at a cost more than $12bn.

The Gotthard base tunnel run on a flat low-level route –the first of its kind in the Alps – and bypasses the old rail line and tunnel, built in 1882 along a winding route up and through the mountain.

The project is about trade: the existing the old rail tunnel through the Alps is slow and cannot cope, and the Gotthard road tunnel, opened in 1980, now sees more than a million freight trucks a year.

The solution: twin 10m-diameter tunnels carved out by specialist tunnel-boring machines (TBM) that were able, on good days, to excavate 40m of tunnel a day – in a world record for the technology – and remove 28.2m tonnes of rock in the process.

The plans were stalled for a century because the first geologists to survey the route though it impossible to bore a tunnel straight through the Gotthard, because of the unpredictable rock.

Ultimately, the rock did indeed prove to “as soft as butter” in parts, forcing the TBMs to inch along at no more than half a metre a day, carefully exploring the space.

Also, as the world’s deepest tunnel, with 2.3km of mountain above it in places, the tunnel has had to be girded along its entire length with reinforced steel rings to prevent it collapsing in on itself.

In all, the project has cut not just two 57km-long tunnels, but 152km of passages and shafts.

Technology aside, the work has taken 17 years, 365 days a year, 24 hours a day, and more than 2,000 people have worked on the tunnel. There have also been accidents, with nine deaths.

But the route should now be much safer with the Gotthard’s twin tunnels transporting Europe’s freight with up to 260 trains a day travelling at 250kmph with no danger of collision.

The tunnel cuts 45 minutes off the journey time between Zurich and Lugano (to just under two hours), but also shortens so-called Rhine-Alp corridor from the ports of the Netherlands to Genoa in Italy.

Switzerland's transport minister, Doris Leuthard, is especially happy that her country, not in the EU, but in the heart of Europe, can contribute something so important to the European economy.

“We are a small country and we are landlocked, so we know co-operation is key, and this project of co-operation symbolises what Europe and Swiss engineers can do – and they did a fantastic job.”

At 57km, the Gotthard base tunnel is 3km longer than the world’s current record-holder, the Seikan rail tunnel that links Japan’s two largest islands, Honshu and Hokkaido.

However, the Chinese government now plans to build a tunnel underneath the Bohai straits measuring 123km – more than twice the length of the Gotthard base tunnel – to reduce journey times between the port cities of Dalian and Yantai from eight hours to 45 minutes.

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Construction Week - Issue 751
Oct 13, 2019