In just a few months, the first high-speed trains will zip through the brand new Gotthard Base Tunnel, which has been dug deep beneath the Swiss Alps. It will be the world’s longest and deepest railway tunnel, but will it also be the safest?
As they rush to catch their trains, few travellers notice the memorial next to Switzerland’s Airolo railway station. It honours the 200 or so ‘martyrs of labour’ who died building the first Gotthard Rail Tunnel. Back when it finally opened in 1882 - after a long and troubled decade of construction - it was the world’s longest such tunnel. Fast-forward to October 2010 and a sea of workers in their orange and white construction helmets cheered as the huge drilling machine broke through the final barrier of rock to complete the new Gotthard Base Tunnel. Swiss voters had approved the project in a 1992 referendum, in the hope that it would speed up journey times and reduce accidents, fatalities and environmental damage by shifting both freight and passengers from mountain roads to deep beneath the ground.
The cost was astronomical - 9.8 billion Swiss francs, or $10.3bn - but voters agreed that it was worth it, not least as the new route will cut journey times from Lucerne to Bellinzona (Switzerland’s gateway to Italy) by nearly an hour and a half.
Safely building a record-breaker
“Before starting, there were a lot of so-called experts, many of them geologists, who said that it would be impossible, or that it would take 50 years to do,” says Renzo Simoni, head of AlpTransit Gotthard Ltd, the company in charge of the tunnel’s construction. “But they were wrong.”
Construction started in 1996. Yes, it took 20 years to complete, but construction has been remarkably smooth for such a record-setting project. Burrowed 2,300m beneath the Swiss Alps, its full length is 57km, with a total of 151.84km of tunnels, shafts and passages. Once it opens to the public in June 2016, passengers will be able to hop on a train travelling at more than 240km/h, and get from Zürich to Milan in just two hours and 50 minutes, a saving of about an hour on the current travel time.
So how do you go about drilling a pair of train-sized tunnels though the depths of Europe’s biggest mountain range?
Advance preparation was key to ensuring success and safety inside the mountain. First, the team was able to gather a huge amount of data from previous projects and exploration in the region. This part of the Alps is already home to the first Gotthard Rail Tunnel, plus the Gotthard Road Tunnel and a number of hydropower schemes. The mountains are also criss-crossed by unused, defensive tunnels built by the Swiss army during the Second World War. All this gave the builders of the new tunnel a lot of insight into the region’s complex geology.
The team also undertook many investigative borings. In one instance, they excavated a 6,000m tunnel to explore what was expected to be a particularly difficult zone. From the end of this tunnel, further borings as long as 1000m were made, all the way down to the level of the base gallery. This exploration alone cost more than €100m, but provided the knowledge needed to develop the final design of the tunnel.
“Of course there were still some surprises,” admits Simoni. “One particular problem was that there was a zone of ‘squeezing rock’, where the hole tries to close again. Here, we had to deal with radial deformations of up to 90cm.”
The softer rock threatened to deform the tunnel, so engineers had to develop a new concept for tunnel engineering - flexible steel ribs that were anchored into the tunnel walls and then lined with concrete to absorb the rock pressure and protect the integrity of the tunnel. It was the first time so-called tunnel-lining machines were used in railway tunnel construction.
Then there were the two occasions when the 10m-wide tunnel boring machines became locked due to rock pressure. Each time it took up to five months of painstaking work to get the machines moving again.
Extreme working conditions
Some 2,600 people worked on the excavation at any one time, labouring in blisteringly hot, humid, noisy and dusty conditions, and surrounded by geological ‘problem zones’. In the deepest parts of the tunnel, 2,500m of mountain lies above the shaft, putting the rock around the tunnel and any water within it under extremely high pressure. That kind of burden results in temperatures as high as 45°C. “No one can work at that kind of temperature,” says Simoni. “We needed to install strong air circulation to bring the fresh air in and drive the hot air out. It’s one of the world’s most powerful ventilation systems.”
An on-site occupational health team constantly patrolled the tunnel, checking protective clothing and equipment, monitoring changes in temperature and humidity, ensuring miners drank enough water, and administering first-aid.
Back in 1996, it was a miracle that no one was injured when exploration works hit a watery layer of dolomite near the foundations of the Nalps Dam. Water spewed into the drill shaft - a phenomenon that caused many of the 200 fatalities during the 1870s construction. Stemming the flow took over 100 days and involved drilling holes into the rock and pumping in hundreds of tonnes of grouting mixture.
Although construction of the Base Tunnel has been far safer than its predecessor, the process has not been without tragedy: overall, eight workers have lost their lives. But Simoni is careful to note that none of these incidents were related to hazards specific to the project - rock fall, blasting, fire or toxic gases - but rather came from hazards found on any construction site. “This is an indication that the safety inside the tunnel has been very high,” he says. “Sadly, the result is the same: a death is a death.”
Delivering a danger-free ride
In June 2016, constructor AlpTransit will hand over the tunnel to Swiss Federal Railways, which plans to do a further six months of testing, before the tunnel route appears in official timetables. By December 2016, the tunnel’s safety features will have been tested 3,000 times to ensure a ride without danger.
Switzerland knows all too well how dangerous tunnel incidents can be. The nearby Gotthard Road Tunnel has proven to be relatively safe, not least given the sheer volume of traffic traversing its length. But everyone is desperate to avoid incidents or tragedies such as the 2001 lorry collision which fuelled a fire that killed 11 people, or the funicular tunnel fire that claimed the lives of 155 skiers and snowboarders across the border in Austria back in 2000.
This is why the operators are currently building maintenance and intervention centres in Erstfield and Biasca to house the specialist firefighting and rescue trains and facilities that would be needed in the event of an incident inside the tunnel. “The newest safety systems are installed inside the Gotthard Tunnel,” says Swiss Federal Railways spokesman Reto Schärli. “The European Train Control System (ETCS) Level 2 allows the trains to follow each other every two or three minutes.”
This system provides train drivers with data directly to their cabs, giving them detailed information about permission to proceed, correct routes, speeds and the status of the track, all of which is constantly monitored by a control centre. This removes the requirements for the majority of traditional - but less reliable - lineside signalling.
Two emergency stations at Faido and Sedrun will allow trains to cross over from one tunnel to the other in an emergency. In the event of a fire, ventilation equipment will suck smoke out of the tunnel and blast in fresh air through side tunnels and galleries.
A slight overpressure will prevent smoke from filtering into the escape route passages. If a train grinds to a halt before reaching one of the emergency stop stations, passengers can still escape the tunnel quickly and easily. Swiss Federal Railways are currently planning several rescue exercises to be carried out between November 2015 and March 2016. “Two single track tunnels have been built, with escape routes to a connecting gallery every 325m,” says Schärli. “During an emergency, passengers will be able to get through these galleries on to the safe side without having to cross the tracks or use lifts.”
The green sliding doors which form these emergency exits are a feat of engineering in themselves. Their doors are strong enough to stop fire and smoke, withstand 10-tonne waves of air pressure caused by the movement of trains, function without electricity, and yet remain simple enough to be opened by a child.
“A tunnel is only built after the breakthrough,” said then Transport Minister Moritz Leuenberger, shortly before the excavation was completed.
He is, of course, right. The construction of the Gotthard Base Tunnel has set a new precedent for this kind of civil engineering project, in terms of both its sheer achievements and the safety with which it has been completed. Let’s hope that it will not only prove to be the longest and deepest railway tunnel in the world, but also the safest.