The Gotthard Base Tunnel: Miracle Under the Alps
After years of work deep under the surface of the earth, drilling on the Gotthard Base Tunnel is set to be completed on Friday. It will be years before the first trains roll through the 57-kilometer-long tunnel, but given the difficulties workers have encountered, it is a wonder they have come this far.
They are both celebrated as wonders of mankind's ingenuity and engineering expertise: the Panama Canal and the Suez Canal, deep pathways slicing through the surface of the earth for the benefit of global trade.
On Friday, a third such wonder will take a decisive step toward completion. Only 1.8 meters (just under six feet) of rock stand in the way of the Gotthard Base Tunnel from becoming the longest tunnel in the world. On Friday afternoon, the gigantic drilling machine Sissi is scheduled to break through that final barrier far below the peaks of the Alps. Accompanied by a subterranean celebration and live coverage from the world's media, the breakthrough is a significant milepost on the road to completion for Europe's largest infrastructure project.
"Technically, it is an absolutely eye-popping project," Kurosch Thuro, a tunnel construction expert from the Munich Technical University, told SPIEGEL ONLINE. His colleague Markus Thewes from the Ruhr University in Bochum says "the Swiss have set the bar so high that no one will easily be able to clear it."
The undertaking has not been without problems. Early on in the drilling, for example, on March 31, 1996, drilling experts, assistants and a geologist were carrying out geologic tests when they suddenly struck a layer known as the Piora Mulde. Suddenly, a huge quantity of water and sand shot out of the drill shaft with unimaginable force.
The Piora Mulde is a narrow, vertical band in the heart of the Alps made up of finely ground Dolomite -- a white, often crystalline mineral, sediment which settled on the bottom of a sea 230 million years ago. Mixed with water, the substance becomes unpredictable -- and presented a difficult challenge for the tunnel engineers to overcome. On that day in March over 10 years ago, thousands of cubic meters of the stuff flooded into the drill shaft. It is a miracle that none of the workers present were injured.
The Piora Mulde was just one of some 90 geological problem zones that had to be overcome during the drilling of the 57-kilometer-long tunnel. "It was not without danger," confirms Thuro.
It won't be until 2016 or 2017 before the first trains can roll through the tunnel on their way between Zurich and Milan. The digging, however, despite all the difficulties and delays, will be brought to a successful conclusion on Friday.
Workers removed fully 23 million tons of rock in the drilling of the tunnel -- actually a pair of tunnels, each 10 meters in diameter. Indeed, were all the tunnels, including the cross tunnels, to be added together, they would extend for 153 kilometers. Up to 2,600 people worked concurrently on the project deep under the earth's surface, battling with the dust, noise, humidity and temperatures of 30 degrees Celsius (almost 90 degrees Fahrenheit).
Forced to Use Explosives
And there were plenty of dangers. Eight workers have lost their lives so far in the construction of the Gotthard Base Tunnel. During the construction of the old Gotthard Tunnel in the 19th century, the total was close to 300.
In the drilling of the tunnels, workers relied on eight gigantic, 3,000-ton tunnel drilling machines simultaneously. "An exceptional logistical plan" was necessary, says Thewes. An 800-meter-long shaft was drilled vertically into the mountain, for example, so that workers could begin working in the middle of the tunnel.
Often, though, the outsized drilling machines provided little help. In zones where the rock was particularly brittle, workers were forced to use more traditional methods, such as explosives. Zones of stone that had been crushed to bits as the Alps formed proved to be particularly problematic.
"Nobody has ever worked in such material at such a depth," says geo-technician Georgios Anagnostou, from the Swiss Federal Institute of Technology in Zurich. In such areas, tunnel engineers were forced into something of a gamble. They allowed for softer material to push into the tunnel and installed thick tubes in those segments. Computer models had forecast distortions of up to one meter. In the end, the deformations were around 80 centimeters.
Not the Only Problem
Workers were ultimately successful in stabilizing the unstable. "There are no longer any parts of the tunnel where there are any distortions worth mentioning," says Anagnostou.
But other problems awaited. At the spot where one of the emergency stops was to be built, the Faido site, engineers discovered another area of instability. The large cavern that was to house the subterranean emergency station had to be built elsewhere, and is now 300 meters further to the south.
Another problem arose when, in the same segment, one of the drilling machines got stuck and was virtually buried by debris falling from the tunnel roof. Time was lost as workers had to grind up and remove the stone that had filled the tunnel -- the roof was then stabilized using steel and concrete. Similar incidents occurred in several other parts of the tunnel. At one point, one of the drilling machines was unusable for a full six months -- while just 40 meters away in the parallel tunnel, workers encountered no trouble at all.
Indeed, in the end the Piora Mulde zone proved unproblematic. The real tunnel was drilled a few hundred meters below where the test tunnel had been flooded -- through a stable area of marble. "The marble was the best material that workers encountered in drilling the Gotthard Base Tunnel," says Anagnostou. "They didn't take risks. They did their research first."
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