Miracle under the Alps

The Gotthard Base Tunnel will be the most important element of the new flat rail link through the Alps. It is ineresting to know that in total, an estimated 24 million tonnes of rock have been excavated – the equivalent of five times the volume of the Great Pyramid of Giza.

Technically, it is an absolutely unique project. The Swiss have set the bar so high that no one will easily be able to clear it.

But the project has not been without problems. Early during the drilling operation, for example, on March 31, 1996, drilling experts, assistants and a geologist were carrying out geologic tests. They 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. It is a miracle that none of the workers present were injured.

The Piora Mulde is a narrow, vertical band in the heart of the Alps made up of 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.

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. 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, if we take all the tunnels, including the cross tunnels, to be added together, they would extend for 153 kilometers. Up to 2,600 people worked on the project deep under the earth’s surface, battling with the dust, noise, humidity (влажность) and temperatures of 30 degrees Celsius.

In the drilling of the tunnels, workers relied on eight gigantic, 3,000-ton tunnel drilling machines simultaneously. 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.

But in zones where the rock was particularly brittle (ломкий), workers were forced to use more traditional methods, such as explosives. Workers were ultimately successful in stabilizing the unstable. But at the spot (место) where one of the emergency stops (аварийная остановка) was to be built, the Faido site, engineers discovered another area of instability. The large cavern (большая пещера) 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 in the same segment when, in July 2005, a tunnel boring machine (TBM), known as Gobi II, got stuck when it unexpectedly encountered a section of unstable, soft rock. The tunnel promptly collapsed in front of the TBM’s cutting head – and there is no such thing as reverse with a tunnel boring machine. Experts on the project found themselves with the unexpected task of trying to calculate the extent of the section of less stable rock, as well as having to rescue the TBM by digging it out of the place where it had got stuck – a process that would take several months.

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.

Дата добавления: 2015-10-31