© AlpTransit Gotthard AG/Angel Sanchez

As Heidi Drills Her Way ...

... through the mountain Jürgen Mielenz experiences some of the most exciting and intense moments of his working life. When it comes to the Gotthard Tunnel, Mielenz has his own particular type of tunnel vision. He sees himself standing in the rock cave illuminated by fluorescent lamps, the soil rough underfoot, looking up to the roof that was blasted free 15 meters above, and thinks: There are another 2,000 meters of rock on top of it. It’s hard to imagine.

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When people carve a way through a mountain, they make history. And the Gotthard Base Tunnel, which leads from Germany to Italy, tells a special story. At 57 kilometers, it is the longest railway tunnel in the world. Mielenz (left) is one of the pioneers who completed the mega-project that was opened in 2016. HOCHTIEF spent eight years working on the shell. Mielenz is in charge of the engineering office. This is where the areas of technology and preparatory work on the construction site come together. The advance in the tunnel is measured.

Exciting: There is a certain amount of uncertainty in the beginning. How are we going to get through? At least he is not alone. There are up to 1,000 employees working underground. And then there is “Heidi,” for example. “It’s an appropriate name for a project in Switzerland,” Mielenz thinks. Heidi is one of the two giant tunnel boring machines. She is 450 meters long and weighs 2,700 metric tons. The term “behemoth” must have been coined to describe this kind of machine. And Heidi has teeth, 58 of them to be exact. She has a circular “set of teeth” that measures nine meters from one end to the other. Heidi makes a screeching sound as she drills her way further and further into the mountain. She advances by roughly twelve meters every day. “Tunnelers want to make progress,” says Mielenz. It’s hot work. This deep in the mountain, the thermometer measures a temperature of almost 50 degrees Celsius. They have built a type of air-conditioning system with water pipes, bringing the temperature down to 30 degrees – almost cool. Cool enough to work.


  • The construction of the tunnel took a total of 17 years
  • HOCHTIEF used 1.5 million cubic meters of concrete in the tubes
  • A total of 28.2 million metric tons of rock were excavated from the tunnel
  • The material excavated from the tunnel would fill 4 Great Pyramids of Giza

Intense:  For Jürgen Mielenz, it is a dream come true. “The Gotthard Tunnel is the project of my life. Being involved in building something like that is every engineer’s dream."

Many tasks are performed simultaneously: Excavation, securing, interior work and also the crosscuts must take place after tunneling. The excavated rock is transported out of the tunnel on debris trains, while concrete is brought in. Up to 80 engines are in use simultaneously during tunnel operation. It’s pure logistics. “It’s hard to get your head around the magnitude of these amounts,” says Mielenz with great enthusiasm. “You could build four Great Pyramids of Giza with all the excavated material.” At the breakthrough of the tunnel in 2010, the north and south tubes connected exactly as planned – it was precision work.

Legend: For Jürgen Mielenz, the Gotthard Tunnel is a real legend. He still loves the T-shirt he wore on the day of the breakthrough. It says, in large letters across the chest: “World Record at Gotthard. 57 Kilometers.”

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