The Follo Line project in Oslo is a technology revolution for tunnel-rich Norway. Previously, tunnels over there have usually been driven with explosives. But for the largest infrastructure project in the land of the fjords, tunnel boring machines are now being used. Since late 2016, four Double Shields from Herrenknecht have been simultaneously drilling through the tough hard rock. A first worldwide and a logistical challenge: in the extremely hard gneiss, the disc cutters wear out faster, requiring up to 4,250 cutter changes per machine in the course of the project. The worn out disc cutters are taken to Schwanau, 1,500 kilometers away, where they are completely refurbished for reuse.

The drives have performed better than planned: by March of 2018, 24 of around 37 kilometers of tunnel had already been built. From the end of 2021, high-speed trains will travel through the two new tubes at up to 250 kilometers per hour. The journey time between Oslo and Ski, about 20 kilometers to the south, will be halved from 22 to 11 minutes. For the Norwegian capital with its 600,000 inhabitants and the region around Ski, which expects population growth of 30 percent by 2025, the Follo Line is a lifeline for the new area.