The construction of Norway's longest railway tunnel marked a breakthrough for the use of tunnel boring machines in hard rock tunnelling. In Scandinavia long rail tunnels have hitherto been drilled and blasted rather than bored. In the Follo Line Project, the tunnel boring machines made a convincing case for themselves all the way through the extremely hard Norwegian rock. Four tunnel boring machines (TBMs) by Herrenknecht worked simultaneously to excavate the main part of two 20-kilometer railwa
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