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The 3.2-kilometer-long Belchen Tunnel, between Basel and Egerkingen, crosses the Jura Mountains. A characteristic feature of this mountain range is the large proportion of gypsum Keuper, which caused damage to the tunnel's supporting structure through swelling. It was necessary to renovate the two existing double-track tunnels from the 1970s. For this purpose, a third tunnel, the so-called renovation tunnel, is being built. The #tunnel boring machine from #Herrenknecht and #MartiTechnik is special because it excavates the tunnel over its 75-meter length, fills it with segments, seals it and finally concretes it. The diameter of the boring head is almost 14 meters.