Karavanke tunnel: Lessons learned during tunneling in extremely squeezing ground conditions

Abstract The Karavanke tunnel is a double tube double lane motorway tunnel connecting Slovenia and Austria through the Karavanke massif with overburden up to 1100 m. On the Slovenian side, the tunnel runs through very diverse ground conditions, considering a 1 km long section in soft and highly deformable Permo‐Carboniferous claystones, siltstones, and sandstones (PC) under high overburden as the major challenge. Construction of both tunnel tubes in PC, the Western tube in 80 s and the Eastern tube recently, was characterized with large deformations up to 1.6 m and heavy damage of the primary lining requiring an extensive remediation of the initially installed lining, sometimes even several times. This article focuses solely on the Permo‐Carboniferous section and presents the construction of the Western tube, application of the lessons learned into the design of the Eastern tube, performance of the designed primary lining in the Eastern tube, development and application of an alternative excavation and support concept to cope with the extreme deformations, and remediation of the primary lining using solely fiber reinforced shotcrete (fibercrete).