Construction Challenges of the Karavanke Tunnel’s Eastern Tube in Water-Bearing Conditions

Summary

Abstract

The construction of the new eastern tube of Karavanke Tunnel will be fully completed in 2026. Tunnel excavation, finalized in 2024, was executed under highly heterogeneous geotechnical and hydrogeological conditions, including several sections affected by active aquifer zones. The initial segment advanced through the Werfen Formation, where the transition from clastic units to carbonate rocks and the crossing of a localized fault zone resulted in a approximately 100-m section with substantial groundwater inflows, reaching rates of up to 35 L/s. This zone is additionally characterized by the presence of anhydrite, which exhibits pronounced swelling behavior when exposed to water. Such deformation processes had previously been identified in the existing tunnel tube and were further confirmed through geotechnical monitoring in the newly constructed eastern tube. Another critical zone was encountered during the transition from the Werfen Formation into the Schlern Dolomite and subsequently across the Goliški Fault, where tunnelling intersected a broader mylonitized dolomite zone approximately 10 m in thickness. In both major hydrogeological zones, targeted pre-drainage measures were implemented to mitigate inflows, enabling safe excavation progress and providing essential data for characterizing the groundwater regime. The improved understanding of the hydrogeological conditions was subsequently employed to refine the alignment and design parameters of the planned underground water-collection system, intended for the capture and distribution of high-quality groundwater resources.