SBT Tunnelling and exploration measures in swelling and surging rock

The article describes excavation and investigation measures for the Semmering Base Tunnel that became necessary due to the occurrence of swelling rock mass, particularly anhydrite. The swelling behaviour was primarily governed by the specific surface area of the anhydrite and its structural characteristics. Massive, scarcely jointed anhydrite exhibits low swelling potential, whereas fractured zones pose significantly higher risks. Extensive investigations during excavation, geological documentation, and laboratory analyses enabled a detailed assessment of the geological conditions. Based on these findings, the typical cross‐sections — especially the geometry of the base — as well as support measures to resist swelling pressures were defined. These measures include avoiding water ingress, applying sealing grouting to reduce the water flow into the tunnel, and designing the inner and outer linings to allow for time‐dependent swelling pressures. The complex geological structures resulted in uncertainties and required situational adjustments of the support systems during tunnelling. Overall, the article demonstrates that a flexible, geologically informed approach and close coordination between geology, tunnel design, and construction are essential to effectively manage the risks associated with anhydrite‐bearing ground.