The 27.3 km long Semmering Base Tunnel with deep access shafts will be the third longest railway tunnel of Austria. The overburden depth is between 40 m and 800 m. The tunnel construction is divided into three lots. From the view of design and geotechnics, the project has many challenges. Overall more than 40 ground types were defined. The tunnel runs through many fault zones. Measures against squeezing, swelling and flowing ground have been designed. The carbonate rocks are partly karstified with a large groundwater reservoir. Extensive pregrouting works from up to 300 m long horizontal directional drillings are foreseen in order to reduce the predicted entering groundwater volume from up to 300 l/s and to protect the groundwater reservoirs. In accordance with the Austrian guideline for conventional tunnelling, a detailed geotechnical design was carried out.
The Semmering Base Tunnel (SBT) is situated in Eastern Austria and is part of the Baltic-Adriatic Corridor, which is one of the most important cross-Alpine lines in Europe. Based on extensive geological investigation in the station and alignment selection procedure and environmental impact assessment a detailed tender design was possible (Gobiet & Nipitsch 2015). Therefore, the driving method could be selected and furthermore various important technical, geotechnical, structural and environmental measures could be taken into account on time (Ekici et al. 2011). The tunnel is about 27.3 km long and is being driven from the portal at Gloggnitz and three additional intermediate construction accesses in Göstritz, in the Fröschnitzgraben and in Grautschenhof. For reasons of organization, scheduling and topography, the tunnel is divided into three construction lots (Gobiet & Wagner 2013). The eastern contract "SBT1.1 Tunnel Gloggnitz" is under construction since the middle of 2015 (Wagner et al. 2015), the middle contract "SBT2.1 Tunnel Froschnitzgraben" started at the beginning of 2014 (Daller et al. 2013) and the western contract "SBT3.1 Tunnel Grautschenhof" will follow in spring of 2016 (Klais et al. 2015).
Subject of this article is the methodology of the geotechnical design for the entire tunnel system. The geotechnical design work started with the commissioning of the project in early 2005 and was done step-by-step more in detail in every design phase of the project.