The successful implementation of a major infrastructure project demands not only the processing of technical questions but also the solution of numerous legal problems and the organisation of an intensive communication process. The article offers an overview of the work of the project team at the ÖBB‐Infrastruktur AG, which has been working intensively on the implementation of the New Semmering Base Tunnel project for eight years. The project has the most stringent requirements due to its project history and complexity and poses great challenges for all those involved. Für die erfolgreiche Umsetzung eines großen Infrastrukturprojekts sind neben der Abarbeitung technischer Fragestellungen auch unzählige rechtliche Probleme zu lösen und ein intensiver Kommunikationsprozess zu betreiben. Der Beitrag gibt einen Einblick in die Arbeit des Projektteams der ÖBB‐Infrastruktur AG, das seit acht Jahren intensiv an der Umsetzung des Projekts Semmering‐Basistunnel neu arbeitet. Das Projekt weist aufgrund seiner Projekthistorie und Komplexität höchste Anforderungen auf und stellt alle Beteiligten vor immer neue Herausforderungen.

The Semmering Base Tunnel (SBT) is about 27.3 km long and is being driven from the portal at Gloggnitz and from three intermediate construction accesses in Göstritz, Fröschnitzgraben and Grautschenhof. The main components of the tunnel system are the two single‐track running tunnels, cross passages at a maximum spacing of 500 m and an emergency station in the middle tunnel section, with two shafts about 400 m deep for ventilation and extraction in case of an incident. For organisational, scheduling and topographical reasons, the tunnel is divided into three construction contracts. The eastern contract section SBT1.1 ”Tunnel Gloggnitz“ has been under construction since mid 2015. Construction started on contract section SBT2.1 ”Tunnel Fröschnitzgraben“ at the start of 2014. The western contract section SBT3.1 ”Tunnel Grautschenhof“ has been under construction since May 2016.

During the construction of the Semmering Base Tunnel, Lot SBT1.1, the drives have already encountered several fault zones in the Greywacke Zone. Because of the high overburden, the exact position of these fault zones is unknown at tunnel level; a common problem for all tunnelling projects in mountainous regions. Simple exploration drilling techniques such as percussion drillings, where only cuttings and not cores are won, do not always provide enough information to precisely specify the position of the fault zones or their nature ahead of the face. This is reason enough to examine other possibilities for the short‐term prediction of fault zones with differing characteristics ahead of the face. Usually displacement data evaluation provides the basis for a short‐term prediction of the system behaviour. However, experiences from Lot SBT1.1 show that applying this approach solely does not always yield satisfying results. A further systematic analysis of selected geological data can improve the short‐term prediction. In particular, changes of discontinuity and rock mass characteristics mapped at the tunnel face are analysed to spot significant trends indicating fault zones ahead of the face. These trends are then related to and verified by the results of displacement data evaluation. This combination of rock mass characteristics mapped at the face and state‐of‐the‐art evaluation of displacement data has helped to improve the reliability of short‐term predictions during the tunnel excavation.

The New Semmering Base Tunnel (SBTn) has been designed with a flat gradient to meet the requirement for uniform high‐speed rail infrastructure for the new Südbahn line, which is considered an internationally significant transport corridor for Austria as an industrial location. The 27.3 km tunnel is divided into a number of construction sections with separate contracts due to the geological and hydrogeological conditions. In addition to the tunnel drives from the Gloggnitz portal, the tunnel will also be driven from three intermediate starting points. The individual tunnelling contracts will be started at intervals of about one year. The first tunnelling contract starts in 2014 in the Fröschnitzgraben, the drives in Gloggnitz and the intermediate starting point at Göstritz in 2015 and the tunnel drive in Grautschenhof from 2016. From 2021, when all tunnelling works have been completed and the structure of the two running tunnels has been completed, the installation of the tunnel equipment will start. Opening for service is intended for the end of 2014. Der Semmering‐Basistunnel neu (SBTn) wurde gemäß den Vorgaben zur Bereitstellung einer einheitlich leistungsfähigen Eisenbahninfrastruktur für die neue Südbahn, die als international bedeutende Verkehrsachse für den Wirtschaftsstandort Österreich gilt, mit einer flachen Neigung konzipiert. Der 27,3 km lange Tunnel wird aufgrund der geologischen und hydrogeologischen Verhältnisse sowie der baulogistischen und tunnelbautechnischen Anforderungen in mehreren Bauabschnitten mit unterschiedlichen Baulosen errichtet. Neben den Vortrieben vom Portal Gloggnitz wird der Tunnel über drei Zwischenangriffe aufgefahren. Die einzelnen Tunnelbaulose werden gestaffelt in Abständen von etwa einem Jahr begonnen. Das erste Tunnelbaulos startet 2014 im Fröschnitzgraben, 2015 beginnen die Vortriebe in Gloggnitz und beim Zwischenangriff Göstritz, ab 2016 erfolgt der Tunnelvortrieb in Grautschenhof. Ab 2021, wenn alle Vortriebsarbeiten abgeschlossen und die beiden Tunnelröhren im Rohbau durchgängig fertiggestellt sind, beginnt der Einbau der Tunnelausrüstung. Die Inbetriebnahme ist Ende 2024 vorgesehen.

One of the major fault zones in the Semmering area runs along the Auebach Valley. In this fault zone a combination of soft fault rocks and water bearing hard rocks led to extremely challenging conditions in the design and execution of the tunnel. In difficult conditions, overlapping exploratory drillings in front of tunnel drive are essential to improve the geological‐hydrogeological model and to assess geotechnical risks. However, in the encountered geological‐hydrogeological conditions, the well‐established exploratory drilling methods reached their limits. Despite the ongoing risk analysis, a very large‐scale water and ground inflow with subsequent tunnel face collapse and development of a sinkhole on the surface occurred during the tunnelling. This paper describes the causes of the incident and the development of procedures to cope with the problem. In addition to the geological‐geotechnical analyses, the article also discusses the limitations of geotechnical surveillance in complex heterogeneous rock masses.