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.

The first call for tenders for the three tunnelling contracts of the New Semmering Base Tunnel is one of the highest value tendering processes in the Second Austrian Republic. The enormous magnitude of the construction works and access and development of the site for the tunnelling works represent a great logistical challenge. This situation also had to be considered in the form of contract. Die erste Ausschreibung für die drei Tunnelbaulose des Semmering‐Basistunnels neu ist eines der höchsten Vergabeverfahren der Zweiten Republik. Der enorme Bauumfang sowie die Erschließung der Baustelle und der Vortriebe stellen eine große logistische Herausforderung dar. Diesem Umstand musste auch in der Vertragsgestaltung Rechnung getragen werden.

With the ruling of the Austrian federal administrative court in May 2015, all necessary permits have now been issued for the construction of the Semmering Base Tunnel. The project is one of the most reviewed projects in Austria, and as the other authorities had done previously, the federal administrative court once again confirmed the environmental acceptability of the project. Until the judgement of the constitutional high court with the revocation of the construction permit (served on 10 February 2014), all necessary preliminary works had been carried out on schedule and within budget since 2012. The preliminary works started in the Fröschnitzgraben in January 2014 could however only be continued with limitations on the basis of official notifications issued without preliminary investigation. No construction could take place at the landfill site due to the lack of a decision under the waste management law. Only after the ruling by the federal administrative court could the construction works be resumed at full pace. Works started soon after in the Gloggnitz tunnel section in Lower Austria on 1 July 2015. Construction works for the third and final tunnel section, Grautschenhof , were officially tendered on 2 September 2015. By 2016, all tunnel construction contracts should be continuously under construction.Für den Bau des Semmering‐Basistunnels liegen nach der erfolgten Entscheidung des Bundesverwaltungsgerichts im Mai 2015 nun alle erforderlichen Genehmigungen vor. Das Projekt ist eines der meistgeprüften Projekte Österreichs, und wie schon die anderen Behörden zuvor, hat auch das Bundesverwaltungsgericht erneut die Umweltverträglichkeit des Projekts bestätigt. Bis zum Urteil des Verwaltungsgerichthofs mit der Aufhebung des Baubescheids (Zustellung 10. Februar 2014) konnten alle erforderlichen Vorarbeiten seit 2012 im Zeit‐ und Kostenrahmen umgesetzt werden. Die im Fröschnitzgraben im Januar 2014 begonnen Vorarbeiten konnten jedoch nur eingeschränkt auf Basis von Mandatsbescheiden fortgeführt werden. In der Deponie konnte wegen des Fehlens des AWG‐Bescheids gar nicht gebaut werden. Erst mit Vorliegen der Entscheidung durch das Bundesverwaltungsgericht konnten die Bauarbeiten wieder volle Fahrt aufnehmen. Der Baubeginn des niederösterreichischen Tunnelabschnitts Gloggnitz erfolgte bereits am 1. Juli 2015. Die Bauarbeiten des dritten und letzten Tunnelabschnitts Grautschenhof wurden am 2. September 2015 öffentlich ausgeschrieben. Ab Frühjahr 2016 sind voraussichtlich alle Tunnelbaulose durchgängig in Bau.

At the construction lot SBT 2.1 ”Tunnel Fröschnitzgraben“ of the Semmering Base Tunnel (SBT) in Austria caverns with a cross section up to 300 m2 are excavated in a depth of approximately 400 m, which are the central part of the emergency station. The site arrangement results in a complex situation of large cross sections within a small area. Additionally, complex ground conditions exist, because the degree of fracturing of the rock mass differs frequently and the rock mass strength is occasionally very low. Especially at the intersection of the caverns displacements increase over a long period of time. The observed system behavior is described and analyzed based on the geotechnical design taking the encountered ground conditions into account. Sequences of rock mass sections with different stiffness and strength are of high geomechanical significance due to stress concentrations in the competent areas. This had particular impact on the observed system behavior. With regard to the stability of the overall system influences of various drives and the excavation of large cross sections in several steps must be considered. Moreover, an influence of the excavation size on the extension of the area with displacement increases or stress redistributions must be taken into account.

Contract SBT2.1 Tunnel Fröschnitzgraben is the central and longest construction section of the Semmering Base Tunnel, including 13 km of tunnelling from the intermediate access in Fröschnitzgraben towards Gloggnitz and Mürzzuschlag. The approx. 4 km long section towards Mürzzuschlag is being excavated by drill and blast, and the 9 km section towards Gloggnitz is being driven by two tunnel boring machines. Before the start of the actual construction of the running tunnels, the two shafts about 400 m deep had to be sunk using an innovative concept. Considerable changes are also noticeable above ground: the filling level of the landfill site in Longsgraben is rising constantly.