At the construction lot SBT2.1 of the Semmering Base Tunnel (SBT) in Austria two shafts with a depth of about 400 m were excavated following the principals of the new Austrian tunneling method (NATM). In the design phase several numerical calculations were carried out to dimension the necessary support measures based on different geological and geotechnical circumstances. During construction it was the aim to compare the actual system behavior with the one of the design. Therefore, a comprehensive monitoring program including 3D-displacement monitoring, extensometer measurements and strain gauges was performed. The monitoring results have to be interpreted based on a mechanically correct model representing geological and geotechnical conditions in reality. Therefore, it was necessary to take a transversely isotropic material behavior into account. Depending on the horizontal in-situ stresses a good match of the calculated and the observed displacement pattern was found.
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 (http://www.baltic-adriatic.eu/en/baltic-adriatic-axis/corridor-1).
The tunnel is about 27.3 km long and is excavated from the portal at Gloggnitz and three intermediate construction accesses in Göstritz, in the Fröschnitzgraben and in Grautschenhof. The main elements of the tunnel system are the two single-track running tunnels between Gloggnitz and Mürzzuschlag, cross-passages with a maximum spacing of 500 m and an emergency station near the center of the tunnel with two permanent ventilation shafts. For reasons of organization, scheduling and topography, the tunnel is divided into three construction lots (Gobiet & Wagner 2013). Further information on the SBT and SBT2.1 has already been published (e.g. Daller et al. 2013).
Subject of this article are the two shafts "Fröschnitz 1" and "Froschnitz 2" of the construction lot SBT2.1 "Tunnel Froschnitzgraben" which has been under construction since 2014.
The shafts enable the supply to and disposal of materials from the tunneling works of the two single-track running tunnels and the emergency station. In the final state they will serve as air supply and extraction shafts in case of an incident.
