The site facility area Fröschnitzgraben of the SBT2.1 section of the Semmering Base Tunnel (SBT) is located in the floor of the Fröschnitzgraben valley and is surrounded by valley slopes in the east and the west. Therefore, cuts and embankments are required for the construction of the site facility area. Based on investigation results it was assumed that the slope is in a limit equilibrium, which required massive support measures to ensure a sufficient level of safety especially considering earthquake effects. A failure of the slope would endanger the site facility area and a public road. To monitor the slope displacements during construction of the site facility area a comprehensive monitoring program including various monitoring methods was implemented. According to the results of the numerical calculations, the expected target behavior and warning levels were defined in the geotechnical safety management plan, including various countermeasures.
The Semmering Base Tunnel (SBT) is about 27.3 km long with two portals in Gloggnitz and Mürzzuschlag. The tunnel will be excavated from the portal in Gloggnitz and the three intermediate construction accesses in Göstritz, Fröschnitzgraben and Grautschenhof. Subject of this article is the contract section SBT2.1 „Tunnel Fröschnitzgraben". Further information on the SBT and SBT2.1 has already been published (Daller et al. 2013).
The site facility area is located in the floor of the Fröschnitzgraben valley and is surrounded by valley slopes in the east and the west. To build a site facility area of sufficient size extensive support measures are required. In order to ensure a safe and economic approach, a geotechnical safety management was implemented comparable to that in conventional tunneling (Moritz et al. 2011 and Austrian Society for Geomechanics 2014).
The aim of this paper is to describe the monitoring measures and the methods within the geotechnical safety management.