At the construction Lot SBT 3.1 of the Semmering Base Tunnel long-term displacement increases caused an overutilization of the support measures over a length of approximately 100m behind the excavation face. It was concluded that these increases were caused by a strain softening of the rock mass. In numerical calculations visco-elastic and visco-plastic material models are used very often to model long-term rock mass behavior. In the present case a linear elastic – ideal plastic material model with a Mohr-Coulomb failure criterion in combination with a creep function was used to model long-term behavior. The strength and stiffness values as well as the creep values of the rock mass were identified based on a curve-fitting of monitored displacements to limit excavation interruptions due to testing of the rock mass and parameter identification for numerical modelling. Support measures and construction sequences for further excavation were designed based on the calculation results.
The Semmering Base Tunnel (SBT) is situated in Austria / Europe and is part of the Baltic-Adriatic Corridor, which is one of the most important cross-Alpine lines in Europe. The tunnel is constructed as a two-tube railroad tunnel with a length of about 27.3km and is excavated from the portal at Gloggnitz and three intermediate construction accesses. For a detailed description of the project refer to Gobiet et al. (2017).
The geological conditions in the project area are characterized by a tectonically extremely complex rock mass structure. The tunnel alignment passes through several tectonic nappe units, meets various crystalline rock complexes and Permo-Mesozoic cap rocks and is intersected by numerous tectonic fault zones.
The project area of the Semmering Base Tunnel is characterized by very complex rock mass conditions consisting of an intensive fold, nappe and scale structure. The tunnel lies within an inverse rock sequence and contains karstified carbonate rocks and Semmering quartzite of the Permo-Mesozoic as well as overlying mica shists to quartz phyllites. The Tunnel section issued in this article is in the West part of the tunnel towards the portal at Mürzzuschlag and lies in the tectonically heavily disturbed transition area from carbonate breccias and quartzite to quartz phyllites with an overburden of around 225m. The rock mass conditions are characterized by small-scale changes of the degree of fragmentation and strength properties and therefore were very heterogenous. Additionally, cataclastic fault zones of different thickness (range from decimeter to meter) intersect the rock mass. Pronounced asymmetries in the elevation of the temporary top heading carriageway as well as distinct failure mechanisms were documented in the excavation face of the bench / invert (Figure 1).
