Semmering Base Tunnel – Large Caverns in Challenging Conditions
Semmering Base Tunnel, one of the major infrastructure projects in Europe, consists of two 27.3 km long single-track tunnels, numerous cross passages and a complex underground emergency station with two, more than 420 m deep, shafts. Temporary access is provided by a 1.2 km long access tunnel, with two 120 m subsurface shafts, and two 100 m shafts from the surface. Various types of large caverns are planned, which are either foreseen temporarily for construction purposes such as intermediate access and space for site installations, or permanently for the underground emergency station. The dimensions of the larger caverns are in the range of 25 m by 16 m. The maximum overburden above the caverns is app. 500 m in difficult geological conditions with large fault zones and extensive water inflow, which require complex heading concepts, extensive support measures and partially special ground improvement works such as grouting. The applied construction method for the caverns and the main part of the single track tubes is SEM/NATM whereas the remaining sections are excavated by means of TBM. Works are ongoing from 2014 until 2026.