Experience with the TBM drive through clay rocks with low strength in the Boßler Tunnel

The Tunnel Albaufstieg consortium won the contract with an alternative proposal to drive a section about 2.8 km long of the 8.8 km long Boßler Tunnel with a tunnel boring machine (TBM). The next section, where squeezing conditions were forecast, was to be tunnelled by the shotcrete method according to the tender documents. Manifold and extensive additional investigations delivered the basis for the extension of the TBM drive along the entire length of the Boßler Tunnels. The driving of the section through the Aalenian 1 geology was problem free due to the low strengths and good cuttability of the rock mass combined with its impermeability. The next section in the intercalation of claystone and sandstone of the Aalenian 2 was much more differentiated but managable. The breakthrough of the east bore of the Boßler Tunnel confirms to the responsible people for the client and contractor that the decision to follow the aim of consistent mechanised tunnelling had been correct.