Performance of different diameter Double Shield TBMs: experiences from the excavation of exploratory tunnel and main tubes of the Italian lot Mules 2-3 – Brenner Base Tunnel

The Brenner Base Tunnel is a 64 km long underground railway connection under construction between Italy and Austria. The project mainly consists of two main one-track tunnels and a central exploratory tunnel 12 m below them. Considering that the three tunnels intersected the same rock masses and fault zones, the paper analyses the scale factor displayed by selected machine parameters in relation to the tunnel diameter, TBM characteristics and rock mass conditions. Final considerations about the performance of the three TBMs, also in the context of comparable case-histories, are addressed.