The highly variable nature of deeply weathered Oporto granite posed significant challenges in the driving of the 2.3km long Cline and the 4km long S line of the Oporto Metro project. Two 8.7m diameter Herrenknecht EPB TBMs were used to excavate these tunnels ...

In tunnelling through heterogeneous rock masses, such as the flysch, it is important to attempt to obtain reliable estimates of potential tunnelling problems as early as possible. This enables the tunnel designer to focus on the selection of optimum routes ...