Excavating through hard rock formations with TBM: Technical challenges of the Follo Line Project

The Follo Line Project is Norway’s largest infrastructure project and Scandinavia’s longest railway tunnel. Excavation is done by four Double Shield Tunnel Boring Machines (DS TBMs) all with a diameter of 9.96 m. It is the first tunnel in Norway built with a precast segment lining. Excavation in the Norwegian extreme hard rock conditions with ground water has defined the main challenges of the Project. The experience gained so far, at a progress of 83% on the TBM drives, has been extremely positive. TBM penetration, cutter wear and TBM advance rates are well within the expectations. The management of ground water has been more of a challenge than expected. To control water inflow, pre-excavation grouting has been successfully performed although compromising the TBM advance rate but with satisfying results.