Experience from TBM excavation obtained in the Follo Line Project

In some projects the selection of TBM is straight forward, but in others all boundary conditions have to be carefully evaluated in order to make the most suitable choice. For underground projects the actual ground conditions remain to certain degree always unknown, regardless of the performed ground investigations. This means specific parameters, which may have significant impact on the project success, might be over- or underestimated. Such parameters could be different rock mass properties as well as water ingress. This paper discusses some relevant parameters for TBM selection in hard rock environment, mainly based on the experience gained in the Follo Line Project in Norway. Four double shield TBMs with excavation diameter of 9.96 m are drilling through various kinds of gneisses with banding and lenses of amphibolite and pegmatite. More than 75 % of a total of 36 km have already been excavated with several kilometres of pre-excavation grouting for reduction of water ingress. Furthermore, potential improvements for TBMs will be proposed in order to make TBMs even more successful.