ABSTRACT
Tunnel face seismic tomography using a pair of boreholes that was performed by NGI at the Oslo Fjellinjen Tunnel, in the late 1980’s, was used to help the contractor plan for ground freezing in one tube, while careful multiple drift excavation was performed in the other tube. The 2 13 m span motorway tunnel beneath the Oslo downtown harbour district, passed through a wide regional fault zone with 2 to 4 m of crushed alum shale over the arch, underlying 20-30 m of soft, sensitive marine clays. The advantages of the ahead-of-the-event data far outweighed the relatively short stoppages and modest cost involved.
