PREVENTION IS BETTER THAN CURE

Conditions for the 3.5 km long Aalesund-Ellingsoey and 4.2 km long Ellingsoey-Valderoey subsea road tunnels on the West coast of Norway have mainly been as expected from the pre-investigations. Refraction seismic profiles indicated the location of the major weakness zones and faults; systematic probe drilling during construction on the subsea sections, and partly under land, has given warning of water leakages into the tunnel and stability problems. This has allowed efficient pregrouting to reduce water leakage and necessary rock reinforcement and support to take place in a flexible routine. (Author/TRRL)