SUCCESS STORY AT BOMLAFJORD

This article relates the story of the 7.9km long Bomlafjord Tunnel in Norway, which is Europe's longest under-sea tunnel. It is part of the Triangle Link Project, which will connect three island communities to the mainland. Construction of the north and south ends of the tunnels began in February 1995 and September 1997, respectively, and boring was completed in September 1999. The tunnel and E-37 coast road will open to traffic in December 2000 and the whole project will be completed in April 2001. The tunnel's geology is very varied, and includes gneiss and schists, and a seismic survey detected a major fault. Because 3.4km of the tunnel is under the sea, very extensive site investigations, using about 7.8km of seismic profiles and 1485m of core drilling, had to be conducted. They made a very important contribution to the success of the tunnel's construction. The tunnel was excavated in drill+blast from both ends, using an Atlas Copco 183 tunnel boring machine (TBM) and other equipment. The tunnel cross section is 82m squared. Each round of blasting was followed by a geological examination, and grouting was applied where there was ground water leakage. The major weakness zones were supported by spilling bolts and a new shotcrete method containing alkali-free accelerator.