ABSTRACT
Norway has a long tradition of rock tunneling, however the design of the Drammen Soil Tunnel had to overcome a combination of unique challenges unprecedented in the country. This is a large cross section (156 m2) high-speed railway tunnel excavated in saturated glaciofluvial sediments with little to no cohesion. Dewatering to lower the groundwater table was not permitted, moreover, the tunnel runs beneath Drammen’s streets and buildings with an overburden as low as 8 m, for this reason there were very strict requirements in terms of allowed ground movements. The design solution consists essentially of a 2 to 2.5 m thick jet grout ring around the tunnel excavation profile built from the surface, for this purpose, a total of 2100 jet grout columns, up to 2.5 m in diameter, were installed. The result was a safe tunnel excavation in very stable and dry ground, with minimal deformations and notably low ground movements.
