THE OSLO TUNNEL

This article describes the use of sophisticated blasting techniques to drive a major road tunnel under the centre of Oslo. The Oslo tunnel scheme was chosen as the best of 14 options, after a competition in 1983 to find the best way of removing the traffic bottleneck between the centre and waterfront of Oslo. The tunnel will comprise 2.62 km of underground route, of which 1.52 km will be drilled and blasted through bedrock. The construction scheme for the tunnel and its associated roadworks has four stages: the first, including the hardrock tunnel, is to be completed in 1990, and the fourth stage will be finished around 1994. The total cost of about US $250 million will be met by tolls to be collected from tunnel users. An average traffic flow of 55000 vehicles/day is anticipated when the tunnel opens in 1990, and it should increase to 85000 by the year 2000; theoretical saturation capacity is 110000 vehicles/day, corresponding to a maximum uni-directional flow of 4500 vehicles/hour. The latter part of the paper gives details of the ground conditions, the techniques for excavating the rock tunnel, charging and blasting, grouting and support, the techniques for the cut and cover tunnels, and the project implementation.