The world's longest road tunnel.

The 24.5 km Laerdal tunnel in western Norway, whose excavation is almost complete, has made full use of the country's hard-rock tunnelling expertise. The 70-120 MPa hard Precambrian gneisses provided generally good conditions, but the overburden of over 800 m led to high vertical stress and the danger of rock bursts. Excavation has been mainly by drilling and blasting. The use of large-scale mucking plant is one of the project's unusual aspects. A complex fan ventilation system was monitored and controlled by high-technology communication links and a computerised centre set up at the Laerdal portal, while adjustments could also be made by workers at the face. Support was by wet shotcrete with a steel fibre content of 40 kg/m3, enhanced by galvanised steel rock bolts.
The 24.5 km Laerdal tunnel in western Norway, whose excavation is almost complete, has made full use of the country's hard-rock tunnelling expertise. The 70-120 MPa hard Precambrian gneisses provided generally good conditions, but the overburden of over 800 m led to high vertical stress and the danger of rock bursts. Excavation has been mainly by drilling and blasting. The use of large-scale mucking plant is one of the project's unusual aspects. A complex fan ventilation system was monitored and controlled by high-technology communication links and a computerised centre set up at the Laerdal portal, while adjustments could also be made by workers at the face. Support was by wet shotcrete with a steel fibre content of 40 kg/m3, enhanced by galvanised steel rock bolts.