Ramboll has comprehensive and long-term experience of tunnelling in Scandinavia, where the geology is characterised by hard rocks such as gneiss, greenstone and granite. Our expertise covers all types of hard rock tunnelling methods including continuous pre-grouting to exclude water inflow, blasting, boring, post-grouting and using the Q-system.
Drill and blast
Most of the tunnels we work on in Scandinavian hard rock conditions are excavated using drill and blast techniques. Examples of our drill and blast projects are Triangeln Station in Sweden — part of the Malmö rail tunnel project — and the refurbishment of Päijänne Water Tunnel in Finland.
Where the rock is soft enough not to require blasting, Ramboll’s tunnel designs use alternative excavation methods such as road headers and tunnel boring machines (TBMs). Modern TBMs are ideal for long continuous tunnels that contain a variety of rock conditions.
The Hallandsås tunnel project in western Sweden has shown how TBMs can overcome even the most challenging water-bearing mixed ground conditions. In places, the saturated rock had to be frozen before a TBM could be deployed. We provided digital modelling, non-destructive testing and audit advice for the 8.7km railway tunnel.
Ramboll’s designs for tunnelling through rock take account of the Q-system, which describes the quality and stability of the rock mass and evaluates the tunnel supports required.
The Q-system was developed at the Norwegian Geotechnical Institute, and has been updated periodically to relate to current practice.