ABSTRACT
The many undersea tunnels along the coast of Norway offer excellent opportunities to study the key factors determining stability and water leakage in hard rock subsea tunnels. About 30 such tunnels have been constructed in Norway the last 20 years, all of them excavated by drill and blast. The longest tunnel is 7.9 km with its deepest point 260 metres below sea level. Although all tunnels are located in Precambrian or Palaeozoic rocks, some of them have encountered complex faulting or less competent rocks like shale and schist. The severe tunnelling problems met in these tunnels emphasise the need of a better understanding of the key factors determining stability and water leakage of such projects. This has been discussed based on the experience from several completed projects.
