Cases of instability caused by weakness zones in Norwegian tunnels

• Published in: Bulletin of engineering geology and the environment Vol. 70; no. 1; pp. 7 - 13
• Main Author: Nilsen, Bjørn
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01.02.2011; Springer-Verlag
• Subjects: Cave-in; Earth and Environmental Science; Earth Sciences; Fault; Faults; Foundations; Geoecology/Natural Processes; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Instability; Nature Conservation; Original Paper; Rock; smectite; Smectites; Stability; Swelling; Swelling clay; Tunnelling; Tunnels (transportation); Weakness zone; Cave-in; Swelling clay; Zone de faiblesse; Smectite; Weakness zone; Débourrage; Instability; Instabilité; Fault; Faille; Argile gonflante
• ISSN: 1435-9529; 1435-9537
• DOI: 10.1007/s10064-010-0331-x

Cave-in and rock fall are rare occurrences in Norwegian tunnelling today. Despite all precautions that are taken to prevent such incidents from happening, a few serious cases have occurred during the last few years. In this paper, one recent case of cave-in during tunnelling (the Atlanterhav tunnel) and two cases of rock fall/cave-in after completion of the project (the Oslofjord and Hanekleiv tunnels) are discussed. The main focus is on discussion and comparison of the rock engineering aspects of these incidents, and on the lessons that may be learnt from them. It is concluded that the presence of swelling clay (smectite) has been a main cause of instability, although low internal friction may be a destabilizing factor at least as important as swelling, and that the most difficult situation is a combination of very poor quality material and high water pressure in faults/weakness zones.