Observational method as risk management tool: the Hvalfjorour tunnel project, Iceland

Rock tunnel construction is associated with considerable geotechnical uncertainty, often due to limited knowledge about the ground conditions. This warrants the use of stringent risk management procedures to reduce the likelihood of cost increases, delays, and structural failure events. The observational method is often promoted as a tool to achieve cost-effective designs in cases of large geotechnical uncertainty, but its practical use is still limited. One reason may be the lack of guidelines and experiences from previous projects where the observational method has been used. In this paper, we therefore present a case study of the design and construction of the tunnel under the Hvalfjorour fjord in Iceland, where the observational method played a key role in the risk management that was performed to deal with the challenging geological conditions at the site. The project was a success and completed four months earlier than originally planned. In light of the case study, we discuss the definition of the observational method in Eurocode 7 and the related contractual aspects to consider in such projects.

Automated summary

Rock tunnel construction involves significant geotechnical uncertainty and requires stringent risk management procedures. The observational method is promoted as an effective tool, but its practical application is limited. This paper presents a case study of a tunnel construction project in Iceland where the observational method played a key role in managing the challenging geological conditions. The study discusses the definition of the observational method in Eurocode 7 and related contractual aspects.