Immersed tunnel design in subarctic rivers

The demand for tunnels crossing waterways in urban areas is expanding into colder regions, with immersed tunnels an increasingly competitive alternative for waterway crossings. Recent examples of new immersed tunnels affected by cold weather include the Bjørvika, Söderstrum, and Marieholm tunnels in Norway and Sweden. This article aims to describe the practical and technical issues related to applying the immersed tunnel construction method to colder regions for them to stay competitive.

An initial distinction can be made between tunnels crossing large water bodies and tunnels crossing rivers based on the differences in their ice regimes. For example, one of the main ice related issues for immersed tunnels crossing seas and lakes is ice pile-up, which results in heavy loading of the approaches and mechanical scour of the seabed. This is an issue which is relatively well documented and has been taken into account in projects like the Øresund tunnel. The ice regime of a river is quite different, where issues for immersed tunnels have thus far gone undocumented. Subarctic issues typical in river ice regimes may include ice jams, anchor ice, surges, water level drops, and thermal expansion of ice, as well as unfavorable material behavior.