Watertight segmental lining at drained cross passages under high water gradients

The Follo Line tunnels consist of a watertight single shell segmental lining with gaskets. The cross passages are drained, but watertightness is required between the two structures, which is a challenging boundary condition for design and construction. This paper focuses on the structural design of the intersection between the tunnels and the cross passages, which is performed with considerable effort. Special attention is brought to the water pressures acting in this area. Some of the challenges during project execution are discussed as well.