ABSTRACT
Skanska Norge, in partnership with Arup, is designing and constructing the E5 Råvannstunnel on behalf of Vann og Avløpsetaten. Located west of Oslo, Norway, the new 19.8km long raw water tunnel connects an inlet facility at Holsfjorden to the new water treatment plant in Huse-by. The tunnel lining is formed by conventionally reinforced precast concrete segments with a finished internal diameter of 4.34m and excavated using a double shield gripper type tunnel boring machine. The tunnel lining approach is a departure from the traditional cast-in-place concrete tunnels adopted in the region. This paper discusses the challenges with designing and constructing the precast segmental lining for a complex geological setting at depth varying up to 370m and 15bar of external water pressure. The paper will present the different types of segments designed to meet the challenging loading conditions due to the extreme water pressure and the crossing of severely deteriorated rock formations. Project innovation was required to support the placement of bedding material in these conditions, leading to a specially designed ring with a Bull-Flex insert (similar to the system adopted on Hallandsås tunnel in Sweden) to provide groundwater sealing at the extrados of the segmental lining in longitudinal direction. The state-of-the-art numerical models employed for the radial and circumferential joint design developed for the extremely large hoop forces and TBM thrust forces are also presented.
