The rail link, to be renamed the Airport Line when it becomes operational, forms part of the METRONET vision to create liveable communities connected by world class public transport. The line will spur off the existing Midland Line near Bayswater Station and run to High Wycombe through twin-bored tunnels.
During construction in 2018 a leak developed during the installation of the first tunnel cross passage, Cross Passage Dundas, into Tunnel One, approximately 200m north of the Forrestfield Station site and the launching point for the Tunnel Boring Machines. As a result, water and silt entered rapidly into the tunnel at up to 60L/sec resulting in loss of ground around the tunnel and subsequently leading to the formation of a sinkhole at the surface alongside and partly beneath Dundas Road. The groundwater pressure, and the associated lack of support to the tunnel lining, caused permanent localised distortion to the tunnel shape and movement of the segments which make up the tunnel lining, ultimately damaging a 26m-long section of Tunnel One (16 rings).
A cast iron steel ring known as the SGI lining was installed to reinforce the damaged area. Given the type of project and level of protection required to this vital asset, it was determined that passive fire protection should be provided to the SGI lining.
