The opening of the Forrestfield-Airport Link project will be delayed from 2020 to 2021 following damage to a 26m section of one tunnel.
While the project budget remains unchanged, the timeline has been revised and the first trains are now expected to run on the line in the second half of 2021.
On 22 September 2018, a leak developed in the tunnel-to-tunnel cross passage 200m of the Forrestfield Station site. This led to movement in 16 concrete rings and damage to a 26m section of one tunnel, and a sinkhole alongside Dundas Road.
Investigations have indicated a number of potential causes, including construction defects in the grout block or failure of the join between the tunnel lining and grout. Tunnelling through the grout block and/or vibration from excavation of the cross passage may also have contributed.
New measures will be put in place for the construction of future cross passages to reduce the risk of a similar event occurring. The construction of the next cross passage is due to start in January 2019.
The 26m damaged section of Tunnel 1 has been stabilised and made safe with solid temporary supports. Cement grouting has sealed the leaks and the voids created by ring movement.
WA Minister for Transport, Rita Saffioti, said, “The two tunnel boring machines are now halfway through their journey, and only recently finished digging under the runways at Perth Airport. This is a massive milestone, considering tunnelling under an operating airport has only ever been done a few times across the world.
“Our primary focus is on safety and quality, and that is why today we have set a revised timeframe for the project. It is also to make sure we inform the public of the proposed timeframe as soon as practicable.
“While the delay is unfortunate, this project is being built to last 120 years. I believe the time added to the construction schedule is a small price to pay to ensure we safely deliver this asset which will serve the people of WA for generations.”
Options for a permanent repair include fixing the damage from inside the tunnel or rebuilding the impacted section of tunnel by removing the old rings and casting the new tunnel lining in-situ – either from the surface down, or from within the tunnel. Either solution will be required to achieve the tunnel life of 120 years.
Stabilisation of the ground around Dundas Road is also ongoing, with two traffic lanes to be opened later this month while compaction works continue.
The State Government has repeatedly stressed the importance of safety on the worksite. Safety measures that have been introduced over the last four months include increasing the number of safety compliance officers from two to five, while the contractor has appointed a superintendent of tunnel operations to provide greater oversight and focus on safety.
The Public Transport Authority has conducted 658 safety walks, 430 safety compliance inspections and 72 targeted process inspections during 2018.
A rolling roster of safety staff also monitor site safety for both day and night shifts. Meanwhile, WorkSafe has inspected the site 35 times, and unions close to 300 times.