The two TBMs both weigh in excess of 4,000tonnes, are 90m long and are boring diameters of 15.6m. Gillian and Zelda completed their first drives in March 2025, having started in September 2024 and August 2024 respectively. Both TBMs bored over 1.9km for their initial drives (around 36% of the total distance they have to complete), with around 7,700 tunnel segments having been installed in each bore.
When complete, each of the twin tube tunnels will carry three lanes of traffic, measure 6.5km in length and will be at a depth of 45m. The new tunnels will reduce congestion on the existing road network and cut journey times for drivers in and around Melbourne.
Other work forming part of the project includes changing the alignment of Bullen Road, upgrades to the M80 Ring Road and Eastern Freeway and building foundations for the new link roads to the tunnels.
The project is being funded jointly by the Australian Government and Victorian Government, with completion expected in 2028. The project was originally expected to come with a pricetag of US$6.25 billion (A$10 billion) but now looks as if could cost as much as $16.24 billion (A$26 billion). The project is being carried out by the SPARK joint venture, which includes the Italian contractor Webuild.
