ACCIONA has commenced the final tunnelling phase of the New South Wales (NSW) government’s Western Harbour Tunnel, with the tunnel boring machine (TBM) Patyegarang starting excavation beneath Sydney Harbour on 12 June.
The operation began 44.7m beneath Birchgrove Oval, as Patyegarang advances towards Waverton, marking the last stage of underground excavation for the project.
NSW Minister for Roads Jenny Aitchison said: “This is a major milestone for the Western Harbour Tunnel project, marking the beginning of the final stage of excavation under Sydney Harbour.
“Assembling these mega machines entirely underground has been incredibly complex work, and the team is doing a fantastic job.
“Building and operating the tunnel boring machine’s slurry treatment plant underground is not only a major win for the local community, but a significant engineering first for Australia and the world.”
Patyegarang and its sister tunnel boring machine, Barangaroo, are each 15.7m in diameter and weigh approximately 4,350 tonnes (t), making them the largest TBMs in the southern hemisphere ever assembled underground.
Both machines have been engineered to contend with the complex geological conditions found beneath the harbour. The second TBM, Barangaroo, is currently 94% assembled, with tunnelling scheduled to begin in about four weeks.
As excavation progresses, the machines install around 13,000 precast concrete segments to line the tunnels as they are bored.
Supporting the tunnelling effort is a slurry treatment plant, which has been built entirely underground to limit local disruption. This plant is more than 100m long and up to 15m tall, making it one of the largest underground plants of its type to be assembled and operated.
The slurry treatment plant is engineered to pump up to three million litres of slurry per hour to each TBM to maintain tunnel stability. The plant then separates rock material from the slurry, which is recycled for other projects, and returns the processed slurry mixture to the TBMs.
The TBMs, named in honour of notable Aboriginal women, will work around the clock, with approximately 40 people on each machine per shift. Together, they will excavate the final 1.5km of twin tunnels beneath the harbour, reaching depths of up to 50m below sea level.
When completed, the 6.5km Western Harbour Tunnel will link the Warringah Freeway near North Sydney to the WestConnex M4 and M8 at the Rozelle Interchange, allowing vehicles to bypass the central business district. This route is intended to relieve pressure on existing cross-harbour transport links, including the Sydney Harbour Bridge, Sydney Harbour Tunnel, Anzac Bridge, and Western Distributor corridors.
The new motorway marks Sydney’s first road crossing of the harbour in over 30 years and is scheduled to open to traffic in 2028.
The project is divided into two stages. Stage 1, carried out by the John Holland CPB Contractors joint venture (JHCPB), involved the excavation of more than 1.7km of traffic tunnels from Emily Street in Rozelle to Cove Street in Birchgrove, completed between June 2022 and February 2025.
Stage 2, for which ACCIONA was awarded the contract in December 2022, includes the excavation of 4.8km of tunnels from Birchgrove to Cammeray. This stage also includes connections from Stage 1 at Cove Street, Birchgrove, to the Warringah Freeway near North Sydney, tunnelling under Sydney Harbour and the complete tunnel fit-out.
In June 2026, the Department of Planning, Housing and Infrastructure approved the Western Harbour Tunnel Place, Design and Landscape Plan (PDLP) – Part 2, Berrys Bay. This plan sets out the final parkland design for the area.
It incorporates community and stakeholder feedback received in mid-2025 and was developed in collaboration with North Sydney Council, particularly to realise the vision for the Woodley’s Shed community pavilion.
The PDLP also specifies measures for play spaces, native landscape design, and the way heritage and cultural aspects will be integrated into the parkland.
