A major milestone has been reached in the delivery of Sydney’s first new road harbour crossing in almost 30 years, with tunnelling completed on twin underground caverns at Birchgrove.
Western Harbour Tunnel crews have completed construction of massive twin caverns that will serve as the launch chambers for the largest twin tunnel boring machines (TBMs) in the southern hemisphere, Barangaroo and Patyegarang.
Together these technological behemoths will dig the 1.5 kilometre underwater section of the Tunnel up to 50 metres below sea level to Waverton.
The tunnel is expected to deliver travel time savings to motorists and reduce traffic on the Western Distributor by 35 per cent, in the Harbour Tunnel by 20 per cent and on the Sydney Harbour Bridge by 17 per cent.
The two 28-metre high caverns are among the largest ever excavated in Australia, each big enough to fit 22 Olympic swimming pools or six Emerald-class Sydney Ferries. They are located just 230 metres from the edge of Sydney Harbour ready for the TBMs’ epic dive.
The milestone comes as the second TBM arrived in Sydney on 21 October, joining its twin, which landed in August.
Each machine is an engineering marvel; 137 metres long and weighing more than 4,300 tonnes which is the equivalent of 88 double decker buses. The pair will carve a 1.5-kilometre route under Sydney Harbour to the Warringah Freeway at North Sydney.
Over the coming months, workers will assemble the TBMs piece by piece inside the Birchgrove caverns using a 500-tonne gantry crane. Once launched, they’ll tunnel around the clock, supported by 40 skilled workers per shift, as they begin their journey beneath the harbour.
The TBMs will begin excavating under the harbour in the first half of 2026 once the TBMs, comprising 263 major parts each, have been assembled in painstaking correct order. TBM assembly will take several months. They are expected to take around a year to complete their work.
When complete, the Western Harbour Tunnel will provide a seamless 6.5 km connection between the Warringah Freeway and the Rozelle Interchange, reducing congestion, improving travel times, and strengthening connections across the city’s north, west and south.
The Western Harbour Tunnel is on track to open to traffic in 2028 and will remain in public ownership, ensuring the long-term benefits of this investment stay with the people of NSW. The project is supporting 7,000 jobs over the course of construction.
NSW Minister for Roads, Jenny Aitchison, said that the Western Harbour Tunnel is one step closer to delivery.
“This is a once-in-a-generation project, with the State Government on track to deliver Sydney’s third road harbour crossing,” Aitchison said.
“These giant caverns are vast enough to fit six Emerald class Sydney ferries each, but once the TBMs are assembled inside them, there will only be around 1-2 metres between each TBM and the launch chamber walls.
“The scale of this project is absolutely breathtaking. More than 4,800,000 tonnes of material already have been excavated across the Western Harbour Tunnel project to date.
“The Western Harbour Tunnel TBMs are the largest in the Southern Hemisphere and the largest in the world to be assembled underground.
“In a few days, the TBM parts will be loaded onto specialised heavy vehicles and transported into the launch chambers via the City West Link portal.”
