The largest tunnel boring machine in the southern hemisphere is gearing up to break ground in the coming days on the Western Harbour Tunnel project.
Patyegarang, the first of two tunnel boring machines, will soon begin her journey 44.7 metres below Birchgrove Oval, under Sydney’s iconic Harbour towards Waverton, following final testing over the weekend.
The record-breaking machines are the largest to have ever been assembled underground, measuring 15.7 metres in diameter and weighing 4,350 tonnes. As they excavate, the machines will line and support the tunnels using around 13,000 pre-cast concrete segments.
Both tunnel boring machines are being supported by another record-breaking piece of engineering, an underground slurry treatment plant.
The plant can pump up to three million litres of slurry (water and clay) per hour to each boring machine face, which keeps it stable while it excavates under Sydney Harbour’s soft marine sediments.
Slurry treatment plans are usually located on the surface, but the Western Harbour Tunnel plant has been built entirely underground to reduce impact to the local community.
The plant measures more than 100 metres long and up to 15-metres-tall and is the first slurry treatment plant of this size to have been constructed underground in the world.
The slurry treatment filters and reconditions the slurry before sending it back to the tunnel boring machines for reuse, as well as separating out the dry spoil portion which will be trucked out of the tunnel via WestConnex for use on other projects.
Western Harbour Tunnel’s two tunnel boring machines are named after notable Aboriginal women, Patyegarang and Barangaroo.
The assembly of the 2nd machine, Barangaroo, is 94 per cent complete and she is expected to begin tunnelling in around four weeks.
The tunnel boring machines will excavate the final 1.5 kilometre stretch of the twin motorway tunnels under Sydney Harbour, reaching depths of 50 metres below sea level.
They will operate 24/7 and will have 40 people working on them at any one time.
The 6.5-kilometre Western Harbour Tunnel is set to open to traffic in 2028 with overall excavation now at 81.35 per cent complete. It will remain in public hands.
“This is a major milestone for the Western Harbour Tunnel project, marking the beginning of the final stage of excavation under Sydney Harbour,” said NSW Minister for Roads, Jenny Aitchison.
“Assembling these mega machines entirely underground has been incredibly complex work and the team is doing a fantastic job.
“When it’s complete, the Western Harbour Tunnel will provide a seamless connection from the Warringah Freeway and North Sydney to WestConnex at Rozelle Interchange.
“Building and operating the tunnel boring machine’s slurry treatment plant underground is a not only a major win for the local community, but a significant engineering first for Australia and the world.”
.jpg)
