Tunnel boring machine – Exit of the citybound tunnel after breakthrough, what happens next?

After tunnelling under Yarraville, the West Gate Tunnel Project’s tunnel boring machines (TBMs) have arrived at their destinations.

Vida arrived at the citybound tunnel entrance site on the West Gate Freeway near Williamstown Road in February 2023. The inbound tunnel is 2.8km long.

Bella, the outbound TBM, tunnelled 4km under Williamstown to reach the tunnel exit just east of  Millers Road on the West Gate Freeway in early May.

Both journeys culminate with a ‘breakthrough’, when the TBM pushes through the concrete or rock wall into a retrieval pit, which marks the end of the tunnel boring works.

Following the breakthrough, the machines are broken down in to pieces, and mostly moved offsite via trucks.

Major works then continue within the tunnel to install services, lighting and the new road and motorway management systems.

Tunnel boring machine, Vida

With careful planning and monitoring in place, the TBM breaks through the natural rock wall into what is known as the “retrieval pit” where it stops. From here, the machine is broken down into smaller sections ready for transport. It is then carefully lifted onto trucks to be taken back to the West Gate Tunnel Project tunnelling hub on Whitehall Street, to the former flower market in Footscray, or for storage before parts are either recycled or sent back to the manufacturer for reuse.

Dismantling and removing the full TBM takes several months with works and transport happening both day and night.

Tunnel boring machine, Bella

As there is more space available at the outbound tunnel exit where Bella’s journey ends, the second TBM removal follows a difference process. While many components are still removed, the extra space here allows the largest parts of the machine to remain right next to where it stops. This option also reduces time, noise and traffic  disruptions by sliding parts of the TBM to a space within the breakthrough area where it can be buried. The TBM is then filled with, and enclosed in, concrete before being covered by soil.

Using concrete to stabilise and bury materials is a common construction technique and endorsement by relevant authorities has been obtained.

How we will keep you updated

• >Works notifications distributed to the local community
• Updates on the West Gate Tunnel Project website and social media accounts
• SMS alerts for people who wish to subscribe
• Monthly drop in sessions in our information centre on Somerville Road
• Pop ups near the portal.

Contact us

Our dedicated Community Relations team is available 24 hours a day, seven days a week to speak with anyone who has any concerns about construction impacts.
We appreciate your patience and understanding as we finish this important milestone for the West Gate Tunnel Project.