Tunnel boring machines

Deep under Melbourne, tunnel boring machines (TBMs) are busy carving out tunnels, to provide more travel options to the city’s road and rail users.

What’s a TBM?

A TBM is a machine that excavates soil and rock. Victoria’s Big Build is using TBMs to dig the tunnels for the Metro Tunnel Project, the West Gate Tunnel Project and the North East Link Program.

How does a TBM work?

  1. The huge cutting head on front of the TBM rotates, with hydraulic cylinders pushing it forward from behind. Hardened cutter discs mounted on the cutting head do the actual work of breaking away the soil and rock.
  2. Conveyer belts and pipes inside the TBM take the rock and soil to the end of the machine and then to the surface.
  3. The TBM places curved pieces of concrete to make the newly dug tunnel watertight.

Our TBMs at a glance

Our largest TBMs – used to build the West Gate Tunnel – weigh around 4000 tonnes and are 15.6m in diameter.

Our longest TBMs – used for the Metro Tunnel – were 7.3m in diameter and 120m long. That’s the same as 3 E-class trams end to end.

Our machines:

  • can travel up to 10m underground each day
  • will be operating 24 hours a day, 7 days a week
  • have state-of-the-art navigation systems, to ensure the tunnel is in exactly the right location
  • make little disturbance above ground.

Smaller versions of these machines, known as mini-TBMs, have also been used to dig the tunnels needed for cables, pipes and sewers.

Working in a TBM

Highly trained specialist operators control the machines, with up to 20 crew members on board at a time.

Working so far below ground level, the team work under pressurised conditions, and need to spend up to 2 hours depressurising before returning to the surface.

As the crew works a 12-hour shift, the TBMs are even fitted out with toilets, offices and kitchens!

Tunnelling projects

Metro Tunnel

The Metro Tunnel Project‘s 4 TBMs have excavated twin 9km tunnels. These large-scale TBMs are designed to cut through material ranging from from hard basalt to softer silt.

The amount of material removed from the tunnels would fill the MCG 1.2 times.

These new tunnels will join Parkville, Arden, Town Hall, State Library and Anzac stations.

West Gate Tunnel

The West Gate Tunnel Project has 2 TBMs, 1 to excavate the 2.8km inbound tunnel and the other to excavate the 4km outbound tunnel. The outbound tunnel will take around 18 months to dig.

At its deepest point, the West Gate Tunnel will be 27.2m underground, the depth of an 8-storey building.

North East Link

North East Link Program will use TBMs to create 6.5km tunnels – the longest road tunnels in Victoria’s history.

Staying with tradition

TBMs are traditionally given female names, a custom dating back to the 1500s when workers using explosives for excavation prayed to Saint Barbara.

Our TBMs are named after these ground-breaking Victorian women:

  • Joan Kirner – First female Premier of Victoria (Metro Tunnel Project)
  • Alice Appleford – Australian nurse who served in both World Wars (Metro Tunnel Project)
  • Millie Peacock – First woman elected to the Parliament of Victoria (Metro Tunnel Project)
  • Meg Lanning – Captain of the Australian women’s cricket team (Metro Tunnel Project)
  • Vida Goldstein – Campaigner for women’s voting and electoral rights (West Gate Tunnel Project)
  • Bella Guerin – First woman to graduate from a university in Australia (West Gate Tunnel Project)

Today, machines are blessed by the church alongside smoking ceremonies by traditional owners.