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Metro Tunnel

Tunnel Boring Machines

Tunnel Boring Machines (TBMs) will be used to build the Metro Tunnel.

TBMs are large machines that tunnel through ground, progressively installing concrete linings to support the excavated tunnel. Excavated material is transported through the machine to the surface for removal by trucks.

TBMs are typically used in the construction of long underground tunnels. They are tailored for specific ground conditions and are more than 100 metres long and weigh up to 1,000 tonnes.

Metro Tunnel's TBMs will be built and tested in Europe, before being disassembled and shipped to Melbourne in segments. When the TBMs arrive, the segments are transported from the Port of Melbourne to Domain and Arden, where they are reassembled on site, ready to start tunnelling.

The Metro Tunnel TBMs will build tunnels approximately seven metres in diameter.

How do they work?

TBMs perform two main tasks:

  • excavating rock and soil with a rotating cutter head at the front of the machine before it is transported via a conveyor belt or pipes running through and behind the TBM
  • progressively lining the tunnels with pre-cast concrete segments from within the TBM to support the ground and minimise groundwater seepage into the tunnel.

The Metro Tunnel can work more than 40 metres underground and will operate on a 24/7 basis.

TBM cross section

Launch shafts

At the start of the process, a deep launch shaft is dug from the surface to where the TBM needs to start tunnelling. The TBM is then lowered by crane into the shaft in sections and assembled before it begins excavating towards a station or tunnel entrance. It is then 'pulled' through an excavated station box to begin excavating the next section of tunnel, or extracted via a retrieval shaft and taken back to a launch shaft to start digging another section.

The TBM launch shaft for the western section of the project will be located at the Arden Station site, with a TBM retrieval site in Kensington near the western tunnel entrance.

For the eastern section of the project, the TBM launch shaft will be located at the Domain Station site on St Kilda Road and supported by a work site at Edmund Herring Oval. A TBM retrieval site will be located near the eastern tunnel entrance.
A range of activities need to take place around the TBM launch shafts to support tunnelling operations. These include site facilities, the processing and management of excavated material prior to disposal, as well as storage of the concrete segments used to line the tunnels.

The concrete segments will be manufactured at an off-site plant and then transported to Arden and Domain.

Construction process

For the western half of the project:

  • Two TBMs will be launched at Arden and will travel towards Kensington
  • They will be retrieved at the western tunnel entrance and taken back to Arden, where they will be relaunched to travel towards Parkville Station.
  • When the TBMs arrive at Parkville they will be pulled through the excavated station box to continue their journey towards the new CBD North Station.
  • When they reach CBD North, they will be recovered back through to tunnels to Parkville where they will be extracted.

For the eastern half of the project:

  • Two TBMs will be launched at Domain and will travel towards South Yarra
  • They will be retrieved at the eastern tunnel entrance and taken back to Domain, where they will be relaunched to travel towards CBD South Station.
  • When they reach CBD South, they will be recovered back through to tunnels to Domain where they will be extracted.