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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 overseas, before being disassembled and shipped to Melbourne in sections. When the TBMs arrive, the sections are transported from the Port of Melbourne to the St Kilda Road precinct and North Melbourne, where they are reassembled on site, ready to start tunnelling.

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

How will they be named?

The TBMs that will carve out the Metro Tunnel Project are arriving soon, and it seems fitting they should be named after figures – past and present, high-profile and quiet achievers – who have made a similarly noteworthy impact.

We want to name our TBMs after ground-breaking women – and we want you to be involved. Visit the Big Build website, submit your suggestion and have a chance to win a VIP TBM experience.

The competition closes on 7 October 2018.

You can also visit a two-metre replica of a TBM at Metro Tunnel HQ, our visitor centre located at 125-133 Swanston Street, Melbourne.

Why are they named after women?

According to tunnelling tradition, TBMs are given female names as a sign of good luck for the project ahead.

The origins of this can be traced back hundreds of years to when miners and military engineers began working with explosives, which were often used to tunnel in those times.

They would pray to Saint Barbara – patron saint of tunnellers, as well as military engineers – for protection. According to the legend, Barbara lived in the third century near what is now Istanbul, Turkey and took refuge with silver miners to avoid persecution.

London’s Crossrail project followed this tradition, and its TBM names included ‘Phyllis and Ada’. This machinery was named after Phyllis Pearsall, who created the London A-Z map, and Ada Lovelace, who was one of the earliest computer scientists.

There are parallels with other industries, such as the maritime world, where ships may be given various names but are commonly referred to as “she”. One possible explanation is because early ships were dedicated to a goddess; and when belief in goddesses waned, ships were named after important mortal women.

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 pipes running through and behind the TBM.
  • Progressively installing curved concrete segments to create a watertight lining inside the tunnels.

The Metro Tunnel TBMs will work more than 40 metres underground at their deepest point 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 North Melbourne 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 Anzac Station site on St Kilda Road and supported by a work site at Edmund Herring Oval. A TBM site will be located in South Yarra 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 North Melbourne and the St Kilda Road precinct.

Construction process

For the western half of the project:

  • Two TBMs will be launched at the site of the new North Melbourne Station and will travel towards Kensington.
  • They will be retrieved at the western tunnel entrance and taken back to North Melbourne, 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 State Library Station.
  • When they reach State Library Station, they will be recovered back through the tunnels to Parkville where they will be extracted.

For the eastern half of the project:

  • Two TBMs will be launched at the site of Anzac Station and will travel towards South Yarra.
  • They will be retrieved at the eastern tunnel entrance and taken back to the St Kilda Road precinct, where they will be relaunched to travel towards Town Hall Station.
  • When they reach Town Hall Station, they will be recovered back through the tunnels to Anzac Station where they will be extracted.