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Metro Tunnel

Introducing our TBMs

A tunnel boring machine (TBM) is a machine that is used to excavate tunnels. TBMs can bore through a variety of ground conditions, from hard rock to sand.

To construct the tunnels, the TBMs will progressively line each tunnel with curved concrete segments as they dig. The twin tunnels will comprise 56,000 individual concrete segments.

Each TBM is equipped with a state-of-the-art navigation system that will ensure they dig accurately along the tunnel alignments. They are staffed and monitored 24 hours a day, 7 days a week, and fully equipped with staff facilities, including an office, kitchen and toilets.

What type of TBMs will be used for the Metro Tunnel?

The Metro Tunnel Project will use mix shield TBMs – commonly known as slurry TBMs – that are purpose-built to suit the local ground conditions. Once the TBM's cutterhead bores through the ground, the excavated material will be mixed with slurry and transported back to the above-ground slurry treatment plant.

The excavated material is then separated from the slurry and transported to a disposal site.

What is the geology like?

The geology of the area is variable. The TBMs will be required to excavate through soft soils such as Coode Island Silt, and hard basalts under the Yarra River and in some sections of the western alignment. Many sections of the tunnel alignment feature a ‘mixed-face’ geology, which is both parts hard and soft.

How big are the TBMs?

Each TBM is 7.28 metres in diameter, weighs more than 1,100 tonnes and is 120 metres long - as long as 3 E-Class trams end-to-end.

The heaviest component is the cutterhead, which weighs 100 tonnes and acts as a drill that can tunnel through rock six times harder than concrete. The face of the cutterhead is 7.28m in diameter.

How fast do the TBMs travel?

On average the TBMs will move around 10 metres every 24 hours.

How many people will be operating each TBM?

A crew of up to 10 people, including a TBM operator, will work on the TBM at any one time.

Our TBM names


Joan Kirner was the first female Premier of Victoria (serving from 1990 to 1992) as a member of the Labor Party. She was MP for Williamstown, and while Education Minister her reforms included pioneering the Victorian Certificate of Education (VCE).


Meg Lanning captains the Australian women’s national team and the Victorian Spirit. She holds the record for the most centuries in women’s one-day internationals and was the youngest Australian (male or female) to score an international 100, when she was 18.


Alice Appleford was an Australian civilian and military nurse who took part in both World Wars. During the First World War she served in hospitals in Egypt and France and was one of only seven Australian nurses decorated with the Military Medal for Gallantry.


Millie Peacock was married to three-time Premier of Victoria Sir Alexander Peacock. After his death in 1933, she won the by-election to succeed him and became the first woman elected to the Parliament of Victoria.

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