A tunnel boring machine (TBM) is the machine used to excavate tunnels. TBMs can bore through a variety of ground conditions, from hard rock to sand.
About the Metro Tunnel TBMs
Four TBMs were used to create the Metro Tunnel's twin 9km tunnels. Each TBM was 7.28m in diameter, weighed more than 1100 tonnes and reached 120m in length.
The heaviest component was the cutterhead, which weighed 100 tonnes and acted as a drill that can tunnel through rock six times harder than concrete. The face of the cutterhead was 7.28m in diameter.
A crew of up to 10 people, including a TBM operator, worked on each TBM at any one time. The TBMs were staffed and monitored 24 hours a day, 7 days a week, and came fully equipped with facilities for our workers, including an office, kitchen and toilets.
They were equipped with a state-of-the-art navigation system that ensured they dug accurately along the tunnel alignments.
The Metro Tunnel Project used 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 was mixed with slurry and transported back to the above-ground slurry treatment plant. The excavated material was then separated from the slurry and transported to a disposal site.
The TBMs were 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.
Tunnelling journey
TBM Joan
- September 2019 to February 2020: Arden to Kensington, westbound tunnel
- May 2020 to August 2020: Arden to Parkville, eastbound tunnel
- October 2020 to December 2020: Parkville to State Library, eastbound tunnel
- February 2021 to April 2021: State Library to Town Hall, eastbound tunnel
TBM Meg
- October 2019 to March 2020: Arden to Kensington, eastbound tunnel
- June 2020 to September 2020: Arden to Parkville, westbound tunnel
- November 2020 to February 2021: Parkville to State Library, westbound tunnel
- March 2021 to May 2021: State Library to Town Hall, westbound tunnel
TBM Millie
- April 2020 to September 2020: Anzac to South Yarra, eastbound tunnel
- December 2020 to March 2021: Anzac to Town Hall, westbound tunnel
TBM Alice
- May 2020 to October 2020: Anzac to South Yarra, westbound tunnel
- January 2021 to May 2021:Anzac to Town Hall, eastbound tunnel
Arden to Parkville
Watch our Construction Manager Bored Tunnels – West, Adam Gorny, provide a general overview about tunnelling from Arden to Parkville.
Domain to South Yarra
Watch our Construction Manager Bored Tunnels – East, Andreas Mindt, provide a general overview about tunnelling from Domain to South Yarra.
Explaining the tunnelling process
In August 2019, as Joan the TBM prepared to launch towards Kensington, our Director of Tunnels and Underground Stations explained how tunnelling operations would take place on the Metro Tunnel Project.
Environmental management
Watch our Environment Manager, James Hamilton, provide an overview about environmental management, including noise and vibration, during tunnelling.
Our TBM names
Per tradition, each of the TBMs were given a name. They were each also assigned a different colour. Read on to learn about the women who inspired our naming choices.
Joan
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
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
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
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.