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Tunnel boring machines finish up on Metro Tunnel

All four tunnel boring machines (TBM) have finished digging on the Metro Tunnel Project, building two nine-kilometre-long, 6.3-metre-high rail tunnels under Melbourne’s City Loop.

TBM Millie, Alice, Joan and Meg began digging 20 months ago, lining the tunnel walls with around 250,000 tonnes of curved concrete segments to create a waterproof tunnel lining.

The machines have removed 600,000 cubic metres of rock and soil, or around one third of the total 1.8 million cubic metres to be excavated for the entire project

The TBMs have dug as deep as 40 metres below ground and tunnelled through basalt rock, gravel and silt and clay.  After starting work progressively from August 2019, the TBMs tunnelled an average of 90 metres a week, with TBM Alice recording the best rate of 195 metres in a single week.

TBM Meg arrived at the Town Hall Station site 25 metres under Swanston and Collins streets, following Millie, Joan, and Alice, which have broken through at the station over the past month.

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TBMs Joan and Meg – dug their final 670 metres under Swanston Street from the State Library Station site over the past three months. TBMs Millie and Alice – began tunnelling in December to complete their final 1.8-kilometre leg under St Kilda Road and the Yarra River.

Roadheaders will continue excavating the CBD station caverns and are digging the final section of tunnels along with the platforms at Town Hall Station.

The four TBMS will now be dismantled underground and retrieved, with the ‘skin’ of each TBM shield to remain in the tunnels to form part of the permanent lining. The remaining components will be assessed for potential reuse on other tunnelling projects.

Construction is also underway on the 26 cross passages – the short tunnels that connect the main tunnels and are an important safety feature for passengers should an incident occur.

With the tunnel entrances at South Yarra and Kensington completed, work has also begun to connect the entrance structures to the tunnels.

A range of different systems are needed, including signalling, train control, security, communications, power, and mechanical systems, as well as associated control systems.

Victorian Transport Infrastructure Minister Jacinta Allan said it is a huge milestone for the amazing team at the Metro Tunnel.

“This vital project is a year ahead of schedule but there’s still with a huge amount of work to be done to finish the stations and get the tunnel ready to deliver more trains, more often,” Allan said.

“Projects like the Metro Tunnel will connect key locations including the Parkville medical and education precinct, St Kilda Road and the Arden Precinct to the rail network for the first time and is supporting thousands of jobs.”

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