Digging done for Metro Tunnel mega machines


Four huge tunnel boring machines (TBMs) have finished 20 months of digging under Melbourne to create two nine-kilometre-long rail tunnels for the Metro Tunnel Project.

The incredible feat of engineering included tunnelling just 1.5m underneath the City Loop as trains continued to run, as well as digging 12 metres under the Yarra and seven metres below the Burnley Tunnel.

TBM Meg recently arrived at the Town Hall Station site 25 metres under Swanston and Collins streets, following the breakthroughs of Millie, Joan and Alice.

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

It’s been a huge undertaking for the four machines, which have tunnelled on six separate legs between Kensington and South Yarra, installing more than 55,000 curved concrete segments to create a waterproof tunnel lining.

The TBMs have dug as deep as 40 metres below ground (under the northern end of Swanston St) 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.

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 – enough to fill the MCG 1.2 times.

While the TBMs have finished the rail tunnels between the project’s five stations, road headers – huge digging machines excavating the CBD station caverns – are still at work digging the final section of tunnels alongside the platforms at Town Hall Station.

With their work in Melbourne finished, the four TBMs are being 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.

Minister for Transport Infrastructure Jacinta Allan said, “The Metro Tunnel will connect key locations including the Parkville medical and education precinct, St Kilda Rd and the Arden Precinct to the rail network for the first time and is supporting thousands of jobs.”

Work on the Metro Tunnel and other critical infrastructure projects has continued during restrictions. To ensure the safety of all workers and the community, all work undertaken operates under a COVID-safe plan •

For more information visit: metrotunnel.vic.gov.au

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