CONSTRUCTION of the five-station Melbourne metro project has passed a milestone with the completion of boring of the two 9km tunnels.

The work required one of the new tunnels to pass just 1.5m beneath the existing City Loop line as trains continued to run, as well as boring 12m under the Yarra riverbed and around 7m below the Burnley tunnel.

Tunnel boring machine (TBM) Meg arrived at the Town Hall Station site 25m under Swanston and Collins streets, following Millie, Joan, and Alice, which broke through at the station over the past month. TBMs Millie and Alice began tunnelling in December to complete their final 1.8km leg under St Kilda Road and the Yarra River.

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

The machines have removed 600,000m3 of rock and soil, or around one third of the total 1.8 million m3 to be excavated for the entire project.

While the TBMs have finished the rail tunnels between the five stations, excavation for the city centre stations is still in progress.

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.

The metro tunnel will transform Melbourne’s rail network, deliver more trains to and from the suburbs and cut travel times by up to 50 minutes a day.

State minister for transport infrastructure, Ms Jacinta Allan, says the $A 14bn ($US 10.8bn) project is a year ahead of schedule. The project is being undertaken by a consortium comprising Lendlease, John Holland, Bouygues Construction, John Laing, and Capella Capital.

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