A tunnel boring machine (TBM) is 12 metres beneath the bed of the Yarra River, excavating the final few hundred metres of tunnel between South Yarra and Melbourne’s CBD.
TBM Millie, a 1100 tonne machine, is being used to dig the twin tunnels for the Melbourne Metro Tunnel project.
Tunnellers are working day and night on the massive machine, which will take around two weeks to dig 120 metres under the city’s waterway.
After crossing the river, TBM Millie will dig a further 300 metres to Town Hall Station below Swanston Street to complete the final section of tunnel in the south-east, followed a few weeks later by TBM Alice.
Geological and environmental testing has shown that ground conditions deep under the Yarra River include silt, gravel and basalt. The Metro Tunnel TBMs have encountered a variety of ground conditions when tunnelling in other sections of the project.
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“Tunnelling on the Metro Tunnel Project is heading into its final stages, with a TBM now digging under the Yarra, as it completes this incredible feat of engineering deep under Melbourne’s CBD,” Transport Infrastructure Minister Jacinta Allan said.
“We’ve almost got 18 kilometres of concrete-lined tunnel, while five new stations are taking shape underground with walls, roofs and platforms now being built – as we continue on the path to more trains, more often.”
Tunnelling is now around 85 per cent completed, with TBM Joan now digging more than 30 metres below Swanston Street towards Town Hall Station from the State Library Station site in the CBD’s north, and TBM Meg to be launched in coming days.
The arrival of all four TBMs at Town Hall Station later this year will mark the end of tunnelling to create the twin nine-kilometre-long, 6.3-metre-high rail tunnels from Kensington under the Melbourne CBD to South Yarra.
Each 120-metre-long TBM is equipped with an advanced navigation system to ensure they dig accurately along the tunnel alignments. They are staffed and monitored 24 hours a day, seven days a week, and equipped with an office, kitchen and toilets.
The Metro Tunnel will have two CBD stations – Town Hall Station at the southern end of Swanston Street and State Library Station at the northern end of Swanston Street. These will allow passengers to connect to City Loop services via underground pedestrian links at Flinders Street and Melbourne Central stations.
Measuring in at 19 metres wide, the Town Hall and State Library station platforms will be among the widest underground metro platforms in the world.