For the first time in Australian history, three large-scale tunnel boring machines are tunnelling simultaneously on the same underground road project — and it is happening beneath Adelaide.
The milestone has been reached on the $15.4 billion River Torrens to Darlington (T2D) project, with all three of its giant tunnel boring machines (TBMs), Mary, Catherine and Elizabeth, now excavating their way beneath the city.
It marks a major step forward for South Australia’s biggest-ever infrastructure project, which will complete the final 10.5-kilometre section of the North-South Corridor and ultimately create 78 kilometres of non-stop, traffic light-free motorway between Gawler and Old Noarlunga.
“For the first time in Australian history, three large-scale TBMs are tunnelling at the same time on an underground road project, and it’s happening right here in South Australia,” Infrastructure and Transport Minister Joe Szakacs said.
“Mary, Catherine and Elizabeth will now work in concert underneath Adelaide to deliver a non-stop South Road.”
The scale of the machinery involved is enormous. Each TBM weighs around 3,500 tonnes and features a 15-metre-high, 300-tonne cutterhead equipped with 82 cutting discs weighing up to 350 kilograms each, as well as almost 200 teeth.
Once the machines are fully up and running, they are expected to excavate around eight to 10 metres each day.
For now, crews are gradually ramping up operations while closely monitoring the machines and adjusting cutterhead rotation speed, penetration rate and thrust force depending on the ground conditions encountered.
Even the individual cutting tools require close attention. Specially trained workers regularly inspect the teeth and discs for wear, undergoing specialist hyperbaric training so they can safely enter the pressurised environment behind the cutterhead.
As the three machines push forward, an equally significant operation is happening in the opposite direction.
Rock and soil excavated by the TBMs, known as spoil, is carried by conveyor to a spoil shed before being loaded into covered trucks and transported to a re-use site at Gillman.
Around 7.5 million tonnes of spoil is expected to be generated across the entire T2D project, including approximately five million tonnes from tunnelling and another 2.5 million tonnes from civil works.
Running three large-scale TBMs at once allows work on the Northern and Southern Tunnels to happen concurrently, with tunnelling across the project expected to take up to 24 months.
Federal Infrastructure, Transport, Regional Development and Local Government Minister Catherine King said the latest milestone brought the project another step closer to completing Adelaide’s North-South Corridor.
“The Albanese Government is proud to partner with the South Australian Government to improve safety, connectivity and productivity from Gawler to Old Noarlunga,” Minister King said.
While the machines disappearing beneath Adelaide are among the project’s most visible milestones, their eventual breakthrough won’t mark the end of construction.
Crews will still need to build the roads inside the tunnels, install mechanical, electrical and safety systems and undertake extensive testing, commissioning and compliance work.
The project is expected to support around 5,500 jobs each year during its main construction phase.
The T2D project is jointly funded by the Federal and South Australian governments, which have each committed $7.7 billion, with the completed non-stop South Road scheduled for 2031.
