Tunnel vision
The massive 100m-long and 15m-high cylindrical machines that will burrow through the earth to form the Torrens to Darlington (T2D) tunnels are set to arrive later this year.
With a crew of up to 20 onboard, these gigantic machines can chew through about 8-10m of soil and rock a day.
The T2D road project will feature two twin tunnels for north and southbound traffic.
The southern tunnels will be about 4km long, with entry and exit points at Clovelly Park and beneath the tram overpass at Glandore.
To the north, the 2.2km-long tunnels will have an entry and exit point near James Congdon Drive, and another near the Brickworks shopping centre.
The maximum depth from the ground surface to the top of the tunnel will be 25m, with a further 10m to the tunnels’ road surface.
There’ll be three lanes in each direction and a speed limit of 80km/h.
The machines
The State Government has ordered three mighty tunnel boring machines (TBMs) from the German company Herrenknecht to undertake the bulk of the work.
As a TBM grinds out a tunnel, it installs prefabricated concrete lining segments that form the tunnel wall. Specialised 27m-long, multi-service vehicles (MSV) will resupply TBMs with extra segments and other material. These vehicles have driving controls at both ends like a tram.
Two smaller, 4m-diameter machines have been ordered to create passages between the twin tunnels at 120m intervals. These cross-passages can be used by workers and emergency services, if needed, and will be part of the completed tunnels’ safety systems.
One more of these smaller machines might be purchased at a later date.
The TBMs will be launched from work sites known as laydown areas, which will be located at the southern end of each twin tunnel section. New local substations will be built to power the TBMs and provide electricity for the completed tunnels.
The spoils
Excavated dirt and rock, known as spoil, is removed from the tunnel by conveyor belt to a spoil shed in the laydown area at the surface. Here it’s sorted and classified before being transported by covered trucks to spoil reuse sites.
When
The TBM components should start arriving later this year, and it’ll take several months to assemble and prepare the machines for operation. Tunnelling is expected to start in the second half of 2026 and the project is due for completion in 2031.