Tunnel boring machines

A tunnel boring machine (TBM) is a machine used to excavate and construct long tunnels in varying ground conditions. The type of TBM selected is dependent on the ground conditions of the tunnel alignment.

Transcity will use two Herrenknecht Double Shield TBMs to excavate Legacy Way’s two 4.6 kilometre tunnels. These machines have been selected as they are well suited for the excavation of long tunnels in hard rock.

Each of the 2,800 tonne TBMs have been recycled from parts of the TBMs used on CLEM7, which resulted in significant savings to the project. Both TBMs have been completely restored and modified to suit the construction conditions of Legacy Way.

Each TBM is assembled within a custom-built TBM ‘launch box’ at the project’s western worksite in Toowong. It will take approximately three months for the project to assemble the 50 large steel segments of the TBM, including the cutter head, which is 12.4 metres in diameter. These various segments will be delivered to site and lowered into the launch box by three overhead cranes.

Legacy Ways TBMs have been named to acknowledge both our war heroes and the ongoing support of Legacy for Australian Defence families.

The first TBM – Annabell – is named after Annabell MacKinney, the daughter of the late Lance Corporal Jared MacKinney who was killed in action in Afghanistan in 2010. She is also the youngest person in Legacy’s care. The second TBM – Joyce – is named after Joyce Tweddell, a nurse during World War II who showed immense courage after being held as a prisoner of war in Sumatra for three years before going on to become Queensland’s Chief Radiographer.

Once Legacy Way opens, Brisbane City Council will donate one cent from each toll to Legacy, which is expected to raise $600,000 in the first five years of operation.

How does a Double Shield TBM work?

A Double Shield TBM is a custom-built machine which simultaneously excavates and lines the tunnel, while removing the excavated material from the tunnelling area.

The front section of the TBM contains a forward moving shield which allows for excavation while the rear section remains stationary as the concrete segments, which form the tunnel walls, are installed.

The excavated rock, or spoil, is passed through the machine, onto an underground conveyor belt and transported to the Mount Coot-tha quarry.

For more information, check out the tunnel boring machine fact sheet.