Guide to tunnelling

Tunnel Boring Machines (TBMs) are like underground factories. 165 metres long, they can both tunnel and precisely install concrete reinforcing segments at the same time.

As part of our commitment to sustainability, both of these machines were used on the Sydney Metro project. After they arrived in Queensland, the machines were retrofitted and refurbished in Brisbane in order to prepare them for digging Brisbane’s first underground.

TBMs are traditionally named after women, stemming from a long-standing tradition dating back to the 1500s when miners prayed to their patron saint, Saint Barbara, to protect them underground.

Our TBMs were named after two ground-breaking Queensland women, in honour of their outstanding contributions to the state. The first TBM launched was named ‘Else’ after trailblazing engineer Else Shepherd AM, while the second TBM launched was named ‘Merle’ in honour of pioneering feminist Merle Thornton AM. You can read more about the choice of names for the TBMs here.

Else and Merle commenced tunnelling in February and March 2021 respectively. They were launched from the Woolloongabba station site to dig a tunnel each under the Brisbane River to our Albert Street station. They then continued to the new Roma Street station before both emerged from the project’s northern portal at Normanby in December 2021

TBMs Fast Facts

• The two TBMs used each weigh 1350 tonnes with a crew of up to 15 people working in the TBM at any one time
• The TBMs travelled approximately up to 30 metres per day, operating 24 hours a day, seven days a week
• The front of the TBM is called the ‘cutterhead’ which acts as a drill that can tunnel through rock harder than concrete
• The cutter head measures 7.2 metres in diameter
• The TBMs generated 290,000 cubic metres of spoil as they make way for the twin Cross River Rail tunnels
• Each TBM is fully equipped with kitchen facilities, offices and toilets

Track our TBMs

You can chart the journeys made by our two TBMs – Else and Merle – on our TBM Tracker as they tunnelled from Woolloongabba to Albert Street, before continuing to Roma Street and emerging at the project’s northern portal at Normanby.

The tunnel is lined with strong concrete rings, made up of six locking segments connected by dowels. A TBM installs the segments as it moves along the tunnel. This is followed by the installation of ground support techniques such as inserted rock bolts (metal rods) and concrete which is sprayed on the tunnel lining for strength.

Precast concrete segment fast facts:

• Six concrete segments are used to create one tunnel ring
• 4,157 tunnel rings are required to line both tunnels
• 25,000 segments were produced at Wacol
• The facility produced 140 segments per day
• Each segment is 27 centimetres thick and 1.7 metres long
• More than 105,000 cubic metres of concrete was used to create the segments

These electrically powered tunnelling machines perform the finely-controlled digging needed for shallow tunnel, escape passage and station cavern excavation.

Roadheaders use their rotating excavating head with metal picks to cut rock. An Operator controls the machine from inside the cabin, while a Cable Spotter assists in moving the machine safely.

Roadheader fast facts

• A roadheader is 25 metres long end to end and weighs 115 tonnes.
• They are able to excavate 60 tonnes of rock per hour
• A roadheader’s cone, or ‘pineapple’, will wear away more than 30 picks during an 8 hour shift .
• Roadheaders usually travel 1-5m in 24 hrs
• A total of six roadheaders were used to build Cross River Rails tunnels and stations