Guide to tunnelling

There is nothing simple about the construction of a tunnel. It’s a process of problem solving and discovery considered to be one of the most complex civil engineering challenges to solve.

The stars of the show are two kinds of machine – Roadheaders and Tunnel Boring Machines. Each is suited to different type of work, but both will need to work hard to get through the different soild and hard rock types under our busy city.

diagram showing the path of the new tunnell and a 3D model of how it sits underground
Tunnel Boring Machines

Tunnel Boring Machines

Two TBMs will head north from Woolloongabba, breaking through into the station caverns at Albert Street, Roma Street and then finally at the northern portal.

diagram of how the tunnel segments are put together.

Tunnel lining

As a TBM moves along it lines each tunnel with strong concrete rings, made of interlocking segments.

a diagram of a roadheader.

Roadheaders

These electrically powered tunnelling machines perform the finely-controlled digging needed for station cavern excavation and for the tunnelling from Woolloongabba to Boggo Road.

 Tunnel Boring Machines

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. Now that they have arrived in Queensland, these machines will be retrofitted and refurbished in Brisbane in order to prepare them for digging Brisbane’s first underground.

The TBMs will be launched from the Woolloongabba station site and will dig a tunnel each under the Brisbane River to the Albert Street station. They will then continue to the new Roma Street station before emerging at the project’s northern portal at Normanby.

TBMs Fast Facts

  • The two TBMs are being used each weighing 1350 tonnes with a crew of up to 15 people working in the TBM at any one time
  • The TBMs are expected to travel 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 will generate 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

Tunnel Lining

The tunnel will be lined with strong concrete rings, made up of six locking segments connected by dowels. The TBM installs the segments as it moves along the tunnel.

Work has begun at Wacol to produce 25,000 concrete tunnel segments that will be needed to make the 2150 rings per tunnel.

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 will be produced at Wacol
  • Each segment is 27 centimetres thick and 1.7 metres long
  • One truck can only carry six segments at a time
  • Once in production, the facility will produce 140 segments per day
  • More than 105,000 cubic metres of concrete will be used to create the segments

  Roadheaders

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 will be used to build Cross River Rails tunnels and stations