Tunnel Boring Machines
Tunnel boring machines (TBMs) are large machines that excavate below the ground surface, while simultaneously installing concrete lining units (segments) to build a tunnel. Two TBMs have been specifically designed for the METRONET Forrestfield-Airport Link by German company Herrenknecht, the world’s leading supplier of TBMs.
Despite their huge electric and hydraulic-powered motor drives, TBMs create little noise at the surface and cause only minor vibrations as they cut through the soil and rock in their path.
There are various types of TBMs to cater for different ground conditions and project requirements. For this project, the TBMs are Mixshield which use the latest dual-mode technology capable of adapting to variable ground conditions (such as sand, rock and clay) as the machine progresses.
Key components for our TBMs were manufactured in various places around the world before an in-depth nine-month assembly and testing program was conducted in China. Once testing was finished, they were disassembled and shipped to Henderson Port. The TBMs were then transported to site, reassembled and lowered into the dive structure at High Wycombe, where they tunnelled between High Wycombe and Bayswater between July 2017 and April 2020.
During their 8km journeys the TBMs excavated under Perth Airport and the Swan River, reaching up to 26m depth below the surface.
To find out more about how these machines operate, view the TBM fact sheet or the TBM animation.
As at 9am, Wednesday April 22, 2020:
||Number of tunnel rings installed
| TBM Grace
| TBM Sandy
Naming the TBMs
Like ships, TBMs are named before they begin work to bring good luck. Traditionally, a TBM cannot start work until it is given a name. TBMs are generally given female names as underground workers look to Saint Barbara for protection.
Our first TBM was named Grace, in honour of pre-primary student Grace McPhee who was nominated by her classmates at Edney Primary School in High Wycombe. The students said Grace, who is undergoing treatment for leukaemia, was the toughest person they knew – a toughness the TBM would need to bore through the earth. This TBM was decorated with artwork by Year 6 Walliston Primary School student Georgia Fields.
Our second TBM was named Sandy as suggested by High Wycombe Primary School Year 4 student Sarah Spratt. Sarah was inspired after finding a sandgroper in her backyard, as the local insect (which is also a colloquial name for Western Australians) is 'excellent at tunnelling, just like the TBM'. This TBM was decorated with artwork by Rossmoyne Primary School Year 5 students Faith Brand and Jood Al Jashammi.