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 Forrestfield-Airport Link by German company Herrenknecht, the world’s leading supplier of TBMs.
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 Forrestfield, where they began their journey towards Bayswater in 2017.
During their 8km journey, the TBMs will excavate 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.
As at 8.30am, Thursday 18 April, 2019:
||Number of tunnel rings installed
| TBM Grace
|| Tunnelling underneath Brearley Avenue.
| TBM Sandy
|| Tunnelling underneath Woods Road.
TBMs back on track after stoppage due to mechanical issue
On Friday January 18, workers operating TBM Grace reported a potential mechanical issue with the machine. Tunnelling experts from SI-NRW and German TBM manufacturer Herrenknecht were able to identify and isolate the issue – damage to the screw conveyor, which moves excavated material away from the front of the TBM – and repair works were undertaken.
Repairs included replacing a 3m section of the 16m-long screw conveyor and repairing cracks that had been identified.
TBM Grace was restarted on Tuesday March 26 and is expected to reach Redcliffe Station in the coming months.
On Monday February 4, TBM Sandy was stopped as a precaution so that the machine’s screw conveyor could be proactively inspected for similar faults. Inspections confirmed the presence of cracks and a damage assessment took place. Repairs were completed and the machine was restarted on Tuesday April 16.
Two new screw conveyors have been manufactured by Herrenknecht and will be installed while the TBMs are at Redcliffe Station later this year.
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 is 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 is 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.
Will I hear the 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. If you are living near the tunnel route, you’ll be given plenty of notice and information before the tunnels are bored, but most people will not notice when the boring machines are close by.