Greater Western Sydney is now home to landmark new 9.8km twin metro railway tunnels, with major tunnelling officially complete on the Sydney Metro – Western Sydney Airport project.

The historic milestone was reached after tunnel boring machine (TBM) Marlene arrived at the St Marys Metro Station site and achieved the final tunnel breakthrough for the project.

The machines spent 14 months building two separate sets of tunnels at either end of the alignment. The job required the excavation of 1,863,460t of material, enough to fill 300 Olympic pools, and the installation of 69,966 concrete segments to line the new tunnel walls.

TBMs Marlene and Catherine carved out the 4.3km tunnels from Orchard Hills, under the M4 Motorway and the Great Western Highway to reach St Marys. TBMs Eileen and Peggy constructed the 5.5km tunnels from Airport Business Park, underneath the new Western Sydney International Airport, to Aerotropolis.

The final TBM breakthroughs occurred in quick succession:

·       TBM Catherine completed the first tunnel at the St Marys site on 20 May 2024.

·       TBM Eileen broke through at the Aerotropolis site on 29 May.

·       TBM Peggy made the penultimate breakthrough for the project and arrived at the Aerotropolis site on 7 June.

·       TBM Marlene made the final breakthrough at the St Marys site on 20 June 2024.

With tunnelling complete, the TBMs will be dismantled, washed and lifted by tower cranes onto trucks to travel to a storage location, before they are shipped back to manufacturer Herrenknecht. 

Work inside the tunnels will continue and involves completing the construction of 39 cross passages and preparing for tracklaying to begin.