Construction of a 24km underground rail link in Sydney has reached a milestone with arrival of two tunnel boring machines (TBMs) at the city's Olympic Park.

The machines, named Betty and Dorothy, completed their 4.6km journey from the Clyde Stabling and Maintenance Facility site ten months ago.

They have excavated approximately 857,500t of material and installed more than 32,600 concrete precast segments along the way.

While Betty has been disassembled and returned to Clyde, Dorothy is in the midst of this process, and both will be relaunched in the opposite direction towards Westmead.

The work forms part of the Sydney Metro West project to link the western suburb of Parramatta with the city's central business district (CBD).

The focus at Sydney Olympic Park will shift to the opposite end of the 200m long, 37m wide, 27m deep station box, where TBMs Beatrice and Daphne are due to breakthrough later this year.

These machines, which are building a 11km section of the line from The Bays, have recently relaunched from North Strathfield. They have another 2km of tunnel to build before reaching the Olympic Park.

The project’s newest addition, TBM Jessie, is tunnelling from The Bays towards the Sydney CBD. It has excavated 230m of tunnel since its launch in May.

Meanwhile the project's final TBM is expected to begin the second under-harbour tunnel later this year.

Acciona Construction Australia Pty Ltd and Ferrovial Construction (Australia) are delivering the section from The Bays to the Olympic Park under a A$2bn (£1bn) deal.

John Holland, CPB Contractors and Ghella secured the Eastern Tunnelling Package, which includes the 3.5km stretch from the CBD to The Bays. It was awarded the contract by client New South Wales Government in November 2022.

The Gamuda Australia and Laing O’Rourke Consortium was awarded the A$2.2bn Western Tunnelling contract to deliver 9km from the Olympic Park to Westmead.

Sydney Metro West will double rail capacity between Greater Parramatta and the Sydney CBD.

Elsewhere in the city, a 23km railway is being constructed to link the new Western Sydney International Airport to the rest of the city's public transport system. Tunnelling on the Sydney Metro – Western Sydney Airport line has now been completed, with the last of the project's four mega TBMs breaking through in June this year.