Big enough for 30,000 elephants, major Sydney metro station reaches milestone

A shrine to Saint Barbara, patron saint of tunnellers and engineers, stands at the entrance to Australia’s largest underground rail cavern, scooped from sandstone beneath Sydney’s city centre.

The saint watched over a single road header and 57 workers who excavated 241,000 tonnes of rock to create an underground cathedral-like space for the flagship Hunter Street station on the $25 billion Metro West rail line between the CBD and Parramatta.

The cavern has been carved beneath the office blocks and busy streets of the northern end of Sydney’s CBD.Credit: Nick Moir

“[That’s] the equivalent of 290 Olympic-sized swimming pools, about 30,000 elephants and about 275,000 moderately sized dogs,” Premier Chris Minns said during a site visit on Wednesday.

“The scale of it is incredible.”

Minns’ visit marked the completion of 20 months of work to dig the gargantuan cavern, which measures 180 metres long, 28 metres wide and 20 metres from the floor to the crown of the roof.

The Hunter Street station is one of the most complex parts of the Metro West project, requiring meticulous work to dodge surrounding rail tunnels, basements for high-rise office towers and the heritage-listed State Library on nearby Macquarie Street. The cavern passes 1.8 metres beneath tunnels for the M1 metro line, which runs in a north-south direction under the centre of the city.

Parts of the cavern are eight metres beneath the Sydney Tank Stream, and 21.5 metres below the City Circle train line. It’s also near a tunnel full of high-voltage cables that power part of the CBD.

The station’s location meant it had to be designed to withstand enormous loads. About 3000 cable bolts – each about eight metres long – were driven into the cavern’s walls and tensioned to pull up the rock, effectively forming strengthened beams. The bolts were invented decades ago for the Snowy Hydro project.

Minns said of the project: “It’s often dangerous work and the logistical challenges of having a major construction project in the middle of one of the busiest cities in the world is incredibly difficult.

“Weaving winding metro tunnels around other metro tunnels, as well as icons like the State Library, is not an easy task, that’s why we need brilliant engineers, and they’ve done an incredible job.”

Transport Minister John Graham tours the underground cavern to mark the completion of excavation works on Wednesday. Credit: Nick Moir

The station will be the sole CBD stop on the 24-kilometre Metro West line, which the government says will double rail capacity between Parramatta and Sydney’s city centre when it opens in 2032.

It is expected to handle 10,000 people an hour during the morning peak by 2036, via entrances on George, Bligh and O’Connell streets, making the station the busiest on Sydney’s metro network.

Transport Minister John Graham said the completion of the Hunter Street cavern was “a big step forward on the Metro West project”. “It’s incredibly complex work right in the heart of the city.”

Minns said the future metro line would change the way people moved around the city, but it would also complement the government’s push to build more high-density housing within established suburbs.

“These are city-changing projects. They’re expensive, and they take a lot of time, but they’re absolutely essential if we’re going to grow in the years ahead,” Minns said.

Saint Barbara, who is patron saint of tunnellers and engineers, has watched over excavation of the subterranean cathedral-like cavern.Credit: Nick Moir

At the cavern’s western end, two giant holes have been scraped out for a pair of boring machines. The metro station will eventually be topped by a development of two towers comprising offices, bars, restaurants and shops to form one of the most significant developments in the city centre this decade.

Pub and restaurant baron Justin Hemmes is part of a consortium competing against a group led by global investment giant Brookfield for the right to complete the metro station and build the towers of 51 and 58 storeys. The government expects to announce the successful tenderer later this year.

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