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After taking a temporary lift about 30 metres down a shaft, construction workers descend a set of stairs before an underground world opens up. In front of them, the longest cavern to be built for any of Sydney’s three new metro rail lines disappears into the distance beneath Pyrmont on the western edge of the CBD.
Carved out of sandstone, the cavern extends for a staggering 320 metres, comprising a 180-metre stretch for station platforms, and 140 metres for a crossover section where trains will be able to switch tracks on the $25.5 billion Metro West rail line between the CBD and Parramatta. Above ground, people walk city streets oblivious to what is happening under their feet.
At the western end of the cavern, two giant tunnelling machines named Jessie and Ruby have temporarily come to rest after recently smashing through rock within five hours of each other to reach the site of the Pyrmont metro station.
Over the next few weeks, they will be pulled into the cavern for maintenance before they start worming their way under Darling Harbour in mid-August for another kilometre to their final stop beneath the CBD.
The two boring machines started their journey from the Bays precinct near Rozelle in May last year, navigating a fault line and foundations for the Anzac Bridge on their journey to Pyrmont. They have been slicing through rock at a third of the pace of other boring machines working on Metro West because of the combination of hard and soft rock under the harbour, which is one of the most complex parts of the project.
Sydney Metro chief executive Peter Regan said the two under-harbour crossings from the Bays precinct to the CBD via Pyrmont were challenging and required extra care during the excavation.
“The tunnel boring machines that are being used here are high-pressure slurry machines, which allows them to go under the water. That’s a slower process, and there’s been a very cautious approach,” he said.
They are expected to reach a giant cavern for the easternmost station on the Metro West line, beneath Hunter Street in the CBD, by the end of the year. By then, they will have excavated twin 2.3-kilometre tunnels from the Bays precinct to the northern end of the CBD, removing 460,000 tonnes of spoil.
“There’s a fair way to go, but the route is known,” Regan said. “It will be very careful [tunnelling], under the harbour in particular, and then under the city, where you’ve got so many buildings.”
At Pyrmont, contractors have had to operate within a tight space above ground, where they dug a shaft to allow excavation of the cavern that is about 18 metres tall and 23 metres wide.
“It’s a very tight site compared to some of the other sites that we’ve operated on,” Regan said. “Pyrmont is a dense area, and there’s a lot of activity. There’s also a lot of residential, so it has been quite a challenge.”
Regan said the Pyrmont station would most closely resemble Victoria Cross station at North Sydney, which opened last August as part of the second stage of the M1 line. When it opens in 2032, the Metro West line will stretch underground for 24 kilometres between the CBD and Westmead, near Parramatta. The line is the fourth and largest stage of Sydney’s metro network, which is one of the world’s biggest rail projects, costing $65 billion.
Transport Minister John Graham said the new metro station would turn Pyrmont into one of the most connected suburbs in the country, allowing people to reach the CBD within just two minutes by train.
“Multiple transport links here will really make this a big part of the CBD. That’s really good for housing; it’s really good for jobs in this area. [It will] allow the CBD of Sydney to expand ... as Pyrmont becomes a super-connected suburb,” he said.
A 31-storey tower will also be built above the Pyrmont station, comprising 160 apartments and five levels of offices and shops.
So far, the Metro West project is about 85 per cent of the way through tunnelling. At the far western end, tunnel boring machines are due to reach Westmead by the end of the year.
“This is incredible engineering,” Graham said. “One of the remarkable things about these sites is you can walk right across this at street level and never know what’s going on underground.”
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