This was published 7 months ago
How an underground marvel will reshape the way Sydney moves
The number of train passengers a metro station carved out beneath the central city has been built to handle is staggering.
Entering Sydney’s largest underground rail cavern, you are struck by a mass of blue-coloured waterproof lining that covers its walls and ceiling. At 28 metres wide and 180 metres long, the size of the cavern built beneath the northern end of central Sydney for the $25.3 billion Metro West line is breathtaking.
Yet what is not obvious is how close it comes to buildings, existing rail tunnels and critical power cables for the CBD. Illustrating the challenge for contractors, the top of the cavern sits just six metres below the foundations of a 169-year-old heritage hotel built from sandstone.
Once opened in 2032, the Hunter Street metro station will become the hub for train travel in and out of the northern part of the CBD. It will connect existing heavy rail and metro stations at Martin Place to Wynyard, allowing people to switch between multiple lines without setting foot above ground.
It will be bigger than both Victoria Cross station in North Sydney and the Martin Place metro station, which is the busiest on the M1 line between the city’s north-west and Sydenham.
The reason for its size is simple. While it is forecast to handle 10,000 passengers an hour when it opens in 2032, the only station in the CBD for Metro West is being built for a staggering 40,000 people an hour.
Sydney Metro chief executive Peter Regan said the station was being built to be bigger than others to cater for the “very large volume of people” entering and exiting at the same time, and major growth over coming decades.
“The complexity of what you’re seeing down in that cavern is like nothing we’ve done before in terms of the scale of what is being built under the city. It will become the biggest rail cavern in Australia,” he said. “Hunter Street will be a very busy station because it’s the end of the line, and it’s the only station in the CBD [for Metro West].”
In comparison, the M1 line has four stations in the central city – Barangaroo, Martin Place, Gadigal and Central – which means passenger loads during the peak periods are spread, instead of concentrated on one.
Initially, six-carriage driverless trains will run on the 24-kilometre line between Parramatta and the CBD every four minutes in each direction. However, the 180-metre-long stations on the Metro West line allow for trains as long as eight carriages to eventually be operated. “It’s designed very much to grow as a station,” Regan said.
Hunter and Pyrmont stations construction manager Dave Maytom said one of the challenges was the wide span of the cavern and the fact that it was, on average, only about 10 metres beneath the surface.
“That is very shallow. To create a large hole, you need a body of rock to support itself above that cavern,” he said, explaining that to provide support a type of concrete known as shotcrete up to half a metre thick was applied. “Working in that city environment is hugely challenging.”
About 28,000 tonnes of concrete have been poured to form the cavern floor, leaving more than a third of its construction completed. Excavation of the cavern and most of the connecting tunnels was finished in May.
Two giant boring machines are due to break through into the cavern by the end of the year, which will complete twin tunnels between the Bays precinct at Rozelle and the CBD. It will mark a shift for the mega project from digging tunnels and giant holes to building and fitting out stations, as well as the laying of rail tracks and installation of vital equipment.
At the western end of the cavern beneath Hunter Street, three giant concrete pillars serve as structural supports for the roof, and will be where three tunnels each about eight metres wide will enter, one of which will be for passengers.
At the eastern end, a giant shaft is being dug from street level into the cavern. It will serve as the other entrance to the station. Passengers will make their way down via banks of escalators and lifts to a concourse level, before taking another set of escalators to the platforms.
The forecast volume of passengers is such that Sydney Metro, a government agency, is considering widening a pedestrian link under George Street between Wynyard station and the western end of Hunter Street station.
A direct pedestrian link will be built between the Hunter Street station concourse and the platform level at the existing Martin Place metro station. Importantly, passengers will not need to pass through ticket gates to walk between the two.
Transport Minister John Graham said the station would be at the middle of an underground spiderweb of connections in the CBD. “It will open up direct connectivity to every metro line and every train line without ever having to go above ground to cross a street,” he said. “[It] is an engineering feat of which the numbers tell the story of its scale.”
Sydney Metro expects to award a major contract within the next six months for the station construction and towers up to 60 storeys above. After Multiplex and Brookfield pulled out of the tender several months ago, the agency has been left with a single consortium comprising billionaire Justin Hemmes’ Merivale, property giants Lendlease and Mirvac, and Coombes Property.
Regan emphasised that the remaining bid needed to represent “good value” and, if it failed to stack up, the agency would revert to building the station and leaving open the ability for towers above to be constructed later. “It’s our preference to do it in one go, but it’s not essential,” he said.
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