Big Concrete Pour a Milestone for Melbourne Tower Foundations
More than 150 bored and continuous auger flight piles, drilled some 45 m into the Melbourne Formation, will use some of the strongest concrete ever in the city's central business district.
Photo courtesy Geotechnical Engineering
Piling works on Melbourne, Australia's 319-meter-high Australia 108 tower, which is set to become the tallest residential building in the southern hemisphere, passed a milestone mid-February with a 175-cu-m concrete pour, the project’s biggest to date.
Geotechnical Engineering says piling on the $900-million, 100-level, 1,105-apartment block is expected to be completed by mid-March. Work involves the installation of more than 150 bored and continuous auger flight (CFA) piles up to 2.1 m in diameter and drilled some 45 m into the Melbourne Formation.
It also includes some of the strongest concrete to be tremied in the Melbourne Central Business District, says Nic Morgan, general manager, Geotech Pty Ltd., of Port Melbourne, Australia. “In general it’s mainly 80-MPa (megapascal) concrete—although [the stronger mix] is, we believe, the first 100-MPa concrete to be tremied in the Melbourne CBD.”
Bored piles being driven under polymer fluid include 12 at 1200-mm-dia, 10 each at 1500-mm- and 2100-mm-dia, and 16 at 1800-mm-dia. “They’re founding generally at a depth of 40-45 m in the Melbourne Formation,” says Morgan. The heaviest reinforcing cage to date is 50 N40 bars, some 25 tonnes, he adds.
CFA piles include 55 at 600-mm- and 50 at 900-mm-dia, generally founding at a depth of around 37 m. “There is also a section of secant-piled wall inside the heritage facade along City Road, while jet grouting, which has not yet started, will be required at the base of the core structure.”
Geotech is using an Enteco E25 M, with a capacity of 53 tonnes per m, for CFA operations. The machine is currently the largest CFA rig in Australia, says Morgan.
“The basalt flows encountered across the northern side of the site have proved to be significantly more substantial than expected, causing considerable pressure on the program,” Morgan says. “But our client is understanding, and we are getting there,” he adds.
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Some residents could move into the tower below the 41st floor as soon as 2018, when the building is less than half finished, as the project will be completed in five stages. Another 15 stories or so will be opened every six months until the building is completed.
Also known as 70, Southbank Boulevard, in Melbourne’s Southbank business district, Australia 108 is being built by main contractor Brookfield Multiplex. The tower will feature three levels of world-class residential amenity, including two infinity pools located 210 m above grade. Designer is Fender Katsalidis Architects, for developer World Class Land. Structural Engineer is Robert Bird Group, and geotechnical consultant for the project is Golder Associates.
Brookfield Multiplex regional managing director Graham Cottam said the company’s appointment followed a successful Early Contractor Involvement process with World Class Land. “We were able to build a partnership during the planning phase of the project and achieve the project deliverables,” he says.
