Construction of New Zealand's tallest apartment tower is still on track for 2022 completion despite foundations taking longer than initially expected.
Nick Gillespie, engineering project director of Mott MacDonald, said foundation work at the $200 million 56-level Seascape on the Gore St/Customs St East corner had been more complicated than initially expected because neighbours, including the Oaks apartments on Gore St, objected to allow work underground.
"Construction has been under way for some time but it's going to programme. It's an interesting form of construction with an internal set of props," Gillespie said from the site, showing off the giant Chinese-imported steel props with minor surface rust but strong enough to support the gigantic basement retaining walls.
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Those props will be craned out and moved to other sites as each basement floor is built, he said.
"This form of construction for a basement does take some time but it is running to programme and running exactly as expected," Gillespie said.
Jeff Fahrensohn, the council's field surveying manager, said he was waiting on independent consultants to do a peer review. That will examine any defects in the walls which are voids or areas where concrete has been mixed with mud or slurry but he also stressed he was unconcerned and such defects are common. Council inspection teams meet monthly with China Construction, he said.
"We're comfortable with their strategic direction. There are no red flags," Fahrensohn said.
Gillespie said foundation work was taking longer than originally expected.
"There were some inefficiencies in the design which influences the duration of construction," he acknowledged, referring to the neighbouring Auckland Harbour Suites/Oaks refusing consent for ground anchors beneath it.
The tower will be New Zealand's tallest at 187m above ground level and 203m from the lowest foundation floor to the tower's apex, he said. That is higher than the under-construction 178m 52-level $300m Pacifica, a block away.
But he said despite one media report on December 3, it was not true that foundation concrete was flawed or that there were any problems with construction nor that Auckland Council was awaiting a report.
"The allegations about hold-ups due to defects in the diaphragm wall are incorrect. There will always be defects on perimeter diaphragm wall construction whether in New Zealand or overseas. This is not out of the ordinary. It was entirely expected. The defects don't concern us. We're using tried and tested concrete repair techniques to address the localised defects in some panels of the walls. Only one set of inspections remain to be completed."
He refuted an RNZ article published on December 3, also published by the Herald.
The Herald was invited on a tour of the site with:
• Sathy Thurai-rajah, construction manager, China Construction NZ;
• Les Honeyfield, the senior project manager from China Construction NZ;
• Bradley Luke, principal architect, Peddlethorp;
• Nick Gillespie, project director of engineering, Mott MacDonald;
• Simon Ma, senior project manager, Shundi Customs.
The five men gathered to explain the unusual method of foundation construction which one said was a little like creating a gigantic bathtub but with the water on the outside - and no plughole.
The basement will be 21m deep, "making it the deepest sub-structure in downtown Auckland", Gillespie said.
Thurai-rajah said Seascape's cavernous basement would be deeper than SkyCity's underground car parking because those areas further up town were on the sloping ground whereas Seascape's was just one massive verticle dig.
"This is the deepest basement or foundations ever dug in downtown Auckland," said Thurai-rajah of the five-level excavations, "deeper than the City Rail Link tunnels beneath Commercial Bay. The basement alone is a $70m job."
Five underground car parking levels are being created there for 152 vehicles, with an additional 40 car parks above ground in the tower on levels five and six.
There will be 192 car parks altogether, he said.
The scope of works alone made the job unusual, he said.
Time taken to build the foundations was due to the neighbours' non-approval "which is their right", job complexity, foundation depth, the fact that all excavated material has to be lifted out internally from the site, tight and busy street constraints and pouring concrete limitations, Thurai-rajah said.
"We can only pour large amounts of concrete on the weekends," he said, citing Auckland Transport issues, partly due to Quay St lanes reduced as extensive work was carried out there.
Gillespie said the basement levels could have been built far faster if internal ground anchors were able to be used to restrain the diaphragm walls "but those negotiations couldn't be completed with the neighbouring properties, so we had to go down this route."
If allowed, those anchors would have run around 18m to 19m deep beneath the Oaks, he said.
Anchors do, however, run under the existing White Rabbit building and under the existing Ballantyne office building, Gillespie said. Those two buildings flank Seascape's basement and are part of the project. The White Rabbit has Seascape's scale model, sales suite and Shundi offices and the Ballantyne building will be refurbished to become the hotel.
Ma said around 20 per cent of apartments were pre-sold with 10 per cent deposits paid and Seascape's developers intended to apply for Overseas Investment Office consent for a standing consent so foreigners could purchase the residential units.
Thurai-rajah said the basement would be finished by February, the project would reach ground level by November next year and the building would be "topped out" by the third quarter of 2022.