Auckland Council staff are inspecting the foundations of the $200 million, 56-level Seascape apartment block on Customs St East, with a council officer expecting final sign-off on that below-ground stage around the middle of this year.
Jeff Fahrensohn, the council's field surveying manager, said examinations were being carried out on areas of the diaphragm wall in the CBD's deepest hole, to ensure compliance.
"The council has moved into the final phase of investigations happening on the site. Six areas are being exposed around the outside of the basement. The first was uncovered about six months ago and we are going through six panels," he said.
"We would expect signoff on the foundations around mid-year."
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Those six areas run down to about 5m below the ground, and were 6m to 10m wide, Fahrensohn said.
And although some reports have referred to defects in the diaphragm wall between Gore St and Commerce St, Fahrensohn said: "I hesitate to use that work defects. This is normal procedure, always expected and the same process was carried out during many other jobs with diaphragm walls including construction of the Victoria Park tunnels and for the Kirkbride Rd underpass at Mangere."
New Lynn's rail trench was another example of a site with a diaphragm wall.
"What is happening at Seascape is an internationally-accepted way to build underground without having to tunnel."
The tower will be New Zealand's tallest at 187m above ground level, or 203m from the lowest foundation floor to the tower's apex. That is higher than the 178m, 52-level $300m Pacifica tower, now being built a block away. However, the two projects are at very different phases - Pacifica is nearing its top level while works at Seascape are still below ground.
China Construction is building Seascape, while Icon Construction is building the Pacifica.
Nick Gillespie, structural practice leader at engineers Mott MacDonald, who is working on Seascape, said work was going completely according to programme, there were no delays of any significance and nothing unexpected.
Engineering business Beca had prepared an independent review of the work and presented that to the council, he said.
That Beca report had concluded that further evidence was required to demonstrate compliance of the project's diaphragm wall construction.
"The project team agrees, and to that end is currently exposing portions of the far face to investigate the built condition. The first of these has recently been completed and has provided the positive results that were expected. These investigations are continuing in parallel with construction works within the basement, and are not affecting progress on site," said Gillespie. The project is expected to be finished around 2022.
Construction was continuing in accordance with the project programme, he emphasised.
There had always been a plan for investigations of the external face of the diaphragm wall, which the project team raised as a result of the risk of defects that being encountered.
In December, Gillespie told the Herald: "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."