Sixty per cent of work on the Bay Link project has been completed, NZTA says, as construction on the Bayfair flyover begins.
Four supersized steel cages have been craned into the middle of the roundabout, providing the structure for the columns of the flyover's first pier.
Waka Kotahi NZ Transport Agency infrastructure delivery regional manager Jo Wilton said to be moving into the next phase of construction was fantastic.
"Most of the progress at the northern end of the project has been below ground to date. Now the ground improvements are complete, focus at this end shifts to construction of both the underpass and the flyover."
The four eight-metre-long steel cages provide the steel structure for the four columns that will form part of the bridge pier.
The Bayfair flyover will be supported by three piers in the middle and two abutments at either end, which is a change from the original design.
To accommodate a new underpass, the Bayfair flyover required an additional bridge span, taking it from a three-span to a four-span bridge.
At the Bayfair end of the project, the flyover will take Stake Highway 2 traffic over the roundabout, which is being upgraded to a larger version with traffic signals.
The Bayfair flyover is one of three bridges to be constructed as part of the Bay Link project. Two bridges are under construction at the Te Maunga end, which is anticipated to open to motorists at the end of 2021.
"The Bay Link project aims to improve safety by grade separating the railway level crossing, as well as splitting up state highway and local road traffic," Wilton said.
"Separating heavy freight vehicles from local traffic will also help improve overall traffic flow."
As part of the construction process of the Bayfair flyover pier, the steel cages sit on a concrete and steel footing located on top of the recently completed lattice pile ground improvements.
Each vertical cage will be encased in concrete before a pier head is poured on top.
To align with construction sequencing, the next two Bayfair flyover piers are planned to get underway early next year.
"In addition to the flyover getting underway at the northern end of the project, construction is also taking place on the eastern and western portals of the new underpass, which will be pleasing news for the local community who strived to retain a crossing under the state highway."
More information about the underpass is expected in the coming weeks, Wilton said.
Despite being 1.7km in length, construction of the project is taking place within a highly constrained environment, with challenging soil conditions on a narrow, urban, arterial corridor catering to approximately 38,000 vehicles each day, she said.
"The project is approximately 60 per cent complete and is anticipated to be finished in late 2023. We know everyone who lives and works alongside, and travels through, the project is looking forward to its completion as much as we are."
• The four steel cages that will form the four columns of one of the flyover piers are eight metres long and weigh approximately three tonnes each
• Each cage sits approximately three metres below ground on a footing, which is located on top of the recently completed lattice pile ground improvements
• Around 30 tonnes of reinforcing steel has been used in the footing. Each vertical cage will then be encased in concrete before a pier head containing a further 10 tonnes of reinforcing steel is poured on top
• This pier, containing approximately 50 tonnes of steel in total, will support the beams for the Bayfair flyover once all other bridge supports are complete.