KEY POINTS:
Most of the new bridge piles have been sunk into the Manukau Harbour on the country's second-largest roading job.
John Burden, the Fletcher Construction alliance project manager in charge of the $230 million Manukau Harbour Crossing project, said the majority of piles were now in place on the
job, which ranks second only to the $365 million Northern Gateway Albany-to-Puhoi project.
"About 70 per cent of the piling is finished and 40 per cent of the seven piers needed for the Mangere Bridge are completed," Burden said from his site office almost directly underneath the bridge.
About 200 people from an alliance of companies are working to build a key link in the Western Ring Route project, designed to join motorways between Manukau and Greenhithe. The key link between Onehunga and Mangere is on target to be finished before the 2011 Rugby World Cup.
The Manukau Harbour Crossing Alliance is made up of NZ Transport Agency, Fletcher, Beca Infrastructure and Higgins Contractors.
They are creating the link for traffic flowing from Manukau to the Mt Roskill Extension project, designed to ease airport traffic delays and a step towards completing the 48km Western Ring Route which lacks the key Waterview extension.
But before the builders added to above-ground infrastructure on the State Highway 20 job, first they went down.
Divers have been working 5m underwater in coffer dams - part of the pile construction - beneath the harbour to ensure seals are true around piles, driven as far as 50m beneath the seabed directly into Waitemata sandstone.
"The sandstone is weak but we get enough of a socket to take the load," Burden said.
Above ground, teams are prebuilding sections of the new bridge to span the harbour and double traffic capacity between Auckland International Airport and the extension of State Highway 20 through Mt Roskill, Waterview and across to the Northwestern Motorway at Pt Chevalier.
Elements of the bridge are being precast within metres behind the alliance's site offices off Coronation Rd and then swung into place by some of the eight cranes on the site.
Pier tables, each weighing 70 tonnes, are being built in those yards, while 9m-high bridge columns are being built in situ in the harbour.
The new bridge rising on the eastern or city side of the existing Manukau Harbour - on the left driving to the airport from the city - has provision for rail but its main purpose is to take four lanes of southbound or airport traffic.
The existing bridge will take a duplicate four lanes of northbound or city traffic, doubling capacity when it opens in 2011. Burden said the twin bridges would have only a 2m gap so, once the new bridge was finished, that section would appear to motorists like any other large section of the motorway because the new bridge would be on the same level as the existing Mangere Bridge.
The alliance will then remove the median barrier on the existing bridge, creating a total of five lanes including the bus priority lanes.
Ten lanes of motorway, including two bus lanes, are being created with the State Highway 20 job.
"We plan to complete the project early in 2011, well ahead of the target and at the moment we're bang on target," said Burden whose previous job was the $300 million Northern Busway on the North Shore.
Ground works are almost finished on the southern section to widen SH20 to three traffic lanes and a bus shoulder lane in each direction. Paving that area is about to start.
Innovation is a feature of the job. Higgins has laid a trial section of cement-treated basecourse alongside the motorway near Walmsley Rd, examining alternative road-building technology which Burden said might allow a more durable and longer-lasting product to be used for the motorway and bridge expansion.
Burden said costs had risen on the job, particularly steel, oil and diesel, in the past few months. Diesel-powered machinery, steel reinforcing used in building bridges and motorways and oil used for bitumen are key components.
FAST TRACK
Manukau Second Harbour Crossing job:
* Expanding Mangere-Onehunga motorway.
* Fletcher began bridge project in April.
* Job to be finished in the next three years.
* 'Future-proofed' for an airport rail link.
* 10-lane highway to airport being created.