The demolitions and re-housing of residents have allowed Waterview Reserve to be moved west to make way for a slew of cranes. They are this month starting to construct a giant motorway trench by ramming concrete slurry into the ground to form the walls before earth is scooped out between them, behind 3.5m noise barriers on the project's border along Great North Rd with Waterview Primary School.
Drivers whose motorway trips from Manukau now end abruptly at Maioro St will get faster passages to West Auckland or the city centre, via connections to the Northwestern Motorway at Waterview.
"The penny drops when they see the extension of the alignment and realise Maioro St [where traffic is already using the first half of a motorway interchange] makes sense," says Transport Agency northern highways manager Tommy Parker.
Although the motorway extension will displace much of the green belt between New Windsor and Owairaka, the agency hopes to reduce community severance with a footbridge over its six lanes of traffic, to provide a walking and cycling link between Methuen Rd and Hendon Ave. The Southwestern Motorway will run through the tunnels at depths varying from 10m to 45m before resurfacing next to the Waterview school. That is being demolished over the summer break and replaced with temporary classrooms before being rebuilt with acoustic insulation against the future roar of emerging traffic.
From there, the motorway will rise over the mouth of Oakley Creek - a refuge in pre-European times for local Maori against raiding parties - across which a wetlands boardwalk will be built to Eric Armishaw Park in Pt Chevalier.
Work is also expected to start under a separate contract within two or three months on raising and widening the Northwestern Motorway's marine causeway to Te Atatu, which will push the bill for the overall project - including roadworks back to St Lukes - to $2 billion plus inflation.
The main work so far under the $1.4 billion primary contract has been in Alan Wood Reserve, where a $54 million boring machine will arrive in parts from China in June or July to be assembled before spending a year from October digging the first tunnel.
It will then be turned around for a repeat performance in the opposite direction to complete the final link in Auckland's 48km western ring route by 2017, or sooner if the work can be sped up to align with completion of the causeway upgrade.
Mr Parker says one of the biggest challenges of the project will be building 15 service passages between the two main tunnels, using more conventional technology.
As well as clearing the alignment for the surface motorway from Mt Roskill, the contractors have already dug much of an approach trench, about 300m long and 45m wide, into the southern end of the future tunnels.
They are using explosives to blast their way through a thick layer of extremely hard basalt to softer sandstone. That will create a hole at the end of the trench which will end up about 100m long and 35m deep, in which the tunnel boring machine with its 13.3m-diameter drilling head will be assembled.
The hole was resembling an open-pit mine when the Herald toured the site just before Christmas, and the contractors were through much of the basalt, but at a depth of 15m they were still only at the top of where the tunnels will be bored.
They were strengthening the sides of the trench for it to be straddled by a 600-tonne gantry crane needed to lower into place what Mr Parker says will be the biggest piece of construction machinery in New Zealand's history.
Another project biggie is a pre-cast concrete factory being built at East Tamaki to churn out 24,000 10 tonne segments which will be loaded into the boring machine to line the tunnel walls automatically as it pushes and pulls itself under electric power through about 10m a day, using an "earth pressure balance" system to stabilise the ground as it goes.
The technology will allow the construction alliance to bore all the way beneath Great North Rd in Waterview without having to disrupt traffic with a "cut and cover" trench towards the northern end of the tunnels, as planned initially.
That removes the need for a large construction yard beside a sensitive lower reach of Oakley Creek, a proposal which came under heavy fire at a marathon planning hearing in 2011. However a trench will still have to be dug across Great North Rd towards the end of the project to connect a 15m venting tower for vehicle fumes to the tunnels.
The project also requires about 1.3 million cubic metres of spoil to be removed to a former quarry site in Wiri, 800,000cu m of it from the tunnels, which will reach the Southwestern Motorway on a temporary haul road to reduce disruption to local streets.
General traffic will be kept flowing at the normal speed limit along busy Great North Rd during much of the project, although there will be some reductions when the tunnel machines passes directly below.
Job much bigger than locals imagined
Community leader Margi Watson says the sheer scale of the Waterview project is something which even residents who have been steeling themselves for many years are struggling to grasp.
"The reality of the size of the construction zone is bigger than you could have imagined - it was unimaginable exactly what it would look like but now we can actually hear the noise, feel the vibration and the vehicles, see the flashing lights."
Ms Watson says the lack of passive green space in the southern sector, and almost daily rock blasting during which nearby residents have to leave their homes with sweeteners of supermarket or fuel vouchers, has proved more disruptive than most expected.
So has the loss of so many buildings at Waterview, where the community has welcomed the early provision of alternative recreational facilities while remaining frustrated about obstacles to entering and leaving the suburb, whether on foot or by car.
But she pays tribute to efforts by the Well-Connected Alliance of the Transport Agency's contractors in working with the community to try to soften impacts of the project where possible.
"I think every opportunity they have had to make it better, the alliance has done that," she says.
Alliance spokesman Gez Jones says the blasting at the southern end of the project was considered preferable to breaking up the basalt with jack-hammers, which would have been far noisier, although that is being done on a relatively small scale for a new sewer line being laid too close to houses for explosives to be used.
He says the blasting is likely to continue until March but there is no basalt requiring explosives at the northern end, and the alliance is looking forward to restoring landscapes at both locations to the best of its abilities.
