KEY POINTS:
Excitement is in the air at Mairangi Bay as a band of workers from around the world unwrap the latest in tunnellers' toys - a boring machine the size of a freight truck and a train set which looks like a big sausage dog.
From next week, the machinery will be lowered 15 storeys down a chamber into the earth to help build a 5.4km sea outfall for the Rosedale Waste Water Treatment Plant.
Star of the show is the $10 million machine dubbed Amelia Rose, which was built in Canada specifically to handle the rock under Mairangi Bay and coast.
Once down and running, its sharp rotating head will chew through 30m of rock a day from the treatment plant to a point offshore, where it will rise to join a pipeline buried in the bed of the Rangitoto Channel.
Following close behind will be a low-slung train to carry the spoil away and haul in concrete hoops for the tunnel lining, which have jigsaw-like joints to give a tight waterproof seal.
That's reassuring for the machine's operator squeezed into a clearing among the earth-moving auger and a massive web of black hydraulic pipes and cables.
Supporting the machine and its progress for 24 hours a day underground will be 10 to 12 workers a shift, said John Cooper, of Maunsell, which is managing the $116 million outfall project for North Shore City Council.
Contractor McConnell Dowell had assembled a dedicated team of tunnelling specialists from Britain, South Africa and Australia, as well as New Zealand.
They could make progress of 30m to 40m a day compared with the 2m to 3m managed by those who dug out earlier North Shore sewer tunnels by hand.
"Underground, we have the East Coast Bays formation of firm rock - it's good tunnelling," said Mr Cooper.
"It should be finished in nine months to a year, although it's taken five years' preparation to get to this stage."
Tunnelling will follow a curving route which will pass at least 25m under roads, parks and a few homes and businesses.
Mairangi Bay residents won't feel shaking or hear machinery. Mr Cooper said the new outfall would discharge 2.8km offshore, compared with the present one which discharges 600m offshore.
"It will protect the quality of beaches and bathing water and provide the capacity to future-proof the system against the city's growth for many years to come."
Project information and the tunnel-boring machine and railway equipment can be viewed on Sunday from 10am to 2pm at 6A Atlas Place, Mairangi Bay.
It will be the last time the machine will be seen.
"It's too deep to recover it," said Mr Cooper.
"Its valuable parts will be stripped out and it will stay in the tunnel like a metal can."
A barge is working close to the shore at Mairangi Bay as part of testing the sea bed part of the route.
A much bigger Seatow ocean-going barge will be used as a working platform for sinking the pipeline 2m under the seabed.
