Mega-mole Alice nears daylight

Waterview's tunnel boring machine in action. Photo / Jason Oxenham.

Auckland's mega motorway tunnelling machine is powering its way below Waterview with only about 300 metres to go before reaching daylight early next month.

But that will be merely the half-way mark for the 2800-tonne tunnel boring machine.

It will then have to be turned around over several months to dig the second of a pair of 2.4-kilometre tunnels needed to link the Southwestern and Northwestern motorways, and complete the region's 47-kilometre western ring route alternative to State Highway One.

Yesterday, the tunnel boring machine - called Alice after a schools' naming competition - was inching towards its goal about 18 metres below the surface, just east of the intersection of Great North Rd and Oakley Ave.

Despite the roar of 24 engines powered by 22,000 volts of electricity to turn the machine's giant 14.46m cutting head with its almost 300 tungsten cutting tools at a rate of just under two rotations a minute, an almost total lack of vibration meant it would have been impossible for anyone on the surface to guess its exact position.

That is just as well, as the $55 million machine has tunnelled directly below the Mt Albert Pak 'n' Save supermarket and Oakley Creek on its journey from Alan Wood Reserve in Owairaka, from where it set off in November.

Although the machine thrusts itself forward by 20m to 24m a day, lining the project's future southbound tunnel with 100-tonne rings of prefabricated concrete as it goes, construction manager Iain Simmons says it will have to ease the 5000 tonnes or so of pressure it exerts on ground ahead as it prepares to emerge through a portal near Waterview Primary School.

The Transport Agency, which has contracted Mr Simmons' Well-Connected Alliance of companies to build the $1.4 billion Waterview link, has yet to put a date on when in early October it expects the machine to break into daylight given complex engineering needed for that operation.

For Mr Simmons, that will simply signal the start of four months of manoeuvring the tunnelling boring machine around in a tight trench excavated next to an embankment which will carry traffic on to a motorway interchange with support structures already towering 20m above the ground.

Once the machine is fully underway on its return journey, after a two-phase turnaround operation for its 88m train of pipelaying and conveyor belt installation equipment, the contractors will begin drilling 16 cross passages between the main tunnels to provide escape routes in emergencies.

It is being trailed all the way by a set of extendable conveyor belts which have so far removed about 330,000 of spoil from the tunnel to a drying plant next to Richardson Rd in Owairaka, from where it is being trucked 17km back along the Southwestern Motorway to become fill for an industrial development site over a disused Wiri quarry.

Although the second tunnel is expected to take only until about next September to dig, there will be plenty more work to be done including building venting towers at both ends before the full 4.8km Waterview Connection - half of which is being built as a surface motorway - opens to three lanes of traffic in each direction.

About $600 million is also being spent on associated projects, mainly widening the Northwestern Motorway in both directions between Te Atatu and Point Chevalier to cope with extra traffic from the Waterview link, which will become a major route between central Auckland the airport.

Transport Agency highway manager Brett Gliddon said the various projects were making good progress for completion in the first quarter of 2017, although it was still too early to firm up that target.