It was Groundhog Day in Auckland this morning as Alice the giant boring machine punched out of the ground to complete the second of two long motorway tunnels.

The breakthrough, into a deep trench in Owairaka's Alan Wood Reserve at 11.50am, was greeted with cheers from Transport Minister Simon Bridges among guests perched on a temporary grandstand and hundreds of workers watching video feed from a nearby marquee.

That followed more than two hours of high- and low-pitched grinding as the machine's 14.45m cutting wheel chewed through a concrete wall after kicking back into life at 10am from an overnight rest in which extra sharp tungsten blades were fitted.

One man among dozens of Transport Agency guests from industry and the local community likened it to the deep ocean call of a whale.

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Mr Bridges told reporters after the breakthrough that he liked to think it took a lot to impress him "but that was seriously impressive to see those massive pieces of concrete coming through like something out of Mad Max".

But he quickly added that the smash-up had been worked out technically years in advance with intricate detail.

Alice the giant boring machine. Photo / Jason Oxenham, NZ Herald
Alice the giant boring machine. Photo / Jason Oxenham, NZ Herald

Mr Bridges admitted on arriving in the trench overlooking a massive iron circle delineating where the machine was due to burst forth that he was even more excited than he had expected.

"This is pretty cool - this is some pretty serious engineering," he remarked to the Herald.

Today's was the machine's second breakthrough. It has put Alice back next to where it began a 4.8km subterranean journey to Waterview and back just under two years ago
Although the Transport Agency's Well-Connected Alliance of contractors still has another 18 months of work ahead to complete the $1.4 billion Waterview Connection project, the $55 million machine will be dismantled almost immediately and returned to its German manufacturer under a buyback deal.

Guests wait in a specially erected grandstand for the breakthrough of Alice. Photo / Jason Oxenham
Guests wait in a specially erected grandstand for the breakthrough of Alice. Photo / Jason Oxenham

Although the 2800-tonne groundhog has had a top speed of 8cm a minute - about the pace of a ravenous snail - today's operation was particularly delicate as it eased its way through the final concrete barrier under precise laser guidance. The challenge was for its operator to keep its potential pushing force of 300,000 tonnes under tight restraint.

And then, after being put into neutral for several minutes, the monster began its final grind to send huge chunks of concrete tumbling to the bottom of the tunnels' approach trench in a cloud of dust and a massive crash.

The pile of rocks was covered in foam which gushed from the tunnelling machine, making it look like a snowy outcrop.

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In a statement, Mr Bridges said the ring route - one of the Government's seven roads of national significance - was crucial to dealing to congestion in the country's largest city.

"This breakthrough means we are well on our way to completing the Western Ring Route, which will create a 48km alternative route around Auckland and reduce dependence on State Highway 1," he said.

"Waterview is more than just a huge infrastructure project. It has earned international acclaim for the skill and innovation contractors have brought to its design and construction."

The Transport Agency's Auckland highways manager Brett Gliddon said it was the country's largest ever roading project.

"Today's breakthrough is a massive milestone for a project that will transform the way Aucklanders get around their city - a brilliant and remarkable effort and a proud day that needs to be celebrated," he said.

Alice, the tunnel boring machine working on the Waterview Connection in Auckland. Photo / Jason Oxenham
Alice, the tunnel boring machine working on the Waterview Connection in Auckland. Photo / Jason Oxenham

"The risks associated with constructing tunnels twice as long as the Auckland Harbour Bridge were always high and the Waterview team rightly needs to be congratulated for its engineering skills and innovation to complete this job safely and on time. That's a fantastic achievement."

During its time underground, Alice excavated enough dirt to fill 320 Olympic-sized swimming pools and installed more than 24,000 concrete segments to line both tunnels.
There is now a busy programme of work to complete both tunnels.

Sixteen cross passages linking the two tunnels are being constructed, equipment to safely operate the tunnels together with lighting and signage are being fitted, walls and the ceiling are being painted, and back-filling continues before the motorway asphalt is laid.

The Government plans to open the tunnels and the adjacent Great North Rd interchange in early 2017.