What are the two key risks to New Zealand's biggest infrastructure project, the $4.4 billion City Rail Link? When will the first tunnels be bored underground from Mt Eden? What stage is the preferred bidder at? In the first of a two-part series Anne Gibson looks at the next most crucial phase of the project.

A giant tunnel-boring machine able to hollow out two separate 7m diameter passages will be shipped to New Zealand soon for work on the CRL passages in Auckland.

With the catchcry of "getting Auckland's heart pumping", the Link Alliance for the crucial C3 or tunnel/station phase of this country's largest transport project probably won't start tunnelling until next year.

That's according to Dr Sean Sweeney, chief executive of CRL - the Auckland Council/Government joint venture - the academic and lecturer, mega-project specialist and New Zealander, with an international pedigree for conquering some of Australasia's largest, hardest jobs.

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Sweeney is a man who chooses his words carefully and has a defined, considered dress sense. On a casual Friday he wears a T-shirt and unbuttoned shirt, with chinos and Harry Potter-style glasses. He is elegant, understated, sitting at CRL's boardroom table overlooking Albert St, explaining project detail, showing such complicated and detailed flow charts and organisations structures that the print is hard to discern.

"I can't let you take these away with you, but I wanted to show you," explains Sweeney, pulling out from his folder first the Link Alliance project team chart with names of every person in a position of major responsibility and their titles, then a separate timeline chart of what's done when, by whom.

Sean Sweeney, CEO of the City Rail Link. Photo/Greg Bowker
Sean Sweeney, CEO of the City Rail Link. Photo/Greg Bowker

It's his Kiwi and practical way of displaying project complexity. The big Link Alliance team has for months been based in a building around the College Hill/Victoria St West precinct.

Aspects of timing, logistics, workflows and planning are now up to that preferred bidder. And it's precisely that level of detail which is now being worked on, creating organisational structures and forming tenders to be issued for construction, materials, electrical, plumbing, concrete, steel, electronic, transport, hydraulics, mechanics, station building, etc.

Even where the tunnel-boring machine will be built - perhaps China - where it will start, how it will get into its very hole underground - perhaps by widening the existing Mt Eden station - what it will be called, how it will emerge and precisely where - none of these things can Sweeney say for sure because they are not necessarily aspects under his control.

Much of this fascinating project is the opposite of its location - up in the air, not subterranean.

"I think it will start at Mt Eden and pop up at the Aotea Station," says Sweeney, sitting in the L17 boardroom of CRL's offices in the AMP Centre, Lower Albert St corner. "But it's up to them."

He is, however, very sure of, something somewhat frightening: the project's two biggest enemies. In this candid interview, he disclosed the two unknowns which he sees as potential threats.

City Rail Link's trenches being built. Photo/Jason Oxenham
City Rail Link's trenches being built. Photo/Jason Oxenham

1. Operational threat: connection to the existing system

"The biggest concern is with the connection of what we build to the live network and the certification from a safety, fire and operational point of view. We don't control everything because we are connecting into an existing network. That will be the hardest challenges," Sweeney disclosed.

He then cites issues at Europe's largest infrastructure job, Britain's 118km, £17.6 billion Crossrail, expected to be finished by early 2021, running from Reading to Heathrow, passing through 42km of tunnels beneath London, striking problems with the integration of three separate signalling systems on the Elizabeth Line, subsequent testing slower than expected.

Sweeney is watching that daunting project with close interest.

How the new Aotea station might look. Photo/City Rail Link
How the new Aotea station might look. Photo/City Rail Link

"Crossrail went very well until now, towards the end. They have had problems getting their systems to work. The [new] trains' operational system has to go through three different operating systems - above ground, heritage underground and underground."

The closest analogy he can give to the somewhat terrifying challenge of that aspect of the Auckland job is that "it's like trying to get your [Microsoft-operating system] PC to talk to your Apple [computer]" - and then possibly link up with the washing machine.

"Technically, people will say it all works but when you want to do something tricky, you find out it doesn't. Trains will be put through an exhaustive range of scenarios, say, for a nearest-station emergency. I'm told this train system [in Auckland] is quite modern, so unlike what London is dealing with."

2. Secret lava flow rock/bluestone basalt, Mt Eden

Potential lurking lava rock flows could be the TBM's biggest enemies and the project's second-biggest threat, Sweeney says. The tunnel-boring machine would be pushed to cut such hard rock. It is more likely built to cope with the softer Waitemata sandstone which dominates underground in these parts of Auckland. If the rock is found, the expertise of explosive specialists might be needed. It might be blasted, not cut.

Sweeney says extensive ground test bores have been drilled to ascertain conditions for the TBM: 3000 test bores by CRL experts alone but further test results from another 3000 boreholes by external parties.

No one really knows the ground conditions 100 per cent until the tunnels are dug. And by then, if those secret rock flows do emerge, that could spell big trouble.

The project is to be completed by 2024. This next stage of C3 is by far the most expensive and the most complicated.

Instead of the far more straightforward and less expensive cut-and-cover trenching technique used from Britomart to beneath the $1b Commercial Bay then up Albert St, C3 involves working at a depth of up to 42m to dig the tunnels.

The double-track rail tunnels will run underneath Auckland's city centre from the Britomart Transport Centre all the way to Mount Eden Railway Station, built by two construction techniques: cut and cover and tunnelling.

On the $1b cost increase, Sweeney cites Megaprojects and Risk: An Anatomy of Ambition, the book by Bent Flyvbjerg which he said shows that large project end-costs rise by around 43 per cent to 45 per cent from initial stages to completion.

"Project teams have an unconscious desire to keep the numbers low. The cost of CRL now reflects current market conditions."

Interestingly, CRL has paid to use the intellectual property of the second bidder which did not win the job. Sweeney says: "We took the view both of the bidders have very smart people and they came at the job two different ways. We said we'd pay the second bidder."

The project alliance agreement might be signed around July but variations could push that date out till around September.

The Link Alliance is Vinci Construction Grands Projets, Downer NZ, Soletanche Bachy International NZ, WSP Opus (NZ), AECOM New Zealand and Tonkin + Taylor Limited.

Bosses from around the world will be running the tunnelling contract but two French names could become more well-known: Francios Dudouit from global business Vinci is the Link Alliance project director and a world tunnel and rail expert, a leader in his field. Engineer Pierre Bourgeois, also from Vinci, is another chief. Alan Howard-Smith of Downer Infrastructure is communications and stakeholder manager.

Sweeney says CRL's C3 staff will come from France, Hong Kong, the Philippines, Malaysia, Burma, Doha, Tibet, Sri Lanka - "wherever there are major underground tunnel works going on".

For him, this phase is the best: "This is really exciting. Now, we have the major bidder and we have been through our refunding costs. It's incredibly exciting. For the first time, we have a clear line of sight. A lot of the project uncertainty has been reduced. Just don't quote me as saying I can see the light at the end of the tunnel."

City Rail Link in numbers

• $3.4b cost estimate forecast in 2014 before project started;

• $4.4b expected completed project cost announced in April;

• $1b increase from sector price rises, project scope extended;

• Twin-tunnels 3.4km long with two new stations - Aotea, Karangahape;

• Tunnels 7m diameter, compared to Waterview's 14m diameter;

• Tunnels will be up to 42m below ground surface;

• Ground-breaking: June, 2016 with ex-PM John Key.

NEXT: What will the $4.4b City Rail Link tunnelling machine be called, where and how will she work?