Chinese and German manufacturers have been short-listed to build what will be New Zealand's longest new tunnel boring machine for Auckland's $4.4 billion City Rail Link.
Sean Sweeney, CRL chief executive, said the Link Alliance would this month pick who would supply the machine with its fierce 7.15m diameter cutting head. Offers have been submitted from Germany's Herrenknecht, which built the Waterview project's Alice, and China's CREG.
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That machine could cost around $10 million to $12m to build and bring here, compared with Waterview's Alice, worth around $55m, although Sweeney could not go into that level of detail.
Although at 7.1m diameter, the train machine head will be only about half the size of Alice which had a cutting head of just over 14m. Sweeney said the tunnel machine would be 125m long compared with Alice, which was almost 100m long.
The rail tunnel machine will be 1.3 times the length of a rugby field, Sweeney said and the Link Alliance could well name the preferred to the nominated supplier by the end of this month.
And for the first time, details have emerged of exactly how the Link Alliance will transfer its giant machine from its first tunnel to the second: instead of turning underground or being brought to the surface at Aotea, Sweeney said the alliance had decided on an entirely new course.
After digging the first tunnel from Mt Eden, the machine will be brought above-ground at Aotea, broken down into transportable components, trucked back to Mt Eden in parts, reassembled, re-launched and dig the second tunnel in the same way direction.
"Both tunnels will be drilled from the Mt Eden end," Sweeney said, the area used for both starting stages because it has the biggest lay-down or working yard, Sweeney said.
"Karangahape Rd is just too small. We wouldn't have the room," he said, also dismissing the Aotea site on Albert St in the busy centre of Auckland "so Mt Eden is the best place".
Where the thousands of cubic metres of earth from the tunnels will go is yet to be announced and Sweeney said that was an important aspect for the alliance, being so expensive to move the spoil out of the city. Spoil will be ejected by the machine as she moves, via a convey-belt system. The machine will be electricity-driven, just like Alice, due to the danger of petrol or diesel fumes underground, Sweeney said.
Demolition of existing buildings around the 2ha Mt Eden station site will begin soon, then retaining walls will be built around the giant pit to be opened up for works to start. A tower crane will be required, then excavation of the tunnel portal will begin.
Around 20 people will work on the machine at any one time, including logistics staff at ground level. The tunnel boring machine will be shipped to New Zealand, assembled on the site and then dragged down to begin its journey behind a bulldozer or other heavy earth-moving equipment, Sweeney said.
"It will be like a factory, it's a big site." Two tunnel boring machines were considered but regarded as unnecessary as no time or cost savings would result. Then it will drill across the city to K Rd. At the same time, workers will be digging from K Rd 42m underground to create "caverns" which will form that station along the route.
Two shafts would be drilled so the station could create "and those will have to be completed by the time the TBM arrives", Sweeney said, with far bigger cavities dug for each station than the machine could create: "The machine doesn't have the width to build the stations."
In tunnellers' tradition, the machine will get a female name, expected to be in te reō Māori, with competition around that milestone.
Like Alice, the machine will line the tunnels as she goes, inserting 7m+ rings of steel-reinforced lined concrete rings. As she creeps through the earth, those circular concrete rounds will be fed into her mechanism so that as she moves, she completes a section of the tunnel - except for laying the railway tracks which comes later.
Sweeney said 2000 rings would form the tunnels, each circle made of six slightly curved segments to give a round, "cutting and lining as it goes".
"They change in geometry as the tunnels form curves, to go around corners. It's not just tunnelling running in straight lines. Few tunnels do that."
The Aotea station will be around 400m or nearly half a kilometre long, running the full length of Albert St between Wellesley St and Victoria St. And while at K Rd, shafts will be drilled down from the top, creation of the Aotea Station would be simply ground excavation works expected to be 400m long x up to 50m wide.
The segment Mt Eden-Aotea will be 3220m.
CITY RAIL LINK:
• $4.4b project to deliver two 3.4km-long tunnels
• Not due to be finished until 2024
• Tunnels from Britomart to Mt Eden
• Cut and cover tunnels dug at Britomart end
• Tunnel contract awarded to French-dominant Link Alliance
• New stations: Aotea on Albert St, Karangahape Rd
• Jointly funded by Government/Auckland Council
• Aucklanders make 100m public transport trips a year
• CRL opens the rail network for major expansion