It seems that even one of the world's largest tunnel boring machines (TBM) needs a rest now and again. Alice, which is 10th biggest TBM​, has just recently returned to work on the Waterview Connection project after a scheduled mid-winter maintenance break.

The Waterview Connection is a twin set of tunnels in Auckland, New Zealand, that is due to be finished in early 2017. The project joins the city's Southwestern and Northwestern motorways, which allow motorists to avoid the often busy Northern and Southern routes.

Alice completed the first tunnel in September 2014, surfacing in the suburb of Waterview. The machine had started her journey some 10 months earlier south in Owairaka. Civil engineers quickly turned the machine around and began construction of the second tunnel in April.

Averaging around 16 metres a day, Alice restarted her work 58 per cent into the second tunnel – around 1,400 metres into the 2,400 metre project.

NZ Transport Agency's Highways Manager, Brett Gliddon​, is pleased with the progress on the second tunnel and is looking forward to the completion of this part of the project.

"The project team is very happy with progress, and we're on track for a breakthrough in mid-spring," he said in a July 31 media statement.

Scheduled maintenance stop

On a project of this size, civil engineering teams are constantly under pressure to have the machinery working at 100 per cent. This is exactly what the five-day break was used for, with the NZ Transport Agency explaining that Alice required hundreds of steel-fibre brushes changed on her front section, or shield.

During the construction of the first tunnel, engineers encountered the same issue. The brushes are vital as they provide a waterproof seal when the concrete tunnel segments are installed.

"It's inevitable that there will be some wear and tear on the TBM given the scale of the project and the size of the tunnels we are constructing," Mr Gliddon explained.

"She's operating consistently. With the experience gained from the first drive, we're very happy with her underground passage."

Quality waterproofing materials required

As Auckland is one of New Zealand's wettest main centres, particularly during winter, waterproofing is a constant topic during this project. This will no doubt be a concern as civil engineering teams also built a new services culvert within the tunnel, and also a number of cross passages between the tunnels, which will be filled with electrical equipment for the overall network.

Being such a critical project, the Contractor sought advice back in 2010 during the Tender phase from Bluey Technologies, a leader in tunnel waterproofing for Australia and New Zealand.  Not only had Bluey already completed dozens of similar projects in Australia, but it had also successfully sealed the tunnels on Auckland's Northern Gateway project a few years prior.  This local knowledge and overall experience was invaluable on this challenging project.

At Bluey, we are now busy working to seal the cross passage connections between the two tunnels, working closely behind one of the world's largest TBMs. We look forward to delivering another successful outcome for our trusting client.

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