Construction work paused on 20 February after the TBM, with support from a temporary gantry setup, had excavated the required 270m of the second tunnel.

New Zealand Transport Agency highway manager Brett Gliddon said: "There is now enough room bring all the necessary gear into the tunnel so that we can complete the job."

The temporary gantry has to be removed. And the two remaining gantries – which contain all services and backup equipment for TBM operation – have to be pulled from the first tunnel, turned 180 degrees inside the Northern Approach Trench (NAT), and then reconnected to the cutter head. The culvert-laying gantry being used to build the services culvert on the floor of the main tunnels behind Alice also has to be removed from the first tunnel, turned, and installed in the second.

As with the first stage of the turnaround, there are only centimetres to spare in the trench so it will be a very delicate and careful operation. "Turning a TBM of this size has only been done a couple of times before, and we expect there will be a world-wide audience watching the turnaround of the remaining gantries," Gliddon said.

Gliddon added: "The turnaround is expected to take 10 weeks and Alice will then be ready for her main drive south towards Owairaka to complete the second – northbound – motorway tunnel. Breakthrough at Owairaka is expected next spring."

The Waterview Connection project is planned to open to traffic in early 2017. It is being delivered by the Well-Connected Alliance which includes the Transport Agency, Fletcher Construction, McConnell Dowell, Parsons Brinckerhoff, Beca Infrastructure, Tonkin & Taylor and Japanese construction company Obayashi Corporation. Sub-alliance partners are Auckland-based Wilson Tunnelling and Spanish tunnel controls specialists SICE.

Both bores are 2.4km-long and are being excavated by the same 14.4m-diameter Herrenknecht EPBM. For the most part the tunnel route passes through sandstone and siltstone that varies in strength from 1MPa to 5MPa.