Waterview Connection: First stage of tunnelling to stop

Alice, the tunnel boring machine. Photo / NZTA

The first stage of tunnelling the second tunnel on Auckland's Waterview Connection project will stop today.

The Waterview Connection project involves construction of twin tunnels and an interchange to link the Southwestern and Northwestern Motorways.

It will complete Auckland's Western Ring Route, a 47-kilometre-long motorway between Albany on the North Shore and Manukau in the south.

The pause in tunnelling had been planned in order to enable the turnaround of machinery needed to allow the project's tunnel boring machine, dubbed Alice, to finish construction of the tunnel, NZ Transport Agency's highway manager Brett Gliddon said.

"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."

Alice completed excavation of the project's first tunnel last September, travelling 2.4 kilometres north from Owairaka to Waterview.

The front section of the machine, including the cutter head, was turned around before Christmas and has already excavated 270m of the second tunnel.

"There is now enough room to bring all the necessary gear into the tunnel so that we can complete the job," Mr Gliddon said.

The turnaround will be complex as a temporary gantry which had been assisting the machine has to be removed and two remaining gantries which contain important services for the operation of the machine have to be pulled from the first tunnel, turned 180 degrees inside the trench and then reconnected to the cutter head.

"That's about 50 metres of machinery - half the length of a rugby field," Mr Gliddon said.

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.

Two access bridges will also have to be built in the trench to connect the tunnels.

There were only centimetres to spare in the trench so the operation would be delicate, Mr Gliddon said.

Turning a tunnelling machine of such a size was rare and Mr Gliddon said he expected there would be a world-wide audience watching the turnaround of the remaining gantries.

The completed motorway will give drivers a second motorway choice to the Southern and Northern Motorways (SH1) through central Auckland.

The Waterview Connection project is planned to open to traffic in early 2017.