Ask Phoebe: Dennis there for the heavy lifting

'Alice' the tunnel drilling machine Photo / Greg Bowker

Just recently I have noticed a huge new piece of machinery - a gantry perhaps - near where the Waterview tunnel is being built, at the Waterview end. What is it? It looks like the one that was used on the Newmarket Viaduct. Can you help please?

Leonie Parsons, West Auckland

It seems that Alice, the tunnel-boring machine beavering away underground in Waterview, has a new friend. It is, as you surmise, a gantry. It (he?) is called Dennis, so named by project workers in honour of a workmate who died last year from cancer. It is painted yellow to promote the work of the Cancer Society, the charity supported by the Well-Connected Alliance constructing the tunnels.

Dennis will become more obvious in the next fortnight or so when it moves out over Great North Rd.

It is 98m long, weighs about 140 tonnes, and is similar to but smaller than the blue gantry used recently to construct the replacement viaduct at Newmarket.

The four interchange ramps to connect the Northwestern and Southwestern motorways involve the building of 1.7km of bridge structures. It requires placing 270 precast concrete beams, each up to 37m long and weighing up to 65 tonnes, to create the 53 spans for the four ramps. The spans will, in turn, support the deck structures.

The first ramp being built will take westbound traffic from the Northwestern Motorway to the southbound tunnel. This is the route you will be able to use to get from the CBD to the airport.

The gantry was designed and built in Italy specifically for the Waterview project.

It was chosen over conventional bridge construction methods to minimise effects on adjacent archaeological areas and traffic flows.

Dennis began work two weeks ago and will shortly switch from day to night shifts, with closures on the road directly below the lifting mechanism. The first closures are scheduled for mid-March and will affect traffic only leaving Great North Rd to go west.

Information about road closures relating to the gantry's operation will be provided by electronic road signs, advertising and the NZ Transport Agency's traffic information.

The project's tunnels will each carry three motorway lanes, up to 45m below the suburbs of Avondale and Waterview, and are due to open in early 2017.