Q: How are they forming a level road surface within the circular tunnel? Do they just build it up with fill or are there cavities, pipes etc under the road surface for utilities, services or drainage etc? If trucks are using the tunnel to take away the spoil, presumably they have a level surface to drive on? Glenn Clark, Auckland.
The NZ Transport Agency says material from the tunnel excavation is removed by conveyor belt linked to the tunnel boring machine, Alice. This leaves a completed, fully lined empty tunnel. Following Alice is a culvert gantry - a machine to build a smaller "tunnel within a tunnel". It puts large concrete segments shaped like an upside-down U on the larger tunnel's floor. This culvert will house most services to help operate the tunnel. The top of the culvert is being used as a temporary road until the sides of the culvert are backfilled with aggregate. A further 1.5m or so of fill and paving will bring the surface up to road level wide enough to carry three lanes of traffic when the two tunnels open in early 2017.
Q: Can you please give an update on the Waterview progress? Christine Jamieson, Sandringham.
Construction stopped on February 20 so machinery could be turned around, with just millimetres to spare.
Alice will then be ready for the drive south towards Owairaka to complete the northbound tunnel. She will be stopped again after travelling far enough so the rest of her mechanical entourage can be connected again behind her. One gantry will be removed and two others pulled from the first tunnel and turned 180 degrees before being reconnected to the cutter head. The gantry being used to build the services culvert on the floor of the main tunnels behind Alice also has to be removed, turned, and installed in the second tunnel.
Alice is due to resume full tunnelling again this month and complete the second of her 2.4km-long underground journeys next spring.
