Alice, the huge boring machine constructing Auckland’s Waterview tunnels has disappeared underground on the first leg of her two-year, 4.8km-long journey from Owairaka to Waterview and back.
The 2,200-tonne machine, the 10th largest of its kind in the world, has now bored through 12 metres of soil and erected the first of the 2,414 reinforced concrete rings that will line the two tunnels.
The NZ Transport Agency’s Highways Manager for Auckland, Tommy Parker, says Alice started tunnelling three weeks ago and has advanced cautiously through a large block of soft concrete at the entrance to the tunnel.
“The alliance has deliberately taken the time required to ensure there is no risk to the structures around the tunnel portal.
“It’s also been important to temper the machine’s enormous power to prevent her from damaging temporary support structures as she entered the ground.”
Mr Parker says the caution has paid off, and both the machine and the structures have come through the launch successfully.
To construct the tunnel, the tunnel boring machine stops boring every two metres to lift the concrete tunnel lining rings, segment by segment, into position. Each completed ring is then grouted into place. Alice then continues her tunnelling, using the newly positioned ring from which to push off.
Mr Parker says Alice is currently boring at 40mm per minute compared to her top speed of 80 mm.
“She will get faster as more lining rings are installed. Each new grouted ring increases the stabilised length of tunnel giving a more stable tunnel behind to push against.”
When Alice started drilling through real dirt, it provided the first real test for the conveyor system that will remove 800,000 cubic metres of excavated spoil from the tunnels. The system takes the spoil by conveyor belt to bins in a building almost 1km from the tunnel portal. It sits in the bins for 24 hours before being trucked to a disused quarry being rehabilitated for industrial development.
The TBM operates 24 hours a day with crews of about 20 people. At least as many people are working in support of tunnelling operations such as the spoil conveyor system and batching plant for the grout used to cement the lining segments into place.
There will be a planned stoppage of tunnelling for several weeks in the new year for necessary work to prepare for the construction of the ventilation shaft building at the southern portal.
The Waterview tunnels are the key component of the NZ Transport Agency’s Waterview Connection project, being delivered by the Well-Connected Alliance, to join the South-western and North-western motorways (State Highways 20 and 16) in west Auckland and complete the Western Ring Route motorway.
Completion of the Western Ring Route is prioritised by the Government as one of its Roads of National Significance because of the contribution it will make to New Zealand’s prosperity by underpinning economic growth and sustainable development for Auckland and its regional neighbours.
The tunnels will each carry three motorway lanes, up to 45 metres below the suburbs of Avondale and Waterview and are due to open in early 2017.