The busy construction year at the NZ Transport Agency’s Waterview Connection project has ended with another huge milestone - the completion of all tunnel excavation works.
The tunnel team recently completed the excavation of the last of the 16 cross passages that connect the two motorway tunnels. The cross passages are about 11m long and will be used to evacuate people if there is an emergency underground, and to house equipment to operate the tunnels.
“To have completed so much tunnelling successfully and by the end of the year and without any major issues is a credit to the Well-Connected Alliance’s tunnel team,” says the Transport Agency’s Highway Manager, Brett Gliddon.
Tunnel Construction Manager, Chris Ashton says it has been a real team effort.
“It is a great achievement from everyone that there has been no discernible settlement or effect on people living above the tunnels. These cross passages have been built to world class standards with a very good safety record as well,” Mr Ashton says.
Excavating the cross-passages was one of the four distinct operations to construct the tunnels. The complex programme of works also included the work of Alice the Tunnel Boring Machine and the culvert gantry which was used for the smaller tunnel to carry services, as well as the first stage of the back-fill operation.
Construction began on 11 November 2013 when Alice started excavating the first tunnel. It ended just over 2 years later with the excavation of what is known as Cross Passage 2.
Although excavation is complete there are still many months of work ahead – constructing the road surface, installing concrete linings, lights, drains, the deluge safety system and signage as well as painting the ceilings and walls - before the tunnels can be commissioned for the planned opening in early 2017.
Meanwhile Alice, the TBM that successfully carved the twin 2.5km-long tunnels continues to shrink by the day.
Crews have been busy dismantling the TBM since she broke through from the Owairaka (southern) end of the tunnels in October.
In what is a technically difficult operation the huge machine is being taken apart in large sections, which are then lifted out of the trench and cleaned before they are shipped back to Herrenknecht, the German company that designed and built the TBM.
“Dismantling Alice has taken a lot of work and planning,” Mr Gliddon says. “The same ingenuity and accuracy that is the hallmark of the Waterview Connection is being used now to remove the machine.
“It’s a very tight fit to get some of these pieces out, sometimes there’s been as little as 200mm to spare.”
The giant 322 tonne cutterhead which carved through underground spoil to drill the tunnels has now been lifted out of the trench.
Six hydraulic jacks were used to push the cutterhead off the 184 studs that held it in place on the main drive of the TBM.
A 600 tonne and 300 tonne crane were then used to lift it out of the trench and onto a concrete slab where it was cleaned and separated into five smaller sections for transportation.
“Lots of people have asked us whether we can use Alice for other tunnelling projects in New Zealand, but each TBM is built specifically for one job. It’s designed to take into account the size of the tunnel and the type of material it’s boring through, which are individual for each project,” says Mr Gliddon.
The dismantling process is expected to be completed by the end of summer.
The Waterview Connection completes Auckland’s Western Ring Route, a 48km alternative route to SH1. It will link Manukau, Auckland, Waitakere and the North Shore, improving network resilience, travel time reliability and bus shoulder lanes as well as upgrading cycleway and pedestrian facilities.
The Waterview Connection project 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.