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Managing progress at Waterview 4 March 2015

Peter Kenyon, TunnelTalk

The mega-TBM excavating the NZ$1.4 billion Waterview motorway tunnels in Auckland, New Zealand, is on a 10-week break while the remaining pair of back-up gantries are attached.

Removing back-up gantry from the completed first bore
Removing back-up gantry from the completed first bore

The 14.5m Herrenknecht EPBM, Alice, completed the first of two parallel 2.4km drives in September last year (2014) for the Well Connected Alliance comprising main construction contractors McConnell Dowell, Obayashi and Fletcher, and the New Zealand Transportation Agency (NZTA). Following a complex turnaround operation within the narrow confines of the 39m x 25m trench at the north portal (the northern approach trench), the machine was advanced 300m before making a scheduled stop at the end of last month (February 20) to manage reattachment of the remaining two of three main sections of back-up gantry.

Due to space restrictions in the trench, those two sections had remained inside the completed northbound tunnel while the turnaround of the TBM was managed. The machine was then driven into the southbound alignment with only the first section and a temporary section of back-up gantry attached. The temporary back-up is now being removed.

In all, the stoppage is scheduled to last 10 weeks, with tunnelling still on course to achieve final breakthrough at the south portal in Owaikara in Spring 2016.

Meanwhile, excavation of the 16 cross passages, spaced at 150m intervals, in under way and on schedule for completion by the end of this year (2015). Cross Passage Manager, Alistair McPhee said: “Our cross passage team has made a solid start to 2015, completing the installation of ground support for the canopy tubes in cross passages 2 and 3. During February we will be installing more of these tubes in cross passages 14, 15 and 16.”

The canopy tubes provide a temporary ground support for the cross passages before temporary shotcrete lining is applied and permanent concrete is poured. The team aims to erect three lots of 12m canopy tubes per dayshift.

“We have also done a lot of investigation drilling from cross passage 2 to 16 (southern end to northern end) with one more set to be completed when the culvert gantry moves into the northbound tunnel,” said McPhee. The culvert gantry is a specialist, self-propelled back-up that manages installation of the 2m x 3.7m x 2.22m U-shaped precast concrete culvert sections behind the TBM and under the road deck. “Drilling allows us to check the ground conditions including geology and possible water inflows," said McPhee. “This helps us understand any problems we may encounter before we excavate.”

The Waterview Connection project is planned to open to traffic in early 2017. It is being delivered by the Well-Connected Alliance comprising the New Zealand Transport Agency and main construction contractors McConnell Dowell, Obayashi of Japan and Fletcher Construction. Other partners in the project are Parsons Brinckerhoff (design), Beca Infrastructure and Tonkin & Taylor, alongside sub-alliance partners Wilson Tunnelling of Auckland and Spanish tunnel controls specialists SICE.

“Like the first stage of the turnaround, there are only centimetres to spare in the trench so this is a very delicate and careful operation,” said NZTA Highway Manager Brett Gliddon. “Turning a TBM of this size has only been done a couple of times before and we expect there will be a worldwide audience watching the turnaround of the remaining gantries. The team has already shown great skill and innovation, and we anticipate the operation will go smoothly.”

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