Welcome to the gateway to Christchurch

This article first appeared in Contractor magazine’s December issue.

The Memorial Avenue flyover is the gateway to Christchurch from the international airport, so it has to look impressive. HUGH DE LACY checks out the third of the Western Corridor projects.

AN ARCHITECTURAL COMPETITION, won by local firm Warren and Mahoney, has produced an iconic sculptural design in steel for Christchurch’s Memorial Avenue flyover, and a McConnell Dowell/ Downer joint venture (JV) has the task of building it.

The flyover, which carries SH1 over the Memorial Avenue/Russley Road intersection and facilitates the connection of the city with its international airport, will feature a four-legged arch curving gracefully 25 metres above ground level, with its two main beams crossing directly above the carriageway.

The painted steel arch is purely sculptural, and intended to welcome and impress visitors to a city recovering its vibrancy after the devastation of the 2010-2011 earthquakes.

And no doubt it will: at night the arch will be illuminated by $500,000 worth of creatively designed lighting.

The arch sits on four sets of piles, three per leg, which have been incorporated into the earthworks by a reinforced earth system that forms the main part of the flyover.

p36-Welcome-to-the-new-CHCH-300x300-2Called the Russley Road SH1 Upgrade, the project is the southernmost of the three Roads of National Significance construction projects currently underway to create a north-south corridor west of the city, from Hornby in the south to the Northern Motorway.

It’s a highly complex project involving not only the flyover and arch but three and a half kilometres of four-laning of Russley and Johns Roads – the one is an extension of the other, and they meet at Memorial Avenue – but also a second grade-separated access way to the Airport Precinct south of Avonhead Road, and an enlarged roundabout with a pedestrian and cycle underpass at Harewood Road.

The underpass at Harewood Road was completed and its opening formally welcomed in September by children from the local Harewood School who buried a stainless steel time capsule, made by harbour firm Lyttelton Engineering, to mark the event; a significant step in a project made all the more difficult by 33,000 vehicle movements a day.

Indeed, such is the complexity of the traffic control alone that the joint venture has already been awarded the NZTA’s “Keeping Customers Moving” category of its eight-category Going the Extra Mile (GEM) competition.

The flyover and arch comprise the project’s centrepiece, however, and provide the greatest challenge for traffic control.

To deal with it, the joint venture created what must be the country’s largest temporary roundabout – it’s actually more of an oval – 500 metres long, with north-bound traffic going around the western side, south-bound around the eastern, and the two joining at either end.

This has left a clear space in the middle for the construction of the grade-separated flyover which will see SH1 traffic go uninterrupted over the top, and airport traffic go underneath while controlled by two sets of traffic lights.

An underpass rather than a flyover was not an option for designer AECOM and geo-tech specialist Tonkin and Taylor because of the high water table, and the site being within the city’s water supply aquifer re-charge zone.

An underpass would have led to ongoing drainage problems, among other deterrent factors.

The flyover itself is supported by a steel Y-pier built by Napier-based Eastbridge, and the structure is future proofed to accommodate the addition of light rail, if the City Council eventually decides to go ahead with connecting the airport and the city by such a system.

While the welcome arch will be the most visible part of the project, it’s not the only element of art in construction: the Harewood Road cycle and pedestrian underpass features striking-looking pre-cast relief walls, produced by local company Cancast, to complement the equally impressive landscaping.

The underpass itself, by JV designer AECOM and architectural firm Jasmax, is a 150 metres-long box structure five metres wide by three metres high, with solar tubes penetrating the roundabout section of the roof for lighting.

Project manager Aidan Brannan tells Contractor that the construction of the underpass made rapid progress, with up to 12 metres completed in a single week.

p36-Welcome-to-the-new-CHCH-300x300“The local community, especially the school kids, were pretty thrilled to have their own special underpass opened, and they gave a kapa haka performance to celebrate it,” Brannan says.

“It really does look quite beautiful with those pre-cast relief panels and the striking colour system they’ve used.”

While elaborate structures have been designed for the Memorial Avenue and Harewood Road intersections, most of the others within the three projects underway along Johns Road will be serviced by roundabouts, and a couple of access points will be closed altogether.

Because they are too close to the Russley/Memorial flyover to be given separate connections to SH1, Avonhead and Wairakei West Roads will be closed and their traffic channelled over the main interchange.

Wairakei East Road will be connected to SH1 by off- and on-ramps, while traffic from the Wairakei Business Park is expected to use Wooldridge Road to access Harewood Road and SH1.

To this end NZTA, after consulting with the Christchurch City Council, has constructed a left slip turn lane and a traffic island where Wooldridge and Harewood Roads meet.

As with the Johns Road four-laning project to the north, the Memorial Avenue structure encroached on the old landfill that extends beneath the Christchurch Brevet Club and its feature Spitfire replica.

The old landfill was excavated and the material exported to the licensed disposal facilities.

This was part of a total cut of 180,000 cubic metres, and the wider project required a total of 250,000 cubic metres of fill, 4000 cubic metres of concrete and 130,000 square metres of pavement.

The McConnell Dowell/Downer joint venture has 28 staff currently on the project site, and at times, including subcontractors, there have been up to 130 people working on it.

The three projects of Christchurch’s Western Bypass are expected to be finished by Christmas 2018, after which those tens of thousands of daily traffic movements will travel at 80 kilometres per hour from Hornby, past the airport to link up with the 100 kilometres per hour traffic on the Northern Motorway just south of the Waimakariri River. 

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