Contractor Roads of National Significance

The making of the middle: Christchurch’s Western Corridor

There were a couple of complicating twists in what otherwise seemed like a simple four-laning of the middle of the three Christchurch Western Corridor projects. This is part two of a three-part series on this RoNs project by HUGH DE LACY.

WITH THE MEMORIAL AVENUE fly-over at one end, and the Western Belfast Bypass (featured in Contractor October) at the other, the four-laning of the Groynes to Sawyers Arms Road section of Christchurch’s Western Corridor upgrade looked the most straightforward of the three, with no bridges or fly-overs to worry about.

But there’s more to this $42 million widening of 3.67 kilometres of the Johns Road section of SH1 than will meet the eyes of the motorists travelling along it: The three projects comprising the Roads of National Significance each has its special challenges, and the middle one is no exception.

As well as the four-laning, Downer’s contract specified the creation of a single-lane service road for the 60-odd houses that front this section of Johns Road, a greenfields extension to an existing Christchurch City Council (CCC) access road, and the undergrounding and upgrading of all the utilities and services connecting the northern and southern sections.

Further, the middle section project had to skirt the edges of CCC’s old Rotokahutu landfill, and the McVicar sawmill site, highly contaminated like so many such sites around the country by copper-chrome-arsenic timber preservatives.

Unlike the projects to the north and the south which won’t be completed until 2018, the Groynes to Sawyers Arms Road section is in its last stages, and will add to the approximately 1.4 kilometres of finished four-laning between this project and the Russley Road/Memorial Avenue fly-over stretch to the south.

The central project being carried out by Downer Construction incorporates curbing and channelling of the whole stretch of four-lane, with the two carriageways separated by a median with wire rope barriers on both sides as well as in the middle.

Making-of-the-middle-770x470-4

The surfacing of more than 100,000 square metres has included stone mastic asphalt (SMA), open-graded porous asphalt (OGPA) and chip sealing, while the pavement construction has included 76,000 cubic metres of what project manager Mark Hurford calls “the Rolls-Royce of pavement”, foam bitumen stabilisation (FBS).

All this required the removal of surplus fill, but finding a convenient place to dump it was not a problem.

On the western side the extension to Greywacke Road, which gives access for the two big established businesses of McVicars Timber Group and Smith Crane and Construction, clipped the corner of the old Harewood landfill which, until the windstorm of September 2013, had been marked by a row of giant pines.

Because of the trees, the area had not been adequately covered at the time the landfill was closed, and when half the pines, the root-balls of which were founded directly in the landfill material, were flattened in the storm, it was apparent the area needed capping to prevent the waste material being exposed to public view along the new road.

Hurford and Downer suggested to CCC that the problem might be solved in everyone’s interests by clearing away the rest of the pines and covering the whole area with a cap comprising the clean waste from the road-forming.

“This proved to be very handy when it came to disposing of the surplus fill,” Hurford tells Contractor.

“We were able to cover the whole exposed area, about 800 metres by 100 metres, with about 1.8 metres of spoil, which served the dual role of stabilising the landfill and giving us a nearby dump site.”

Making-of-the-middle-770x470-2

The alternative would have been to cart the fill to either the Burwood or the Kate Valley landfills, at a considerable cost in transport and dumping fees to both Downer and the New Zealand Transport Agency (NZTA).

In the end, Downer was able to dump its 90,000 cubic metre fill, and the council to have its old landfill properly sealed for nothing.

Both sides of Johns Road presented access difficulties, for the residences on the eastern side and for McVicars and Smith Crane and Construction on the western.

The 1.4 kilometre Greywacke Road extension gives these two businesses access to the highway by way of the Sawyers Arms Road roundabout.

The extension’s carriageway is 12 metres wide, and includes a three metre wide shared-use path on one side, and a five metre wide stormwater swale on the other.

Though built by Downer for the NZTA, the Greywacke Road extension will end up being vested in the CCC.

On the eastern side of the state highway, a kilometre-long single-lane southbound service lane, accessed from Gardiners Road, was formed to separate the houses and the Harewood Crematorium from the highway.

The lane extends to Wilkinsons Road where it is serviced by a new roundabout off to the side of the highway, giving access to Johns Road by way of a southbound on-ramp.

Before the service lane could be completed, underground utilities had to be catered for, these comprising 2700 metres of water-main, 3500 metres of sub-main and 1400 metres of pressurised sewage installations.

As well as a service lane, the project provided each of the homes facing the highway with a choice of a new concrete or timber front fence.

A further complicating factor in the project was the need to deal with stormwater in an area where the water table is close to the road surface.

Infiltration trenches and dry ponds, lined with a mix of sand and topsoil, had to be constructed to contain the stormwater flow before it is filtered and discharged into the water table.

Topping the whole thing off by its completion date at the end of this summer will be additional pedestrian and cycle lanes, street lighting, and the undergrounding of power and telephone lines, as well as landscaping and fencing.

Hurford says the project is tracking ahead of schedule and budget, thanks to the commitment of a team comprising seven management personnel, 35 crew members and up to 55 sub-contracting staff.

For the past two years Hurford’s Downer team has shared its on-site premises with the project engineer and NZTA’s own project manager, something that has led to “a great relationship”.

“It has enabled us to introduce new staff to the client and gain their trust by setting high standards and delivering on our promises,” says Hurford.

  • In the next issue we feature the third part of this feature series: the Memorial Avenue fly-over. 

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