It’s all changing at interchange

An ‘army’ of earthmovers is remoulding the landscape in preparation for what will be a much improved highway interchange. RICHARD SILCOCK takes a look at this comparatively fast moving project in the Hutt Valley north of Wellington.

THE OFTEN ACCIDENT prone intersection of State Highway 2 and State Highway 58

An artist’s impression of the completed interchange, looking north, showing the dual carriageway of SH2 running through the centre with the on/off ramps to the elevated interchange for SH58 (running up the hill to the left) and Manor Park, the railway line and Manor Park Station on the right.
An artist’s impression of the completed interchange, looking north, showing the dual carriageway of SH2 running through the centre with the on/off ramps to the elevated interchange for SH58 (running up the hill to the left) and Manor Park, the railway line and Manor Park Station on the right.

(Haywards Hill) north of Wellington was again recently highlighted with another accident hitting the news. However, with construction work well underway for an elevated roundabout to replace the SH58 and Manor Park turn-offs and the traffic lights on SH2, accidents should be a thing of the past.

Following a turning of the sod ceremony last November by the Minister of Transport, Simon Bridges and the mayor of Upper Hutt, Wayne Guppy, earthworks and construction work began in earnest in early March this year and have been rapidly progressing with land contouring, construction of abutments, stormwater pipes, retaining walls, cycleway underpasses, and the foundations for the new roundabout commencing in late April.

Downer New Zealand is the contractor for the project, with Aurecon and Tonkin and Taylor providing the design for the New Zealand Transport Agency under a $43 million design and construct contract.

Project manager for the work, Iain Fletcher, says the main feature of the interchange will be the elevated roundabout which will allow an uninterrupted flow of traffic along SH2.

“The new interchange will be grade separated and consist of an elevated roundabout over the existing SH2,” says Iain. “This will allow traffic heading north and south to flow freely and not have to stop for traffic lights. The traffic diverting to SH58 [Haywards Hill] or to Manor Park will take off-ramps at the side and at both ends of the interchange and enter the roundabout before proceeding on to their destination route.”

The current flurry of earthworks being carried out by Downer and subcontractor Burgess Crowley Civil will see around 200,000 cubic metres of earth shifted by late this winter. This work is being carried out using an array of bulldozers ranging in size from D4 to D6, along with five- to 37-tonne excavators and scrapers. Additional material is being brought to the site by truck and trailer units and compacted by several 12-tonne vibrating single drum rollers. Due to the exceptionally dry weather conditions experienced over summer, dust is being suppressed by watercarts constantly working around the 20-hectare site.

“A lot of the earthworks have involved cut-to-waste material, such as peat, organics and saturated silts, which are unsuitable as fill,” say Iain. “Cut-to-fill granular rock is being supplemented by rock from nearby local quarries, with the general fill material from one quarry and the structural fill from another. This is working well as it eases the pressure on the quarries to achieve the production and delivery times we require to maintain our schedule.

“In some cases we’ve pre-loaded areas where there is deep-seated compressible peat. To achieve this we have placed three metres of surcharge material in these areas and expect to have the required amount of consolidation by September this year.

“Work on the abutment supports for the two roundabout ‘bridges’ is also progressing well and is tracking well ahead of our programme,” says Iain. “These abutments comprise four reinforced earth walls faced with concrete panels. The panels have been cast on-site by Hutt Concrete Products, who are locally based and our team are constructing the walls.”

Cont-1606-Project-Interchange-300x300 copy
Top: Drone view of construction site, with cycleway underpass (foreground) and 1800mm in diameter Dry Creek concrete storm water pipe under construction. Also visible is a mound of compression material (centre), SH58 (left) and SH2 to the right.

There are four reinforced earth walls in total, each with two return walls at each end. When completed they will be six metres above the four-lane SH2 carriageway.

SH58 itself is being widened and a number of tight corners are being taken out (refer Contractor October 2015), and at the interchange with SH2 will comprise a grade separation between the north- and southbound lanes.

“We will achieve this by a series of retaining structures comprising reinforced earth walls and geogrid reinforced earth embankments,” says Iain. “This will allow us to accommodate the changes in the ground contours.”

As the site, which rises relatively steeply on the western (Haywards) side, is bisected by Dry Creek Gully, stormwater from the gully is being piped via an 1800mm diameter stormwater pipe to the eastern side. An existing box culvert, which conveys water from another stream under SH2 is also to be extended at both ends to allow for the on and off-ramps. Rain water will be drained from the highways via kerb and channel to collector stormwater lines, which will be up to 750mm in diameter.

A combined pedestrian and cycle overbridge to the north of the interchange will connect the railway station at Manor Park on the eastern side of SH2 to a new park-and-ride car park, which is to be constructed as part of the project, and the walkway to the Belmont Regional Park on the western side.

The overbridge will be constructed using a combination of in situ and precast concrete materials and will include urban art features on the fascia that are in keeping with the local environment. Micro-piling for the ramps leading to this bridge is complete and pile cap construction has commenced for the bridge itself.

A new cycleway in both the northbound and southbound directions will also be constructed as part of the interchange development. The cycleway will pass under the highway’s on and off-ramps via four underpasses.

NZTA central regional director Raewyn Bleakley says the new interchange will not only improve safety at the intersection but also improve journey times for traffic heading north/south on SH2, or west to Porirua and the Kapiti Coast on SH58.

“This multifaceted project will also make a real difference for travel choices and help remove barriers for people using alternative forms of transport,” says Raewyn.

While the project faces a tight timeframe and is being constructed over a busy stretch of highway, the interchange is expected to be completed by June next year.

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