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Construction update

Welcome to the April 2019 construction update

Here is the latest from the team on what’s been happening across the Southern Corridor Improvement Project and what’s coming up.

Southern Motorway at Pahurehure 

Southern Corridor Improvements Projects progress

As the SH1 motorway upgrade between Manukau and Papakura progresses, motorists are starting to benefit from the improvements.

Motorists using the new, much longer (700-metre) northbound Takanini loop on-ramp are reporting a significant improvement in travel times and convenience, with better traffic flows delivering a more reliable commute for regular motorway users.

The new Takanini Interchange northbound on-ramp has already delivered time-saving progress

Progress on Pahurehure Inlet bridge

Work is continuing at pace on the new replacement causeway bridge spanning the Pahurehure Inlet, but motorists might never notice the extensive work going on under their wheels as traffic flows are maintained throughout.

The original bridge, built in the 1960s, was only 11 metres long and was made up of two two-lane bridges. But modern motorway use, updated earthquake standards and the greater load of two extra lanes to widen the motorway meant that the bridge needed to be redesigned and completely reconstructed.

Construction began in 2017 with the addition of two 60-tonne beams next to the existing Southbound bridge. These allowed the diversion of all motorway traffic on to the Southbound bridge.

The old Northbound bridge was demolished in 2018 and replaced with a single 30-metre span across the inlet, sitting one metre higher than the previous bridge. Both directions of traffic were diverted onto the newly constructed half of the bridge in November 2018.

Extensive work has been undertaken in the first quarter of 2019 to protect the sensitive coastal marine environment during the demolition of the old northbound bridge and in preparation for the final construction stage.

This widening has enabled an improvement to tidal flow under the bridge using retaining walls and revetment (coastal edge protection) rock from locally-quarried basalt. The revetment provides habitat for the diverse marine life thriving in the inlet as well as protecting the shore line from coastal erosion. A family of ducks, two shags and a heron have made their home in the surrounds and often visit the work site or fish nearby.

Local resident

New bridge beams will be lifted into place by cranes in early May, forming the new bridge deck for the final stage of the permanent bridge. Bridge deck construction and surfacing will continue through to August, after which Southbound traffic will be switched over to the new half, creating a centre median work zone.

Modern, solid concrete median barriers will then be constructed through the median strip using ‘slipform’ methods (described later in this update). The completed bridge will allow for three lanes of traffic and a 3-metre-wide shoulder in each direction.

The new bridge will be fully open by November 2019.

The 30-metre span of the new motorway bridge, with rock revetments to protect the waterway. A shared user path is being constructed alongside the motorway, shown here on a separate bridge.

Stormwater retention wetland underway at Takanini Interchange

 

Stormwater treatment and retention development at Takanini Interchange

Protecting the natural environment from stormwater runoff is one of the environmental goals of the Southern Corridor Improvements Project.

A new wetland is currently being excavated in the shoulder of the Takanini Interchange, where a large pond is being built to collect rainwater. Once the excavation is complete, the site will be planted with plant species that filter out dirt and contaminants from the motorway runoff water before it makes its way into the stormwater system and local waterways.

Local native plants are ideally suited to the damp conditions and species to be planted include Oioi, Toetoe, Rautahi, Wiwi and Ti Kouka.

The planted areas will look a little bare at first but will grow to enhance the green motorway corridor, as well as providing a natural habitat for insects and wildlife.

Botanic Gardens gets environmentally-enhanced motorway boundary

The hugely popular Auckland Botanic Gardens in Manurewa are getting an unexpected bonus from the Southern Motorway development, with the provision of new, 5-metre-high, planted retaining wall along 200 metres of its motorway boundary.

The work provides drainage and stabilises both the new motorway lanes alongside the Gardens.

Underneath the motorway shoulder created by the works sits a sophisticated, stepped Terramesh system, topped with fill, topsoil and a carpet of matting. The matting provides a base for planting, which will begin next month. In time, the retaining structure will become a green wall.

Once the scaffolding comes off, the new southbound motorway shoulder (just prior to the Hill Road off-ramp) will be completed, paved and surfaced and a solid concrete barrier will be installed along the edge.  Work in this area is expected to be completed by late August 2019.

Retaining wall on the motorway boundary of the Botanic Gardens

Slipforming efficiency for safer, modern median barriers

As you drive along the Southern Motorway, you can expect to see workers and machinery inside the centre median strip, between the Southbound and Northbound lanes. They’re building safer, solid concrete median barriers that will provide greater protection from oncoming traffic. And they are casting them in-situ, as they go, using a process called “slipforming”. The new barriers have a core of steel cables, around which the concrete is cast. The new centre barriers are being built along the whole Southern Corridor Improvements Project, and in some places along the edge of the new motorway shoulders.

Slipforming solid concrete barriers on the Southern Motorway

For further information

If you have any comments, suggestions or feedback, please contact us via email southerncorridor@nzta.govt.nz

We hope you have enjoyed this construction update and we look forward to letting you know more about the construction works for the southern corridor.

If you have any questions or queries, please contact our team on free phone 0508 NZTA SCI (0508 6982 724) or at southerncorridor@nzta.govt.nz. And feel free to visit us at the Project Office located at 8-12 Great South Road, Takanini.

 

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