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Kia ora and welcome to the May 2021 update from the Transmission Gully team.

Kia ora

Kia ora and welcome to the May update from the Transmission Gully team.

We are making great progress on paving and other finishing works. With only four months until the road is opened to traffic, we’re starting to reflect on the extraordinary effort that it’s taken to build this unique road. Numbers paint part of the picture!

Transmission Gully by the numbers (at road opening)

  • 27 kilometres long
  • Six years to construct
  • 11.4 million cubic metres of earth excavated/moved
  • 660,000 tonnes of aggregate brought to site
  • 104,000 cubic metres of concrete used.
  • 7,900 tonnes of reinforced steel used in bridges and other structures
  • Over 115,000 tonnes of asphalt laid
  • 25 bridges and large culverts
  • Longest bridge: Te Ara a Toa – 230 metres
  • Highest bridge: Te Ara a Toa – 60 metres
  • Largest cutting: Pouāwhā – Wainui Saddle – 70 metres high
  • 534 hectares of ecological mitigation and replanting (includes 2.5 million native trees and plants)
  • Eight streams modified/diverted
  • Over the course of the construction around 7,700 people have worked on site*

* Personnel figures include sub-contractors and everyone from ecologists to digger drivers to cleaners. If we included the people who have worked off-site (such as suppliers, designers and steel fabricators) the number would greatly exceed this.

Making kerbs. A spotter keeps the Slipform machine & concrete truck in sync. See the Slipform machine in action in the video further down in the newsletter.

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The streetlights are in at the Waitangirua Interchange

Carving its way through the hills. Looking north towards Te Ara a Toa, with the Transmission Lines in the background.

Upcoming construction works that might affect you

Streetlight Works – Mackays Crossing interchange and SH1 north of Mackays

Work has begun on streetlight installation in the northernmost section of Transmission Gully – around the Mackays Crossing interchange. This work will take around three months, with the team progressively moving from one work site to the next.

The team will start work on the SH1 shoulder near the northbound off-ramp (towards QE Park), drilling holes for the streetlights, and continue down the off-ramp.

From late May the work will move further north along the shoulder of SH1. To enable the team to work safely on the shoulder, we need to temporarily close one of the northbound lanes. For motorists this means a temporary extension to the single lane northbound, with the road widening to two lanes northbound around one and a half kilometres further north than it currently does.

In late June/early July the work will move to the other side of SH1. To enable the team to work safely on the southbound shoulder, we need to temporarily close one of the southbound lanes. For motorists this means the current southbound merge from two lanes to one lane on SH1 near Mackays Crossing will move north by around 325 metres.

There will be a reduced speed limit of 50km/h while the lane closures are in place.

Drivers should expect delays during peak travel times, particularly once the southbound lane closure is in place and the merge point moves north in late June/early July.

More detail will be shared on the Waka Kotahi Wellington Facebook page, and displayed on roadside messaging closer to the time of each phase of work.

Linden works

As we get closer to opening, we’re finishing work on the connection between Transmission Gully motorway and the existing SH1 at Linden. This means a change in the southbound road layout on SH1 near Linden so the team can complete earthworks and paving at the southern end of Transmission Gully.

When Transmission Gully opens this is where southbound traffic from the new motorway will merge with traffic travelling on the current SH1 (such as from Paremata).

Over the next few weeks, the median barrier will be shifted by up to six metres, reducing the area the team were working on in the median. This will enable both southbound lanes to be moved from the current alignment towards the median. There is no change for northbound traffic.

Works in the median strip at Linden – March 2021, getting ready to move traffic across to complete the southern end of the new motorway.

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Operating and maintaining the motorway

Concrete slab going down on the new TG Operations & Management building.

The slab is down, the frame is up… work has begun on the first and possibly the only permanent building to grace the Transmission Gully compound at Lanes Flat.

The building will house Ventia, the company that Wellington Gateway Partnership has subcontracted to operate and maintain Transmission Gully for the next 25 years.

Ventia is one of the largest essential service providers in New Zealand and Australia. It provides long term management of critical public and private assets and infrastructure.

The frame going up on Ventia’s new building at Lanes Flat, Pāuatahanui.

Once Transmission Gully opens to traffic, it’s Ventia’s job to operate the motorway 24/7. This will involve handling emergencies, traffic management and responding to incidents.

While any serious accidents will involve emergency services, if you break down on the motorway, one of Ventia’s incident response vehicles will come and help. It’s all part of the service.

Cameras will keep an eye on intersections, while stopped vehicles anywhere on the rest of the motorway will be detected by an ITS radar system monitoring traffic movement.

But just a note on that – Transmission Gully is a motorway so no vehicle should be stopping, unless it’s an emergency.

Ventia is also responsible for maintaining the integrity of the road and carrying out any repairs that come up over the next 25 years. That could be anything from fixing any damage to the median barriers to carrying out rehabilitation works and reseals to maintain the road in a good operating condition.

Transmission Gully has been designed and built to be highly resilient and safety will continue to be paramount.

The Ventia team will be carrying out regular inspections of structures and retaining walls, ensuring drains and culverts are clear and all streetlighting is working.

There’s also the environment to care for. The hard work carried out by the Transmission Gully environment and landscaping teams during construction will be continued. This means ensuring fences and environmental barriers are intact, vegetation is mowed and weeded, and predators are controlled, especially for ecologically protected areas.

With so much water in the hills, making sure the stormwater system is performing as designed is critical. Ventia has already established a water quality monitoring process. It’s just one of the ways Ventia is preparing for road opening.

Just another day in the office - Ventia inspects the fences and boundary up on the Gas Ridge line.

The company needs to expand locally and will be recruiting for a number of roles, everything from an Operations & Maintenance Manager to project Senior Supervisors to Field Staff. So, if you like the idea of a vocation with variety – responding to a traffic incident one day, mending fences the next – keep an eye out. The jobs will be out in the market very soon.

After 25 years Ventia’s contract with WGP (and WGP’s contract with Waka Kotahi) will end, and the road will be handed  over to Waka Kotahi in tip top shape; still as reliable as the day it opens.

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Slipform machine

At Transmission Gully we’re using a Slipform machine to create concrete kerbs and channels. The machine pushes concrete down into a mould where vibrators compact it into a uniform shape.

The Slipform machine has completed 26 kilometres of roadside drains on the motorway so far and is now making kerbs for the intersections.

Check it out in operation:

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Curious devices: The NDM and Benkelman beam

The Slipform machine is just one of the interesting machines helping build the road.

The little yellow box beside the worker in the centre of the photo above is a Nuclear Densometer (NDM).

It’s a scanning gauge that identifies the moisture, density and make up of materials or surfaces.

NDMs are used in civil construction, geotechnical engineering and the petroleum industry(external link), as well as for mining and even archaeology.

In our case, we’re using them to determine the density and moisture of every layer of the paving process (here the subbase pavement layer) to help us build a strong road.

The NDM emits a signal that is either reflected back by the paving layer or passes through it.

The device can only be used by someone with a nationally recognised qualification in materials testing who is trained both in the operation and safe practise of using the equipment. It travels in a special box in the back of a ute, away from the operator, with an ‘ionising material’ sign on the vehicle.

In this photo the engineers are setting up a device called a Benkelman beam to test the pavement deflection under the rear-axle load and tyre pressure of a standard test truck with dual tyres and a specific weight and axle set.  The measurement location is at the tip of the beam, between the dual tyres.

Here they’re checking the construction platform layer, which sits on top of the sub grade, for deflection. They are looking to see how much the pavement surface rebounds (i.e. moves up) when the truck moves away. Some flexibility is good. Too rigid and the pavement is brittle and breaks.

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Trucks at Mackays

If you’ve driven on SH1 near Mackays Crossing in the past few months you might have seen a lot of trucks lined up on the Transmission Gully site access road. The trucks are parked there when not doing the ‘quarry run’ – delivering aggregate between the quarry and the Transmission Gully site. The quarry run is generally on weekdays between 10am and 3pm.

The trucks are usually parked with the tipper tray slightly up so they don’t collect water.

Quarry trucks parked up on access road to the temporary asphalt plant at Mackays Crossing.

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Keeping you up to date

We continue to remind all members of the public to stay safe and not enter the project site at any time. Work is underway in multiple areas and it remains a high hazard area.

If you have any questions, please contact us at info@tg.co.nz. If you have an urgent matter, please call the 24-hour project hotline on 0800 TGINFO. If we are working outside of our normal work hours and you’re one of our neighbours, we’ll be in touch with you directly as usual.

In our next newsletter, we’ll share a new flythrough video. With so much paving activity onsite over the past few months the site will look really different to the last flythrough we filmed in February.

But for now, haere rā from the Transmission Gully team.

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We hope you enjoy reading these updates, and we’d love to hear from you. If you have any questions, comments or story suggestions, you can email them to info@tg.co.nz

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