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Source: New Zealand Transport Agency

Waka Kotahi NZ Transport Agency advises there has been significant progress on repairing State Highway 1 past the big slip in the Mangamuka Gorge.

The installation of steel and concrete piles to support the road above the slip has now been completed. The road was opened to holiday traffic for three weeks over Christmas and closed again on 10 January so work could resume. Since then, another 16 piles have been drilled, completing the total of 49 required to support and ensure the long term safety and stability of the road. 

“It’s been a great effort by the drill crew, but this is just stage one of the repair and there’s still a lot more work required before we can open the road to traffic again,” says Waka Kotahi Northland System Manager Jacqui Hori-Hoult. 

The next stage of the repair is to install capping beams that add to the stability of the pile wall. The capping beams are attached to the top of each pile with supporting cables drilled into the bank under the road. Once the road is rebuilt, the capping beams will be part of the road substructure. 

Work has also begun on cutting into the bank above the road to widen and restore the road past the slip to two lanes. 

“This is another complex part of the repair because of the old slip found above the road during our initial investigation of the storm damage last July. For the safety of our crews, we have to work carefully, monitoring the hillside to ensure there is no new earth movement.” 

Meanwhile the drilling rig has moved a few hundred metres towards the summit to a second slip under the road where the road surface has slumped by more than a metre. 

There will be 20 piles drilled to support the road edge so the road surface can be built up again. Installing the piles will take four weeks, with another four weeks to add capping beams. 

“As with the first slip, the drilling rig and other heavy machinery take up the full width of the road, so there’s no room for vehicles to pass during this phase of works.”

“At this stage we plan to have the road restored to two lanes by mid 2021, but it could be sooner depending on the weather and work progress. We’re constantly evaluating the work programme with our contractors to look for any opportunity to open the road at pre-arranged times to some vehicles”

“For now, we ask motorists and the local community to bear with us as we work as quickly as possible to complete the work. We will reopen the road in some form as soon as it’s possible to do so.” 

“Waka Kotahi understands the inconvenience to motorists of having to go via the SH10 detour route which adds time and cost to the journey, but we believe getting on with a permanent fix is the most desirable solution,” say Jacqui Hori-Hoult. 

The total estimated cost of the Mangamuka Gorge repairs is 13.8M. This includes the ongoing slip repairs and the cost of the initial emergency response to last July’s storm damage.   

While SH1 through the Mangamuka Gorge is closed, the recommended detour route to the Far North is SH10, which adds 20-30 minutes to the journey. Motorists are advised to plan ahead and allow extra time. 

For more on the Mangamuka Gorge repairs see https://www.nzta.govt.nz/projects/sh1-mangamuka-gorge-slip-repairs/(external link)

Piling work is under way on the second slip near the Mangamuka Gorge summit

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