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The late-April slip above State Highway 1 at the Brynderwyn Hills that has delayed reopening the vital route was so large that it will require roadworkers to move the equivalent of more than a quarter of the total amount of earth shifted during the project since February.
Due to the size of the slip, and the need for geotechnical assessments to determine the best approach to stabilise the hillside and ensure crew safety, Waka Kotahi NZTA says it cannot yet provide a reopening timeline.
The road was due to have reopened fully today, May 13, until an April 26 initial slip on a slope that teams were working to stabilise, followed by a larger one on April 30. The slips occurred on the hillside above the road at Kauri Tree Corner, about six kilometres south of the scenic lookout, bringing down thousands of tons of earth and trees.
NZTA project director Brynderwyn Hills Mark Ware says an additional 45,000 – 55,000 cubic metres of soil came down and now needs to be removed. To put that into perspective, the whole project thus far has entailed moving 180,000 cubic metres of soil.
Ware says that before the slip occurred, site monitors and geotechnical specialists had identified early ground movement, which enabled that section of hill and road to be cordoned off.
“We also have ground sensors throughout the area that provide early warning. This equipment is in place because we know that this area is susceptible to slips while the stabilisation work is ongoing.”
NZTA is now working with geotechnical experts to determine a safe solution.
“As a matter of course, our contractors undertake a review to see if there are lessons to be learned,” he says. “We have also brought in an independent geotech expert to support the team in evaluating our design and approach.”
As the review is ongoing, it’s too early to report results.
NZTA acknowledges that the setback has been disheartening – for its team as well as for road users eagerly awaiting the reopening of the road, which typically carries up to 15,000 vehicles daily. The stretch of SH1 has been closed since February 26 – excluding Easter – and traffic has been diverted to detour routes via Cove Road, the Paparoa Oakleigh Road, and SH12/SH14.
“Our crews have worked incredibly hard over the past eight weeks to keep the project on schedule and we were on track to open on May 13 until the recent slips,” Ware says.
“The recent slips show just how vital the recovery work is, so we can have a safe reliable route for Northland.”
