'Significant progress ' on Gorge repairs

Piling work is under way on the second slip near the Mangamuka Gorge summit. Photo / Waka Kotahi NZTA

Waka Kotahi NZ Transport Agency reported "significant progress on repairing State Highway 1 past the major remaining slip in the Mangamuka Gorge.

The installation of steel and concrete piles to support the road above the slip had been completed. The road was opened to holiday traffic for three weeks over Christmas, and closed again on January 10 so work could resume, since when another 16 piles have been drilled, completing the 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 1 of the repair, and there's still a lot more work required before we can open the road to traffic again," Northland system manager Jacqui Hori-Hoult said however.

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

Work had 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," Hori-Hoult said.

"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 had moved a few hundred metres towards the summit to a second slip, where the road surface had slumped by more than a metre. Twenty piles would be drilled to support the road edge so the road surface could be built up again. Installing the piles would 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," she added.

"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."

The final cost of repairs was estimated at $13.8 million.