The Gorge will open for Easter

The Mangamuka Gorge was last opened to light traffic for three weeks over Christmas/New Year. Photo / Peter Jackson

State Highway 1 through the Mangamuka Gorge, closed by slips in July last year, opened for three weeks over Christmas, and will do so again next month for Easter.

Waka Kotahi Northland system manager Jacqui Hori-Hoult said last week that good progress was being made on repairs, and the road would be opened to light vehicles for four days, from Good Friday (April 2) to the following Monday, a public holiday.

Light vehicles would be able to travel in both directions in one-way convoys approximately every 15 minutes, from 8am to 7pm.

"Motorists will have to approach the convoys with some flexibility, as they won't run to a strict timetable," Hori-Hoult said.

"It will depend on how many vehicles turn up on the day, and people might miss getting on the end of a convoy and have to wait up to 30 minutes for the next one. The good news though is that they will get through."

Waka Kotahi understood the inconvenience to the local community, and the impact on businesses, of having to use the SH10 detour, which added time and cost to journeys.

"We opened the road for three weeks over Christmas, and we're looking for more opportunities to allow public access. If the Easter convoys work well and there's a demand, we'll open the road to convoys on most weekends after that," she added.

"There will be some weekends where the work is at a stage where it won't be possible for safety reasons to allow the public through the work area. We'll give 48 hours' notice of those weekend closures."

Meanwhile, heavy vehicles would have to keep using SH10.

Hori-Hoult said work to restore the road to two lanes by the middle of the year was going to plan, and had not been affected by Covid-19 lockdowns or bad weather. Most of the work crew were from Auckland, so had been operating on-site under alert level 3 conditions, working in bubbles with strict social distancing and hygiene measures in place.

Work was progressing at the site of the major underslip to install capping beams that tied together and stabilise the new pile wall supporting the road.

Earthworks had also begun, cutting into the bank above the road to widen it for two lanes of traffic. That section of hillside was historically unstable, so a 135m wall of concrete piles and panels was being constructed to protect the road. The wall would comprise 45 concrete and steel piles, each 15m long, with 2m or 4m panels inserted between them.

"The instability of the hillside above the road is one of the reasons we won't be able to open the road every weekend," Hori-Hoult said.

"As we put in the piles, we have to follow up with the panels to stabilise the wall. We can't leave the hillside exposed for long periods, like over a weekend."

Closer to the summit, piling on a second slip under the road, where the road surface had slumped by more than a metre, was scheduled to be completed last week. Twenty piles had been drilled to form a supporting wall, and a capping beam would be installed before the road surface was rebuilt and sealed.

The total estimated cost of the Mangamuka Gorge repairs was $13.8 million, including the ongoing slip repairs and the initial emergency response to July's storm damage.