Work starts to stabilise landslide-prone stretch of State Highway 1 near Utiku

NZ Transport Agency Waka Kotahi has started work on State Highway 1 near Utiku to make a landslide-prone section of road more resilient.

NZ Transport Agency Waka Kotahi is completing work on State Highway 1 at Utiku, south of Taihape, to prevent delays and closures relating to landslides.

Beca senior engineering geologist Christoph Kraus said the active portion of the landslide was about 1km long and 400m wide.

“It’s a very deep-seated landslide; the larger movements are caused by these increases in groundwater levels that are associated with long-term, above-average rainfall,” Kraus said.

“We’ve designed a series of platforms from which inclined drains will be drilled in a fan pattern.

“Each inclined drain is about 100m long and is designed to intersect those water-bearing defects, thereby reducing the amount of groundwater that is able to get into the landslide.”

The drains have been installed between the road and the railway line – the first set dropped groundwater levels by up to 9m.

NZTA project manager Gareth Howie said there had been movements in the land through Utiku for decades.

“In late 2023, we saw some significant movement in the road and some cracks appeared,” Howie said.

“We found, through the investigation, the landslide was much wider than just localised on the road.”

Monitoring equipment at the site is helping workers understand how the area responds to rainfall and other conditions.

NZTA said it will keep tracking the equipment to help keep SH1 and the rail line open and safe.

Howie hoped the work, once completed, would give the local community and other road users a more resilient road corridor section.

“This implementation of this infrastructure and the monitoring going on means that we can add that resilience to the safety and the connectivity for that road and road users alike,” he said.

The next steps include installing tools to help NZTA monitor conditions on-site, and applying products to help stabilise the site, including shotcrete (sprayed concrete) over about 330sq m of the site.

There is no estimated completion date yet.