Source: New Zealand Transport Agency
The most direct route through the Far North is now open to all vehicles except those over dimension, with extensive repair work on State Highway 1 in the Mangamuka Gorge almost complete.
“People driving through will be able to see first-hand the amount of remedial work carried out including our 135m long 4m high retaining wall. But we encourage road users to drive carefully as the road alignment has changed and road shoulders have been reshaped,” says Jacqui Hori-Hoult, Waka Kotahi Regional Manager Te Tai Tokerau me Tāmaki Makaurau.
While Waka Kotahi will be allowing vehicles through from 6pm on June 30, temporary traffic management will be in place for a small section of the gorge where it will be reduced to one lane, so crew have enough space to be able to finish work on the largest retaining wall.
A one in 500 year storm event in July last year caused the damage to the state highway and prompted an urgent response.
Eight slips were identified with the largest (site eight) in imminent danger of causing the road to entirely fall away.
“It was under tough conditions that our team took on the challenge to restore this important connection. As they worked, they needed to continually monitor the hillside to ensure there was no new earth movement,” says Jacqui Hori-Hoult.
Site eight was where the most complex work was undertaken. Significant strengthening was required with 49 concrete and steel piles inserted into the hillside to stabilise and support the road below, and the same number inserted into the hill on the other side of the road as part of a retaining wall to prevent the earth above from slipping down. The wall will help future proof this section of state highway.
“While site eight was the most complex, each of the damaged areas have presented different challenges with work often being carried out in narrow corridors or on steep terrain,” says Jacqui Hori-Hoult.
“We have worked hard to ensure the new infrastructure fits within the environment it sits by choosing natural colours for our retaining walls which reflect the surroundings as well as using native, locally sourced shrubs in our replanting work.”
Travellers and locals have been allowed through Mangamuka Gorge on several occasions while work was paused for public holidays, however, Waka Kotahi appreciates that the closure has been an inconvenience.
“We know the detour route has significantly impacted travel times, especially for the freight industry, we want to thank all road users for their patience and understanding. Given the importance of this connection it was crucial we not only carried out repairs but also installed drainage works to limit damage from future weather events,” says Jacqui Hori-Hoult.
While the road is now open, crew remain on site planting to reduce future erosion and finishing above and below ground drainage so that stormwater is drawn away from vulnerable areas.
The finishing touches are also being carried out on the longest retaining wall crew placing an anti-graffiti spray on the wall, after a design created by Ngāti Kahu is stencilled on.
For more information on the project:
SH1 Mangamuka Gorge slip repairs
Fun facts
- Nearly 200 people worked on the project
- Almost 8,000m3 of dirt fell away from site 7 & 8 down to the river
- 800m3 of concrete poured at site 8 – (a concrete truck holds 6.0m3)
- There are five retaining walls through the gorge, the largest is 135m long and 4m high
Videos
Downloadable grabs and b-roll available – YouTube links below:
Previous progress videos:
Stills
SH1 Mangamuka Gorge slip repairs photo gallery
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