“Get this done.”
That was the message taken to heart by the Waka Kotahi NZ Transport Agency team charged with fixing State Highway 1 through the Mangamuka Gorge.
It came from the local community, says project leader Norman Collier, and is the reason the road is not opening for Christmas or the summer holidays.
“Our message from the community is just ‘get this done’. We will get a lot more work done if we can stay closed.”
Staying shut for summer traffic means Collier is “very confident” the road will be open by May next year.
It’s been a tough time, whānau, but restoring our connection to the rest of New Zealand is just 12 months away. It’s a repair job that has attracted $100 million of funding, with Collier estimating another $60m-$80m will be needed before it is done.
Waka Kotahi gave the Northland Age an exclusive tour of the worksite for this special report on what is being done to repair damage to the highway.
Those who provided the tour - Collier and site supervisor and hapū intermediary Tomo Otene - are keen for locals to understand how much progress has been made, and how hard it has been to make that progress.
But it also came loaded with a recognition of how tough the road closure has been on the community, particularly with the August 2022 closure coming so soon after the year-long closure from July 2020.
By the time it opens, Kaitāia and further north will have been disconnected from the country, from whānau, business and work for close to three of almost five years that have passed since the start of 2020.
It started as a farm track
Collier and site supervisor Tomo Otene met the Age at the southern gate sitting across State Highway 1. From this point on, it’s hard hats and high-visibility vest across 13 kilometres of ruined road.
In summary, and there’s no nice way to say this, the road is rooted. Munted, even.
Nine months on from the big rains and heavy slips, there’s clearly a lot of work that’s been done. It’s also clear there is so much more to do.
It could never have been opened to allow single-lane traffic, even at an escorted crawl. The road is stuffed. We knew that, but seeing it is compelling.
And here’s Collier’s explanation for why: “The root causes of what we’re dealing with here is weather. And the other thing is history. It started as a farm track. It was never built to today’s standards.”
Otene: “For us in the community, we hear our kaumātua talking about being up here in their teens, seeing the elders pushing this road through.”
What began as a farm track turned into a road, first with metal and eventually tarmac. As traffic grew, so grew the road with bulldozers scraping a wider path.
Otene: “That’s how they did it through the whole country. Just bullies pushing dirt to the side.”
Collier agrees. He oversees a range of other projects, including the Brynderwyn Hills and Dome Valley. In these places, and probably throughout New Zealand, roads weren’t built - they evolved.
Those problems emerge almost everywhere on the job. He points to the banks along the roadside. They shouldn’t have a slope of greater than 45 degrees but most were about 60 degrees.
“It’s just too steep.” Shaving the banks back to 45 degrees wasn’t an option because you would take the top off the Mangamukas before you were done.
More traffic, more rain, more complications atop a roading network that was never really developed beyond its rough roots. That has become increasingly apparent as Waka Kotahi digs deeper into the site and learns more about its history and what the future will bring.
Being proactive
It means there has been a focus on preventive work. Having seen what nature can throw at the gorge, there’s anticipation of more and maybe worse to come and no desire to suffer a fresh setback, such as happened in August when the road was closed again.
“We want to stop being reactive. We want to get ahead of it,” says Collier.
That has included improving drainage across the stretch of highway, even beyond the repairs that were done in 2020-21.
Otene sits for a photograph with the previous repairs in the background. “There’s been lots of questions about whether this had gone,” he says, looking back at the decorated concrete wall holding back the hillside.
It’s still there - largely, the modern works from 2020 to 2021 survived the extraordinary weather thrown at Mangamuka since August last year.
But the work crew learned from it, too. Drainage pipes have increased in size from 350mm to 800mm. Extensive catchments have been built to catch water coming off the hill and roadside drains sculptured to carry it away from the places it has caused the worst damage.
The outflow pipes carrying water under the road now stretched far out into the bush where water previously dropped almost immediately next to the road, contributing to undermining.
When it rains, Otene listens to it hit the roof of his Mangamuka home and worries about how much damage is being done up the gorge. It’s a house built 30 years ago and used only as a holiday house when returning from work in tunnels in Australia.
He came back initially to work on Auckland’s CRL project and then was lured north by the prospect of proximity to his roots and the puzzles offered by the Mangamuka project.
And this is a feature of the Mangamuka repair often mentioned. As Collier describes, there is nothing simple about the repair job.
There are 26 separate slips of which six are considered “critical”. “These are the ones that are susceptible to movement with heavy machinery,” says Collier. Every one of those slips poses a particular technical challenge.
Many puzzles to solve
The Mangamuka Gorge is one big engineering Rubik’s Cube. We were joined by Kurt Grant, a veteran of complicated construction projects, who describes it like this: “There are different puzzles to solve at every place. It’s not all the same thing.”
The slips appear to have occurred in three ways, which, collectively, cover every kind of headache possible.
There are those that have come from above to cover the road and those that have occurred below and eat away at soil under the road. And then there is also a site where the slip is happening above, on and beneath the road - one big chunk of hillside that’s threatening to embrace gravity.
At the major slip areas, there is a pattern to the work that is being done.
The first step has been to stabilise and strengthen the road surface in anticipation of bringing in heavy machinery needed to make the permanent repairs. That machinery will weigh as much as 60 tonnes and will shake and vibrate as it works, requiring as solid and level a surface as possible.
To make those intermediate fixes, 600mm pipes are forced down as much as 20m, filled with concrete and long steel beams, locked into a concrete step at the base. They sit along the roadside at regular intervals. Tomo reckons they’ve been doing five or six a day with 700 needed across the whole site.
Those foundational elements need support, which comes in the form of steel cables secured back under the road and into the hillside. “Like a cable holding a tent peg,” says Collier.
And there is further support with a steel rebar cage that sits across the top of the pipes locking them into place.
Remember, these are the steps that need to be taken so the proper work on the road begins. Collier says: “It’s getting enough strength in our road so we can bring big piling rigs in. We’re basically building 20m-high walls. Working both sides, we first need to build a stable platform to work from and then bring in the big stuff.”
In a way, what comes next is a repeat of the intermediate steps but with much larger pipes - a shade over a metre - plunged much deeper into the earth. It is like building a complex and enormous retaining wall.
Safety for workers
Dotted across the hillside across the worksites are poles driven into the ground topped with solar panels. They pick up movement on the hillside, and water pressure, with the results transmitted to a system that communicates safety levels to boxes with blue, amber and red lights.
It means every worker is able to see the prevailing safety condition - blue means work on, amber means special permits needed, and a red light means it is too dangerous to work. As Otene explains, there’s no situation where risk suddenly changes and people are running for safety because the warning system is continuous, providing plenty of notice.
At some sites, those sensors recorded movement long after the rain had stopped. At one particularly complicated area where the slip encompasses the entire area above and below the road, the whole hillside including the road has been measured moving day after day.
At that site - and others - there is so much soil gone from under the road that the tarseal has sheared away offering a view of stratified repairs over time. Pointing to one, Collier says it is a thicker road surface than would otherwise be expected and probably reflected repeated repairs as the road repeatedly slumped with soil subsidence over the years.
Abandon option ditched
The repair job might not have happened. Collier says there were options for an alternative route, although he dodges questions on precisely where that might have been.
Not doing the work was also considered. “One of our options was actually to abandon this route.” It was taken to Waka Kotahi’s board but the idea of doing so was rejected because of the impact on business and the community and state highway resilience.
“For the medium term [he says up to 10 years] there wasn’t another solution. In terms of long-term, it would be to build a complete new road in the North.”
“You would be looking at figures in the billions for that. As much as people don’t want to hear it - and it’s the truth - we’re sitting in a country that only has so much money.” It is about doing the most possible with the funding available.
And even recent events have widened the idea of what is possible. “Weather events provide an opportunity to do a lot of projects that might not otherwise be done.”
Untapped workforce
A large part of Collier’s optimism around finishing in May was the staff attracted to work. There are those - like Otene - who were compelled by the complexity.
“This is an extremely complex, technical job. Its complexity has attracted the [human] resource. There’s a bit of excitement in doing something really hard.”
And then there are those who were already here. Collier said 60-70 per cent of the 100 people working on the project were local. Such was the response, it has left him convinced there is an untapped workforce in New Zealand that can be drawn on for projects such as the Mangamuka recovery.
“People want to be part of the recovery. I get two-three hours of extra production out of my workers because they live just down the road.”
And it goes further than that. Otene has hunted this bush for decades. With local hires, there will be others with a similar attachment.
Collier: “I’m very confident. I really mean it when I say I’ve got an awesome team up here. The site culture is underpinning the process.”
