In October 2024 we completed the longest and most complex single-span bridge we have ever built, in the most difficult terrain we have ever faced. We set about designing an innovative, lightweight solution that would overcome all obstacles and allow both stock and farm machinery to get across the 50m ravine (rated to 0.35HN).
Location
Wairoa
Client Name
Te Whakaari Incorporation
Date
October 31, 2024
Related
Remote locations and challenging access are never barriers to building a bridge that will unlock greater productivity and efficiency on your land.
In October 2024 Bridge It NZ completed the longest and most complex single-span bridge we have ever built, in the most difficult terrain we have ever faced.
The fact it was a resounding success is thanks to our team’s expertise, determination, professionalism and ability to adapt to even the toughest environments.
Tukemokihi Station lies in the rugged and remote hills between Gisborne and Wairoa. This 6200ha sheep and beef farm is owned by Te Whakaari Incorporation (a Māori land trust), and for over 100 years an old suspension bridge provided safe passage for stock to reach the western side of Tukemokihi Stream. But a severe storm in mid-2022 toppled a large macrocarpa tree onto one of the bridge supports, cutting access.
“When our old suspension bridge collapsed, we pondered whether or not to replace it,” admits Te Whakaari Incorporation Farm Supervisor, Hilton Collier.
“We knew there was a whole lot of environmental regulation that we would be faced with, so we wanted to assess how much of a priority that bridge was in terms of access to almost 2000ha. We did have another route but it probably added a day’s mustering every time we had to move stock to that part of the farm. We lost a lot of operational efficiency, functionality and productivity because we didn’t have a bridge.”
Bridge It NZ had previously built a bridge on the neighbouring station so they were asked to take a look.
What awaited our team was an unprecedented challenge.
Not only was the farm remote but the terrain was incredibly steep, with access via numerous hairpin bends and narrow load-restricted bridges, complicated by overhanging trees and large slips caused by Cyclone Gabrielle.
Just as problematic was the soft sedimentary papa rock which proved to make ground conditions exceptionally slippery and dangerous.
It simply wasn’t possible to truck in a pre-fabricated bridge and crane it into place like we usually would. Large components and machinery would never make it to site.
Instead, Bridge It NZ and our partner, Tiaki Engineering, set about designing an innovative, lightweight solution that would overcome all obstacles and allow both stock and farm machinery to get across the 50m ravine (rated to 0.35HN).
“Bridge It NZ were willing to give us a solution for what we were trying to achieve,” Hilton explains. “If we had gone to a larger national firm, we probably would have got something the size of Transmission Gully with the price tag to match. We wanted a crossing that we could drive a farm ute or motorbike over, that we could use as a stock crossing, and that met all the health and safety parameters necessary to keep everyone safe.”
With a 16m drop to the riverbed below, Hilton describes the site as one of the farm’s most extreme bridge crossings in terms of length and height. “I don’t think you’d survive if there was an engineering failure.”
The resulting Tukemokihi bridge is a phenomenal piece of ingenuity which pushed Bridge It NZ’s team to the absolute limit.
In order to install a 50m x 3.6m upright steel truss bridge with timber deck, the bridge had to be designed and manufactured in small modular components (5 x 10m sections weighing five tonne each), so everything was light enough to be transported and lifted onto site using a 30 tonne excavator.
Kiwi ingenuity really came to the fore, and a humble tractor played a key role in both transport and bridge installation. The access roads were too windy for a normal truck and trailer to navigate, but a tractor could go off-road and therefore take wider turns.
A unique launch method had to be developed to literally pull the bridge 50m in mid-air from one side of the riverbank across to the other – something we had never done before – which required us to really think outside the box.
We built a 28m-long temporary launch frame which was attached to the rear of the new permanent bridge, and a central 9m-tall steel tower structure with forward and rear stays to support the bridge during the launch. Bulk bags of soil (weighing a total of 23.5 tonnes) were progressively lifted onto the end of the temporary works to act as counterweight and balance the bridge as it was launched across on custom-made rollers. A series of pulleys were used to gain mechanical advantage and reduce the required pull force to less than three tonne, allowing a small five tonne tractor to haul the entire bridge across the 50m ravine using 13mm dyneema rope.
The end result is nothing short of spectacular.
While the launch was incredibly successful, touching down precisely on the opposite river bank in just one day, this project was not without substantial challenges.
Due to significant consent delays, the project ran through the cold winter months, forcing our site crew to use winches on their ATVs to haul themselves up slippery access tracks – or in some instances, even walk 40 minutes each way – to reach the work site each day.
Bridge It NZ staff had to camp out in the farm’s shearers’ quarters for weeks at a time, forgoing home comforts to get the job done.
This project truly speaks to our company values of honesty, reliability, adaptability, one team, and sense of urgency. With clear communication and exceptional preparation, our staff excelled in the toughest of circumstances.
Tukemokihi Station Farm Manager, Dave Scragg, is very happy with the end result, despite the winter weather delays.
“It’s a credit to them for sticking with the job through the winter and carrying on and getting it finished. It would have been easy to pack up and leave and come back in the summer. So that’s a credit to them in that respect.”
He says the Bridge IT NZ were good to communicate with and regularly kept in touch to work in alongside daily farm operations. “The new bridge is an asset to us. It was a hard three years without a bridge. It’s definitely sped up the flow of stock for that end of the farm and we can take a tractor over it now, which will be helpful.”
Hilton adds that while the project took longer than anticipated, he appreciated how easy it was to discuss problems that arose with the Bridge It NZ team. “I’ve seen over the years some contractors who, when you disagree, they’re happy to walk away from what they’ve already contracted. There was a level of professionalism at Bridge It NZ that you don’t always see. They were pretty good buggers to deal with.”
Overall, Tukemokihi bridge stands as a testament to our team’s resilience and passion for delivering world-class infrastructure. It’s a perfect example of what can be achieved when you combine hard work, innovation, and a shared vision.
If you need help accessing a remote part of your property, give us a call today.
