SH1 Mangamuka Gorge slip repairs

Project Update

25 June 2024

Slips A1 and A2 – LB 24 piling rig during night works.

SH1 Mangamuka Gorge Slip Repairs – June 2024 Update

Kia ora koutou,

Despite winter’s arrival with several storms rolling through over the past month, work at the gorge is on track and continues at pace.

Mangamuka Gorge has its own unique challenges due to its geology and varying terrain. As expected, with the heavy rain in the Far North, there has been ground movement on the cut side of our most complex slip repair, A11. See below for some more info on how we are approaching the repair on this slip site.

Unfortunately, during the heavy rainfall on 19 June, a new slip occurred just north of the northern-most slips (A1 and A2). It's approximately 20m long and 3m deep from the edge of the road. Due to the severe weather, no one was working at the time and there were no injuries. Our experts are now assessing the slip to identify the extent of the damage and develop a plan for its repair. Once this has occurred, we can provide further information.

We don't expect this new slip to affect the reopening date, and we’re still on track to be open by Christmas this year.

We appreciate your support and your patience as we work to ensure the safety and efficiency of our ongoing works during the wetter winter months.

Slip A11 - you can see the slip area approximately 20 metres below the road.

Top 3 FAQs about Slip A11

We’ve received some great questions about slip A11 following our recent update, so we are back to answer the 3 most asked questions about our most complex slip:

Why does the A11 repair involve an excavation cut back instead of a piled wall like the other critical slips?

We needed a different approach due to the depth and extent of the slip-prone area discovered following the severe storm in 2022, ongoing monitoring, and ground testing (the photo below shows the slip area about 20 metres below the road). If we repaired this in a similar way to the other critical slips by constructing a piled retaining wall, we would have needed to build a terraced 3-wall system to try and contain the underslip and overslip material. That isn’t cost effective or feasible. Realigning the road away from the slip-prone area is a better long-term solution.

What happens now the excavation works have been completed?

We know that ground can move after it has recently been worked on, especially through the Mangamuka Gorge. We started the cut prior to the wet season so we could carefully monitor ground movement during any rain event. We’ll then schedule the next stage of work depending on how the cut slopes react.

What works are left to do?

If there's significant ground movement we have a few options to stabilise the ground before we build the new section of road, such as rock spall walls, soil nails, or anchors. We’ll also upgrade the drainage to better manage stormwater by diverting it away from the road as effectively as possible. After we've built the new section of road, we’ll use the trees, vegetation, and topsoil carefully removed from the slopes to rehabilitate the old road area.

Hapū and Iwi Partnerships in the Gorge

We have members of mana whenua, hapū and iwi in a range of different roles on the project. These representatives have vital roles on site as part of the day-to-day operations, as well as being involved with engaging and working with other local stakeholders in and around the site and keeping their connected communities up to date.

Nā te iwi me ngā hapū i takohatia he ingoa, he waitohu hoki mo te kaupapa nei – Maunga Taniwha e tū iho nei.

“He mea tapa ki te pae maunga e whītiki ai te huarahi me te tuku mihi hoki hei whakanui i te maunga e tū iho nei.

E rite ana te hua o runga ki te kahiwi o Maunga Taniwha. Kā mutu, ko te rārangi o raro, he mea rite ki te huringa o te rori, mai i te marae o Mangamuka tae noa atū ki te riu o Mangataiore i te raki.

Ko te kara o He Whakaputanga 1835 te tūāpapa e ārahi nei i o tātou mahi ki o tātou hoa Tiriti, pēnei i ā Waka Kotahi.”

Hapū and iwi have also gifted the project a name and logo that we are proud to be able to share – Maunga Taniwha e tū iho nei.

“Maunga Taniwha is the name given for the mountain range that the Mangamuka Gorge passes through and e tū iho nei to ‘stand up’ meaning Maunga Taniwha standing before me.

The top outline of the logo represents the familiar view of the Maunga Taniwha ridgeline, and the bottom line is the route the road follows from Mangamuka Marae to Victoria Valley on the northern side.

The insert represents He Whakaputanga 1835 declaration which is our overarching document which we work under as Treaty Partners alongside with Waka Kotahi.”

News and Media

We were pleased to be able to host media on-site last month to show them our progress.

Check out the links below to see media coverage from this: 

Te Hiku Media: Mangamuka gorge set to open in December 2024

Te Kūkupa: 
https://www.facebook.com/tekukupanews/videos/444617024953677

One News: Mangamuka Gorge to reopen by Christmas after two-year closure

Te Karere: Mangamuka Gorge to reopen by Christmas after two-years closure

Radio NZ: Northland's Mangamuka Gorge to reopen by Christmas after two-year closure

Northern Advocate: State Highway 1 over Mangamuka Gorge in Far North on course to reopen before Christmas

Northern Advocate: Mangamuka Store survives SH1 closure thanks to locals and workers

Progress Update

Slips A1 and A2

Rehabilitation works – 13/36 permanent piles complete.

Permanent piling works have commenced. Running two shifts to keep up the pace, the nightshift team are drilling and the day shift team are prepping and placing the reinforcing cages into the pile and pouring concrete.

Concrete pour underway on one of the piles.

Slip A3

Rehabilitation works – complete!

Slip A4

Rehabilitation works – 20/36 permanent piles complete.

The piling team is maintaining an impressive pace on permanent piling - drilling a pile to the required depth one day, and then installing reinforcing cages and concrete the following. These activities are being run simultaneously, with the team aiming to install 5 piles a week.

Mangamuka rush hour. Space is at a premium with both piling and concrete pouring underway at the same time.

Slip A5

Complete!

Slip A6

Rehabilitation works – permanent piling complete.

The steel work for the capping beam and anchor coring is complete. Pouring concrete for the capping beam is over 50% complete, with the works due to be completed by early July.

Steel and formwork in place in preparation for the capping beam concrete.

Slips A7 and A8

Site preparation is complete, which included cutting the access track downslope for the drill to access under the road. The main works will start at the end of this week.

Slip A9

Rehabilitation works – permanent piles and capping beam complete.

Anchor installation is next for this slip.

The capping beam is now complete.

Slip A26

Rehabilitation works – permanent piles complete.

Crews are now demobilising and moving down to A7. The next stage at this slip involves installing and securing the reinforced concrete panels.

The last of the UC piles have been installed.

Slip A10

Test anchors have been installed and tested. Physical works are scheduled to start in early July.

Slip A11

The initial stage of this repair is complete with close to 28,000 cubic metres cut from the side of the maunga in just over a month. 

More detail around the works here can be found at the top of this newsletter.

Stage 1 cut is now complete.

Slip A12

Enabling works – complete.

Rehabilitation works – permanent piles and capping beam complete.

The anchor drilling team is continuing to install anchors with 2 drill rigs operating simultaneously onsite.

Anchors being installed.

Slip A13

Rehabilitation works – permanent piles and capping beam complete.

Steel works and anchor pockets are complete, and the capping has been poured.

Next will be the anchor installation which is programmed to begin once the neighbouring site A12 has been completed.

The final section of this capping beam being poured.

Slip A27

Complete!

Worker of the Month

We are delighted to introduce Hauraki Kepa as our Worker of the Month.

Hauraki began his career with CLL over three years ago as a Groundsman. His fascination with machinery, particularly cranes, mirrors his father's influence and has profoundly shaped his professional path. Inspired by this passion, Hauraki dedicated himself to learning as much as he could and achieved certifications in slinging and lifting, advancing to his current position as a Dogman within the company.

As a Dogman, Hauraki plays a crucial role on the slip site, performing various tasks and serving as the dedicated spotter for the crane operator. From participating in evaluating the correct chains for the cranes heavy lifts, to setting up the tremie pipe for pours and being on hand to dissemble as the pour proceeds.

Working with large machinery and navigating uneven terrain, safety has been a paramount concern for Hauraki, and he takes that responsibility very seriously. His diligence in this regard underscores his commitment to ensuring a secure working environment.

We eagerly anticipate seeing Hauraki continue to operate machinery and impart his knowledge to the next generation. His dedication and enthusiasm make him an invaluable asset to the project, exemplifying our dedication to excellence in the industry.

Hauraki Kepa working to place the tremie pipes during a concrete pile pour on one of the slips.

Need more information for your local community group?

Our latest flyer ensures you and your community are kept up to date.

If you would like some printed copies to hand out to your whānau or community group, send us an email at northlandproject@nzta.govt.nz with your name, mailing address and the number of copies you need. We’ll then pop them in the post directly to you.

Electronic version of the flyer

For more information about the project, visit the website:
SH1 Mangamuka Gorge slip repairs

More information

For more information on the SH1 Mangamuka Gorge slip repairs, contact us at northlandproject@nzta.govt.nz

Visit our website www.nzta.govt.nz/mangamuka