Slip A12 – 12 months on. The photo on the left was taken in March 2023, and the photo on the right was taken February 2024. Work is nearing completion on this slip.

SH1 Mangamuka Gorge slip repairs – February update

Kia ora koutou,

The end of February 2024 marks one year since we started the physical work in the Mangamuka Gorge. In that time, the team has faced major challenges with one of the wettest winters on record and difficult terrain in tight working conditions.

Despite these challenges, the team have made an incredible amount of progress. This month marks a major milestone - the first slip repair is fully complete.

As the dry summer continues, the project team is working around the clock to get as much work as they can completed before the wetter winter season.

News and Media

Check out the link below to see a flyover from December 2023. You can see the transformation across the site since our last flyover in August 2023, with piling nearing completion on several of the slips.

Mangamuka Gorge slip repairs flyover: December 2023

Upcoming Events

Keep an eye out on our social media channels over the next couple of weeks which will provide details on our upcoming engagement pop-ups at the Mangamuka and Kaitāia Markets in April.

These pop-ups are an opportunity to meet members of the team working in the gorge to talk about what we are doing, from those on the ground doing it.

Waka Kotahi NZ Transport Agency – Northland Facebook page

Slip A6 – Spliced casings for installation. These have all now been fully installed.

Progress Update

Slips A1 and A2

All enabling works and permanent casings for the 1050mm diameter piles are complete.

The programme for the permanent piling operations at this slip is one of the final tasks among all the critical slips.

Since we have positioned the large rigs further up the site, this will be the last slip site to be completed as we exit the site with the big rigs and cranes.

Slip A3 – formwork for the capping beam has been installed.

Slip A3

Enabling works – complete.

Rehabilitation works – 40/40 permanent piles complete.

In the past fortnight, we've reached a significant milestone by successfully finishing all 40 of the 1050mm diameter piles.

With the piling crew now moved onto their next slip, the capping beam team is continuing to install steel and boxing up the completed section of the beam. Approximately 40% of this stage is already complete.

Slip A4 – enabling works are complete.

Slip A4

Enabling works – complete.

Following the completion of slip A3, the crew has moved onto this slip to undertake the final enabling works. This involved addressing tricky-to-access piles and relocating a crossroad culvert. With the culvert relocation now finished, we've successfully completed the additional 12 piles on this slip and poured the remaining section of capping beam.

Slip A5 – anchors being installed.

Slip A5

This slip is now complete! All piling, lagging, capping beam, and anchors have been installed and we are now testing the anchors by stressing each one to test its load bearing capacity and stability.

Slip A6 – splice casings being installed during the night shift.

Slip A6

Enabling works – complete.

We are currently running night and day shifts to complete A6.

During the day shift, workers are engaged in the process of splicing casings, which involves joining together sections of casing that are used during piling to ensure the correct direction of the drilling. 

The night shift then installs the spliced casings by screwing them into place.

Slips A7 and A8

The designs have been finalised. While they are both critical slips, they are a slightly easier repair compared to the rest of the slip sites and won’t need the 1m diameter piles. These have been programmed for the middle of the year around the other repairs.

Slip A9 – completed piles waiting for the capping beam cages to be installed.

Slip A9

Enabling works – complete.

Rehabilitation works – 31/53 permanent piles complete.

To work as efficiently as possible, A9 has been divided into three sections, each with its own set of ongoing tasks.

At the northern end, the pile installation has finished, and steel fixers are currently busy installing the capping beam cages.

At the middle section, the piling crew is engaged in installing piles.

At the southern end, welders are busy splicing casings with the piling crew screwing them into place once spliced.

Slip A26 – Universal Column (UC) beams onsite for installation.

Slip A26

Enabling works – complete.

Works around this site are continuing, but the main permanent works are on hold to allow access for other slip sites that are more established. Work is programmed to start again once slip A27 is complete in early March.

Slip A10

Test anchors have been installed and tested. The design involves installing new anchors to reinforce and tie the existing gabion wall back into the hill. Like A7 and A8, this will be completed later in the year around the completion of the other slips.

Slip A11 – 3D modelling of the area that needs to be cleared.

Slip A11

Enabling works are well underway on the road corridor, which includes the implementation of traffic diversions and the construction of barriers around the work area. Safety ropes and anchors are also being installed to keep crews working on the steep hillside safe during the initial clearing of the site.

Approximately 24,000m3 of material needs to be removed, and the existing road needs to be realigned away from this slip-prone site.

Slip A12 – piling is finished, and the capping beam is nearing completion. Anchors will need to be carefully installed around A27 being built on the opposite side of the road.

Slip A12

Enabling works – complete.

Rehabilitation works – 38/38 permanent piles complete.

Piling has been completed, with 38 permanent piles and lagging plates now installed. The capping beam is expected to be completed by the end of February. Following this the anchors will be installed. This will need to be undertaken carefully as the drilling needs to be done between the H-piles that are already installed on slip A27, which is in the same area.

Slip A13 – permanent piles being installed.

Slip A13

Enabling works – complete.

Rehabilitation works – 38/43 permanent piles complete.

Being arguably the most challenging section to carry out piling so far, the team is using the expression "seeing the light at the end of the tunnel". Work is underway on the final 6 piles.

Slip A27 (right) – platforms, Universal Column (UC) beam and precast wall installation.

Slip A27

Rehabilitation works - 28/32 permanent piles complete.

This site is nearing completion with only 4 Universal Column (UC) beams remaining to be installed. The design of A27 is very similar to the repairs carried out during the 2020 closure.

Worker of the Month

Introducing Ngaire Rihari, our Mangamuka Gorge 'Worker of the Month'.

Ngaire, one of our Vacuum Truck Operators, stands out for her exceptional leadership and commitment to maintaining the highest standards of health and safety on site. Ngaire's guidance and expertise are invaluable to the team, and we would be at a loss without her steady hand at the helm.

Ngaire, a longstanding member of TDG Environmental, played a significant role as part of the original slip repair team during the 2020 closure. With 20 years of experience in the civil construction industry, her passion for driving trucks and operating heavy machinery is matched only by her unwavering dedication to her craft.

On any given day, you'll find Ngaire tirelessly navigating the site, meticulously assessing environmental bins in need of transfer to the refuge station for additional filtering. Her duties extend to pumping water from the awa and diligently washing roads and work sites to clear them of debris and, particularly during the hotter months, for dust suppression. Ngaire's involvement doesn't stop there—she's also on hand during pile pours, managing the removal of slurry and flawed concrete from the surface layer. With her extensive experience in machinery and truck driving, Ngaire plays a pivotal role in ensuring the smooth coordination of on-site traffic control. 

Beyond her professional accomplishments, Ngaire is a loving mother of two, and her profound love for the industry is evident in her daughter's decision to pursue a similar career path. Ngaire's resilience, both at home and on-site, serves as an inspiration to us all, embodying the strength and determination needed to overcome any obstacle.

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.

To view the electronic version of the flyer, click here.

For more information on the project, please click here for the website.

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