Mangamuka Gorge slip map that shows the locations of all of the current slips in the Mangamuka Gorge.

SH1 Mangamuka Gorge slip repairs – November update

Kia ora koutou,

We have had another good month with more stable weather, which has allowed us to keep up the momentum and make significant progress.

We are now fully mobilised on 6 of the critical slip sites undertaking permanent works at various stages, including drilling, piling, capping beams, and up-slope retaining walls.

Where logistically possible we are undertaking night works to ensure that we maintain this progress.

Ground conditions continue to stabilise. However, we remain vigilant and prepared for whatever the unpredictable Te Tai Tokerau weather may throw at us. With a potential hot and dry summer ahead, we are now shifting our focus to make sure we are prepared with the management of hot works and minimising the risks of fires caused by the activities onsite. 

We investigated opportunities to provide limited access over the Christmas period to connect communities on either side of the gorge. Unfortunately, that can’t be achieved safely, so work will be continuing onsite over the Christmas period.

We are constantly looking at ways we can safely improve our programme however we are still anticipating the road to re-open in late 2024.

We appreciate your continued understanding, patience, and support.

Upcoming events

Thank you to everyone who came to see us at the Kaitaia and Mangamuka markets over the last month. We appreciate your pātai and feedback and look forward to coming back again in the new year.

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

Keep an eye out on social media for future engagements.

Waka Kotahi NZ Transport Agency – Northland Facebook page

Water runoff is diverted into a series of clean industrial bins.

Mangamuka environmental controls recognised

Last month we shared that the innovative storm water controls for the project was a finalist at this year’s International Erosion Control Association (IECA) Australasian Environmental Excellence Awards.

This month we are ecstatic to announce that the project was recognised with a well-deserved Highly Commended award. Congratulations to the team and everybody involved.

Effective stormwater and sediment management plays a major role in protecting the environment through construction. Silt fencing, rainwater capture drains and sediment tanks have been installed to ensure any stormwater runoff is diverted, collected, with silt and other contaminants allowed to settle before it reaches the local waterways.

Project Manager Hendrik Postma said “We are thrilled that this award recognises the creative thinking of the project team, and efforts being undertaken to find effective and practical solutions to protect the surrounding whenua.”

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.

Slip A3 – permanent piles being poured. Movement around site can be challenging while major tasks like concrete pours are underway.

Progress update

The permanent works are well underway throughout the Mangamuka Gorge.

The teams onsite have ramped up their efforts with the benefit of finer weather and are at times drilling up to 4 piles a day which is quite an achievement.

Over the coming months, we’ll continue with permanent pilling works. Currently we are running up to three shifts day and night on both sides of the gorge. The design team is working in tandem to finalise the remaining designs.

This includes specialist work over the Christmas period in an area which requires complicated access restrictions to the rest of the site. 

Physical works are now underway on 11 of the 15 critical slip sites. The remaining sites are being investigated and appropriate designs developed.

While we have been able to ramp up production, health and safety remains paramount on site. The team have worked over 195,000 combined hours onsite to date with no lost time or notifiable incidents. This reflects the safety focused culture on site of which the team can be extremely proud.

Slips A1 and A2

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

The scheduling for the permanent piling operations at this slip prioritises them as the final tasks among all the critical slips.

Since we have positioned the large rigs further up the site, this will be the last step when moving north and exiting the site with the big rigs and cranes.

Slip A3 – permanent piles being poured. The tremie pipe in the middle is used to pour concrete to the bottom of the pile and push any water at the bottom up to a level where it can be sucked out.

Slip A3

The permanent works are progressing well, despite non-favourable ground conditions.

The night shift is focused on drilling the piles, and the day shift is focused on installing reinforcing cages and pouring concrete.

We have a total of 42 piles slated for installation, and as of now, we have successfully completed 9 of them.

The project is on track, with the efforts of both shifts ensuring steady advancement.

Slip A4

The team are finalising the temporary design and setting up to start the enabling works in December.

Slip A5 – the capping beam is now being installed. PVC pipe has been installed to support the installation of the ground anchors once the capping beam is installed.

Slip A5

The steelwork is now completed, and a specialised capping beam team is on-site to install the shutters (the formwork which the concrete is poured).

The initial segment of the capping beam has been completed with 65m3 of concrete poured and is currently undergoing the curing process.

Progress is steady.

Slip A6 – enabling works are nearing completion with the capping beam being installed

Slip A6

Enabling works are nearing completion.

The team has completed all enabling piles and are now onto the installation of the capping beam that will hold the piles in place.

The first section of the beam is complete with the remainder is expected to be complete by the end of November.

Slips A7 and A8

The design team is in the process of finalising the designs.

Slip A9 – permanent works have commenced with casings being splices and secured

Slip A9

Permanent works are continuing with casings being welded and secured.

Simultaneously, we have commenced the drilling process with 4 of the scheduled 53 permanent piles completed.

Slip A26 – slot drains

Slip A26

Upslope slot drain and drainage improvements are nearing completion.

The design team is in the process of finalising the design.

Slip A10

The project team are working together to confirm a contractor to do test anchors to finalise the design to anchor back the existing gabion wall at this slip site.

Slip A11

The design team is working with the contractor, hapū and DoC to finalise the design for the proposed retreat on this particular slip site.

Slip A12 – capping beam is being installed, and A13 permanent piles are underway

Slips A12 and A13

Piling has been completed on Slip 12 with 39 permanent piles poured and the capping beam now being installed. We are currently installing the steel lagging plates behind the piles to provide the support for the capping beam.

The team is making solid progress on Slip A13, with the installation of the 1050mm diameter permanent piles, with 11 out of a total of 41 piles now poured.

Slip A27 – foundations and Universal Column (UC) beam installation has commenced

Slip A27

The team has just started the permanent works on A27 which is one of the more recent slips from the April 2023 weather event. This slip has the potential to close access from the South. Hence we are bringing this work forward to stabilise this slip area.

A27 is defined as an over-slip rather than an under-slip which feature as the majority of the critical slips in the gorge.

Over-slips are where the ground has moved from above and over the road, compared to under-slips, where the land has moved from underneath the road.

The design approach for A27 is similar to the works undertaken for the 2020 repairs with Universal Column (UC) beams and panels being installed to stabilise this section.

Tackling this slip presents unique challenges as it is located above Slip A12 and needs to be coordinated around access and ensuring underground works, such as the installation of the UC beams and ground anchors, do not clash.

Slip A27 – platforms and Universal Column (UC) beam installation has commenced

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