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

SH1 Mangamuka Gorge slip repairs – October Update

Kia ora koutou,

We have had an amazing month with more settled weather over the last couple of weeks meaning we have been able to maintain momentum and make significant progress.

We have achieved 2 significant milestones over the last 3 weeks with the piling on A5 and A12 being completed. We still have to complete the installation of the lagging walls, capping beams, and ground anchors, but the completion of the piling means that the most technical part of the repairs is now complete for these slips. The large piling drills and cranes used to install the piles can now be moved to the next site. 

With the Spring weather, ground conditions continue to stabilise. However, we are remaining 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 making sure we are prepared with the management of hot works and minimising the risks of fires caused by the activities onsite. 

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.

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

Commitment to the environment recognised

We are delighted to share that our commitment to environmental excellence has been recognised with the project being a finalist at this year’s IECA Australasia Environmental Excellence Awards.

Managing the effects on the environment and to wildlife around the site works are critical to the project team and our partners as the Maungataniwha Ranges are home to a diverse range of native and endangered flora and fauna.

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, says: “This nomination recognises the creative thinking, and efforts being undertaken to find effective and practical solutions to protect the surrounding whenua.”

The winners will be announced at the IECA Australasia and Stormwater Queensland Conference dinner on 2 November 2023.

News and Media

If you missed it last month, check out the link below to see a flyover from early August. We will have another flyover out to you by the end of the year.

Mangamuka Gorge slip repairs flyover: August 2023

Upcoming Events

Keep an eye out on our social media channels over the next couple of weeks for our upcoming engagement pop ups in Kaitaia on the 28th of October and Mangamuka on the 11th of November.

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.

Waka Kotahi NZ Transport Agency – Northland Facebook page

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.

A third large piling rig arrived on site this week, meaning that we are now able to complete the larger permanent piles on 3 sites at a time.

Progress Update

The permanent works are underway throughout the Mangamuka Gorge.

The crews are operating in a challenging environment due to the complex geology of the Maungataniwha ranges and the constrained environment, with large and heavy machinery required onsite to complete the repairs.

This month saw a third large piling rig arrive to site, which means we now have the capability to install the larger 1080mm permanent piles on 3 sites.

Physical works are being undertaken on 8 of the 15 critical slip sites. The remaining sites are currently still being investigated and appropriate designs are being developed.

Slips A1 and A2: Casing installation is complete. Completion of the piling is scheduled for after several more critical slips have been completed.

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, it is logical to complete these operations as the last step when moving back down and exiting the site with the big rig and crane.

Slip A3: Permanent pile casings have been spliced and are being installed.

Slip A3

Permanent works are well underway with spliced casings being drilled to initial depth of 11m.

Splicing of casings in piling operations refers to the process of joining together 2 or more sections of cylindrical casing that forms the external sleeve of the pile.

The casings for this particular slip have now been drilled to the designed depth.

Slip A5: Piling and lagging plates have been installed. The capping beam is now being installed.

Slip A5

With the completion of the permanent pile installation, the team has now transitioned to the following tasks: completing the excavating, removing the work platform and the groundwork to make way for the installation of lagging plates, as well as installing the suspended soffit and initiating the welding of formworks in preparation for the permanent capping beam installation.

Slip A6: Enabling and drainage works are continuing.

Slip A6

We are continuing with the enabling works, which includes installing the enabling piles consisting of a series of 800mm diameter piles, encompassing both reinforced (hard) and non-reinforced (soft) piles. 72 out of the 74 soft piles are complete and 52 out of the 70 hard piles have been completed.

In addition, the teams have installed 2 slot drain pads, addressed rock spalls, completed drainage installations, and established enabling work platforms.

Permanent works are scheduled to begin in mid-November.

Slip A9: Permanent works have commenced with casings currently being installed.

Slip A9

We have completed the enabling works and commenced the permanent piling. Due to the length of the road section, the slip has been divided into 3 sections.

The top sections’ initial 6m casings are installed with splicing to commence in late October. Once spliced these will then be drilled to 11m depths.

The lower section, like the top section, has had initial 6m casings installed. Splicing has commenced and are being drilled to an initial design depth of 11m.

Initial 6m casings for the middle section have been delivered to site and are installed.

Slip A12: Concrete pouring for the permanent piles is complete and work will continue on to A13.

Slips A12 and A13*

Installation of the 38 x 1050mm diameter permanent piles on A12 are now complete.

Simultaneously, teams are continuing with installing capping beam sections on A12, which involves building the retaining wall behind the piles.

On A13, handrails and work platforms are complete and the casings for the permanent piles are arriving to site to be installed.

*Slips A12 and A13 represent complex slip combinations, and the installation of the capping beam and anchors for A12 is currently suspended. To prevent any conflicts, a new slip named A27, (caused by the April 2023 weather event) will be repaired first. A27 will be constructed with precast panels, similar to what was built for the earlier 2020 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