SH1 Mangamuka Gorge slip repairs

Project update

30 September 2024

With the completion of piling on Slip A8, we are now saying goodbye to much of the equipment used for the piling repairs. Here, the last of the smaller drill rigs awaits collection.

SH1 Mangamuka Gorge slip repairs – September 2024 update

Kia ora koutou,

It’s been another bustling month in the gorge as we celebrate reaching 500,000 hours onsite since we began work in February last year.

As our piling crews wrap up, the pavement teams are now fully underway with multiple crews working on reinstating the road. In addition to reinstating the road around the slip sites, the pavement teams are also repairing areas where we have installed new culverts.

Multiple anchor teams are also ramping up production throughout the gorge.

We’re excited to announce the successful completion of Slip A10 this month, and we've also finished piling on Slip A8. This marks the end of piling for all 15 original critical slips. The only remaining piling work is on the slip from the bad weather in June this year, Slip A47, which we expect to complete by mid-October.

We’re on track and excited to reopen the road by Christmas this year.

Thank you for your continued support!

Click on the image above to hear from Pene Subritzky - Traffic Management Department Supervisor, as part of our worker profile series featuring a few of the team working on the project (filmed earlier this year).

Behind-the-scenes project videos

If you missed it last month, check out our behind-the-scenes progress videos. These updates provide a glimpse into various aspects of the project and the people involved.

Voices of Mangamuka Gorge: Pene Subritzky

Voices of Mangamuka Gorge: Brenda Reichardt

Voices of Mangamuka Gorge: Howard Mills

How local workers are shaping the future of Mangamuka Gorge

Rebuilding Mangamuka Gorge: complex engineering for extreme weather

Mangamuka Gorge nightworks

A cross section showing the layers of a typical section of road. The depth of each layer varies throughout the gorge and depends on the location and areas of high wear (such as steeper slopes and corners).

Mangamuka road layers: what lies beneath

With piling nearing completion and the pavement crews now fully mobilised on site, we’d like to provide a brief explanation on what the road (or pavement) is made up of.

There's a lot more below the surface than just the asphalt we drive on. There are several key layers, each playing a crucial role in the road’s overall performance and longevity.

• Wearing/surface course: The top layer is made from asphalt, providing a smooth, durable, and skid-resistant surface for vehicles while protecting the underlying layers from environmental factors such as moisture and temperature fluctuations.
• Base course: Typically made of crushed aggregate or gravel, which further strengthens the road surface by distributing the loads from the layers above.
• Subbase: An aggregate layer which provides additional support and enhances load distribution and drainage.
• Subgrade: The bottom layer, consisting of the natural soil or rock that supports the entire road structure. 

Ensuring each layer is designed and constructed correctly is essential for a long-lasting road structure.

Milling of the old road surface in preparation for new asphalt to be laid between slips A8 and A9.

Progress update

Slip A47

Rehabilitation works: 22/31 permanent piles complete.

Work is underway with the casing and piling on this repair.

The casings are used to hold the shape of the piles while the Universal Columns (or H-piles) are installed, and concrete is poured. These will be cut down and the timber lagging will be installed once the piling has been completed.

Piling is over halfway complete and is expected to be fully complete by mid-October.

The crew installing the casing and H-piles.

Slips A1 and A2

Rehabilitation works: 40/40 permanent piles complete.

The capping beam has been completed and anchor installation is next.

Capping beam is complete.

Slip A3

Rehabilitation works: 40/40 permanent piles complete. 42/42 anchors complete.

The guardrails have been installed. Reinstatement of the road will complete all works on this slip.

Slip A4

Rehabilitation works: 36/36 permanent piles complete. 11/36 anchors complete.

The capping beam is now complete. Anchors are being installed, which is the last stage of this repair.

Anchor installation underway.

Slip A5

Rehabilitation works: 25/25 permanent piles complete. 25/25 anchors complete.

The guardrails have been installed. Reinstatement of the road will complete all works on this slip.

Slip A6

Rehabilitation works: 54/54 permanent piles complete. 17/44 anchors complete. 

The capping beam has been completed and the anchors are being installed, which is the last stage of this repair.

Anchor installation continues. The guardrails have been covered to protect them during drilling.

Slip A7

Rehabilitation works: 54/54 UC (Universal Column) piles complete.

Lagging has been installed, and the teams are currently tidying up and backfilling the site for road reinstatement.

The anchoring system required for this slip is much shorter and quicker to install than the larger piled walls. This will be completed following the reinstatement of the road.

Piling is complete with dig out, and wooden lagging is nearing completion.

Slip A8

Rehabilitation works: 68/68 permanent CFA (Continuous Flight Auger) piles complete.

Piling is now complete and marks the end of the piling work on all 15 original critical slips.

Bore drainage is now being drilled under the southern section to complete the slip repairs, and the pavement teams are now onsite to reinstate the road.

Drilling the final pile

Slip A9

Rehabilitation works: 53/53 permanent piles complete. 42/52 anchors complete.

The team is continuing to make good progress with the installation of the anchors. All of the installed anchors have been stress tested with great results. Stress testing is where the installed anchors are pulled to 150% of their design specifications and checked for any movement. If an anchor shows any movement or fails, it will need to be re-installed.

Anchor installation.

Slip A26

Rehabilitation works: 74/74 permanent UC (Universal Column) piles complete.

The installation of the concrete panels is now complete. Road reinstatement is underway.

The wall is now complete, and road reinstatement is underway.

Slip A10

The drainage, stabilisation of the existing gabion wall, and road reinstatement is complete. The guardrails are now being installed.

Pavement and drainage is complete, and the guardrail is being installed.

Slip A11

This area has experienced movement during the winter months, and our geologists and TARP (Trigger Action Response Plan) sensors are continuing to monitor it closely.

Although we have continued to see movement, excavating and removing material from the hillside has reduced pressure on it and created a buffer zone which helps keep our teams safe. This means any further slips will not fall onto the road.

Road reinstatement is complete, and roadside drainage is being installed that will divert water away from the site and into one of the upgraded stormwater culverts.

The final repairs will be completed after winter to stabilise the slope further including removing any loose material that has the potential to move.

Road reinstatement is complete.

Slip A12

Rehabilitation works: 38/38 permanent piles complete. 37/38 anchors complete.

Guardrails have been installed. The pavement crews are currently installing the sub-grade and base courses as part of the road reinstatement. 

The final anchor will be installed once the road reinstatement is complete, and a smaller anchor rig is available to avoid damaging a large Puriri tree adjacent to the wall. While important to the overall design of the wall, this anchor is not critical to the immediate safety of the wall.

Subbase being installed.

Slip A13

Rehabilitation works: 41/41 permanent piles complete. 28/42 anchors complete.

Guardrails have been installed.

The anchor teams have moved to Slip A6 while the pavement teams complete the reinstatement of the road from slips A12 to A13 in one continuous section.

Once the pavement crews have completed their work, the anchor teams will return to complete the last remaining anchors with added protection to ensure they don't damage the new road surface.

Subgrade being prepped for the road reinstatement.

Slip A27

All work is complete.

Worker of the month

This month, we’re highlighting Bruce Van der Hoek, Kerikeri Branch Manager for Masons Contracting.

With an impressive 23-years at the company, Bruce is a veteran in the industry who has truly done it all. From roading and civil works to drainage and subdivisions, Bruce has worn many hats—starting as an operator, then moving through the ranks as a foreman and supervisor at Masons' main branch in Warkworth. Originally based in Wellsford, Bruce has since relocated north to Kerikeri, closer to Mangamuka, his wife’s hometown.

Bruce's connection to the industry runs deep, having learned the ropes from his father, who also works in the field as a grader operator. This legacy has shaped Bruce’s calm and steady approach, earning him great respect among his colleagues and peers. His years of experience, combined with his hands-on knowledge, allow him to manage the complexities of each project with a level-headedness that is second to none.

When asked about the challenges of his job, Bruce said one of the toughest aspects is ensuring traffic safety. "Keeping the flow of traffic at a safe speed is crucial to making sure everyone gets home safely at the end of the day," he says, giving special praise to the traffic control teams who work alongside him to maintain that safety.

Outside of work, Bruce is an avid outdoorsman. When he's not overseeing projects, you can often find him out on the water, enjoying his favourite pastime—fishing. His love for the outdoors mirrors the hands-on, grounded approach he brings to his work in the civil construction industry.

We’re proud to feature Bruce as this month’s worker of the month

Worker of the month – Bruce Van der Hoek behind the controls of the digger on Slip A12.

Your feedback

Thank you to everyone who contributed to our recent survey about our project communications. Your feedback helps us find out what you find useful and where you’d like more detail. From the feedback we received, we are pleased that most of you are happy with our updates.

With several more months to go before we open, we’ll continue to provide you with regular updates.

You can view the full survey results here: SH1 Mangamuka Gorge communications survey infographic

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