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

SH1 Mangamuka Gorge slip repairs – September Update

Kia ora koutou,

We have had an amazing month with drier weather meaning we have been able to maintain momentum and make significant progress.

The settled weather of the last couple of weeks has meant that we have seen some major progress. Most of the enabling works are now complete and permanent works are now underway on multiple slip sites throughout the gorge. Next month will see an achievement with the completion of the permanent piles on A5.

Even with the enabling works in place, we are still seeing some ground movement. There are measures in place to keep everyone safe and at times we have needed to stop work when conditions become unsafe, or the numerous sensors positioned through the gorge have indicated ground movement. Read more on these measures in this month’s update below.

As indicated last month, we expect the road to re-open in late 2024.

We appreciate your continued understanding, patience, and support.

Slip A12/A13 permanent piles. The piling rig and crane are in place and underway with the permanent works on A12.

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.

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: Piling sleeves installation is now complete.

Slips A1 and A2

Permanent works are continuing with 40x 6m pile casings installed in preparation for the return of the main piling rig from Slip A5. Once in place, the piling rig will use the casing as a guide to drill down to solid rock. It will then be filled with re-enforced concrete which forms the pile.

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

Slip A3

Permanent works are underway with pile casings are currently being spliced. Splicing of casings in piling operations refers to the process of joining together two or more sections of cylindrical casing that forms the external sleeve of the pile.

Slip A5: Permanent piling is nearing completion.

Slip A5

Teams on site are onto the permanent piling and are finishing the installation of 25x 1050mm diameter piles. This is scheduled for completion at the end of this month.

Slip A6: Enabling and drainage works are underway.

Slip A6

We are continuing the enabling works, installing the enabling piles which consist of a series of 800mm diameter piles, encompassing both reinforced (hard) and non-reinforced (soft) piles. This proactive approach aims to ensure that, once heavy machinery are established on the slip, the ground remains sufficiently stable and any potential for further movement is minimised.

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

Permanent works are scheduled to begin in late October.

Slip A9: Enabling works and environmental control reinstatement is nearing completion.

Slip A9

The team is nearing completion of the enabling works with the capping beam complete and stormwater management controls being re-installed.

Permanent works are scheduled to begin in late September.

Slip A12: Concrete for the permanent piling for 12 is progressing well.

Slips A12 and A13

Teams are continuing with lagging, which is building the retaining wall behind the piles, as well as work platforms in preparation for the staged mobilisation across Slips A12 and A13.

Installation of 39x 1050mm diameter piles on A12 are underway and are progressing on schedule. Due to the access requirements and overall fragility of this section, work will proceed onto A13 once the work on A12 is complete.

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

Stormwater Management

As part of our environmental controls we are continuing to take steps to ensure that wildlife and the land that they are on around the works sites are protected.

As part of this commitment, we are utilising innovative and effective ideas around managing water runoff to prevent contaminants from flowing off the worksite onto the whenua and awa below. 

Water runoff is diverted into a series of clean industrial bins where dirt and other contaminants are allowed to settle, before overflowing into another bin. The remaining contaminants are also able to settle before being pumped out and removed offsite for further settlement and safe disposal.

Examples of the TARP controls that are constantly monitoring ground movement to keep our teams safe.

Safety Around a Moving Whenua

While we have been onsite, we have continued to experience ongoing weather events and a year's worth of rain in under 6 months. The wet weather has meant that at times it has been unsafe to be onsite, with several new slips occurring during this period.

We have a complex network of sensors onsite that are working non-stop to keep the construction site safe. These gadgets are constantly checking ground movement, helping geotechnical engineers know what's happening, keeping the teams on site safe as they do the hard mahi fixing the slips.

The sensors monitor ground movement, check how wet the soil is, and measure how much rain has fallen. Every day, these sensors send data to a special plan that figures out how risky the ground movement is. This plan is called a Trigger Action Response Plan, or TARP. The TARP level is shown throughout the site with lights placed at slip entry points.

If it rains a lot (50mm or more in a day), or if the ground gets wet because it's been raining for a long time, the TARP level goes up automatically. If a sensor notices that the ground has moved substantially since the last reading, alarms will go off and the crews are moved away from the site until it is safe to return.

Sending data out from the gorge is tough because there's no cellphone coverage and power is limited. But the sensor system that keeps our teams safe uses advanced wireless technology to make this possible.

These smart sensors do an important job keeping everyone safe on site. They watch the ground and tell the engineers and workers if anything's not right, even if it's happening slowly or they can't see it right away.

News and Media

Check out the link below to see a flyover from early August. This shows the scale of the work being undertaken in the gorge and the progress to date.  

Mangamuka Gorge slip repairs flyover: August 2023

Upcoming Events

We’ve unfortunately have had to cancel the last couple of engagements due to weather. But with more settled weather on the horizon, keep an eye out on our social media channels over the next couple of weeks for our upcoming engagement pop ups in Mangamuka and Kaitaia.

These popups 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

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