The biggest rig currently on site, the Liebherr LB24 Drill Rig, being moved to slip A6 after completing slip A3.

SH1 Mangamuka Gorge slip repairs – March 2024 update

Kia ora koutou,

March has been another month of significant progress, helped by the dry weather. 

This month we’ve completed another slip site, A27, and the final piles have been drilled on 3 more slips, A3, A12 and A13.

The project team is working around the clock to complete as much as they can before winter. This includes reviewing our wet weather plans, ensuring stormwater drains are clear and sediment controls are working properly. 

Just a note that in our last newsletter, we mistakenly shared the before photo of slip A13 instead of slip A12, which is 50m away from slip A13. We’re sorry about that confusion!

Slip A12 – Before and after. The photo on the left was taken March 2023, and the photo on the right was taken in February 2024. Piling and capping beam are complete.

Slip A13 – Before and after. The photo on the left was taken March 2023, and the photo on the right was taken in February 2024. Piling is complete.

12 Months of Progress

Now we’ve had just over a year onsite, we’re excited to share some of the records and achievements from our work in the gorge.

Procurement

• Site hours: 279,994
• Site staff inducted: 734
• Daily average on-site workforce: 142
• % Average local workforce on site: 74%
• Average companies on-site daily: 17
• Companies on-site employing locally: 14 (82%)
• Total number companies involved: 141 (55% Far North Employers)

Site facts

• Total number of slips: 35
• Number of critical slips: 15
• Total number of scheduled piles: 1308
• Enabling works piles: 747x 600mm combined hard and soft piles
• Scheduled permanent piles: 329x 1080mm reinforced bored concrete piles; 72x 600mm continuous flight auger (CFA) piles; 160x Universal Column (UC) retaining wall piles
• Average pile depth (1080mm piles only): 23m
• Deepest pile to date: 32m

Rain, rain, and more rain

Weather has remained a constant challenge with work needing to shut down on several occasions. The last year has remained one of the wettest on record with over 1 metre more rainfall than the historical average in the area.

• Historical annual average rainfall: 1712mm
• Total rainfall: 2801mm
• Peak (mm/hr): 72mm
• Wettest day: 23 September 2023 - 118.8mm
• Wettest month: May 2023 - 542mm
• Driest month: February 2024 - 34mm

Mangamuka Gorge Slip Repairs Wins Site Safe Award

This month our TARP (Trigger Action Response Plan) Sensor system won the 2024 Site Safe Health, Safety, and Wellbeing Awards in the Safety Innovation Award (large organisations) category.

The TARP sensors protect the site teams from the risk of further slips by detecting ground movement and monitoring soil moisture and rainfall levels.

The win recognises the innovative thinking and technology that has been put into place, making sure that the teams up in the gorge stay safe.

For more information on the TARP sensors and what they do, check out our article in the September 2023 update here.

Upcoming Events

Keep an eye out on our social media channels over the next couple of weeks for details of an upcoming engagement pop-up at the Kaitāia Markets in April.

These pop-ups are an opportunity to meet members of the team working in the gorge.

NZTA Northland Facebook page

Slip A26 – UC Column piles being drilled.

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 – Anchors being installed.

Slip A3

Enabling works – complete.

Rehabilitation works – 40/40 permanent piles complete.

The remaining section of the capping beam on the slip has been poured. The grouting team are now on the final stage of the repair to install the anchors.

Slip A4 – Pile locations marked out for coring and casing install.

Slip A4

Enabling works – complete.

The team have continued up the hill from A3 and are now fully underway on A4.

Starting at the southern end, the nightshift team is working on coring and placing casings on the southern end of the slip, while the dayshift team has finished installing the permanent works platforms at the northern end. These are used to provide a stable and level work base for the drill rigs.

Slip A5 – Complete.

Slip A5

This slip is now complete! All piling, lagging, capping beam, and anchors have been installed. The team is now disestablishing the site and moving onto other sites.

Slip A6 – All casings have been installed and piling has begun.

Slip A6

Enabling works – complete.

Rehabilitation works – 13/52 permanent piles complete.

We are continuing to run night and day shifts on A6.

All spliced casings have been installed. We have moved onto installing the permanent piles, with the night shift team drilling the piles to depth and the day shift team handling the reinforcing cage placement, tremmie pipe installation and concrete pours.

Slip A7 – Site preparation for the installation of the UC piles.

Slips A7 and A8

The designs have been finalised. 

While they are both deemed critical slips, they are easier repairs compared to the rest of the slip sites and won’t require the 1m diameter piles.

Minor site preparation has been undertaken on A7 with the main works programmed once slip A26 is complete.

Slip A9 – The bentonite plant has been set up at the northern yard to help stabilise the A9 piles.

Slip A9

Enabling works – complete.

Rehabilitation works – 36/53 permanent piles complete.

The unstable ground at this site has created extra challenges during drilling. As a result, a special type of clay mix called bentonite is being used in the drilling process to help stabilise the pile walls until the reinforcing cage and concrete has been poured.

Bentonite works by suspending the particles being drilled to strengthen and stabilise them. It helps stop water getting into a drilled pile by forming a filter on the side of the hole. The product is reusable so once it's been used, it can be taken out, treated and reused.

Slip A26 – Universal Column (UC) installed and waiting for concrete.

Slip A26

Enabling works – complete.

Rehabilitation works – 9/72 piles complete.

Permanent work has started following the completion of slip A27 with a similar design using universal column piles and precast walls slotted in between.

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 slips A7 and A8, this will be undertaken later in the year around the completion of the other slips.

Slip A11 – Safety barriers in place around the work area to the right.

Slip A11

Enabling works are well underway on the road corridor.

With the environmental permits now in place, work is underway to carefully remove the wildlife and vegetation around the works site before excavation can start. This is being done alongside hapū and our environmental team. 

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 – the capping beam is now complete.

Slip A12

Enabling works – complete.

Rehabilitation works – 38/38 permanent piles complete.

Piling has been completed, with 38 permanent piles, lagging plates, and capping beam now installed.

A second specialist drill rig, like what is on A3, is arriving soon to install the anchors. This will need to be managed carefully because the anchors need to be installed between the piles already installed on slip A27, which is close by.

Slip A13

Enabling works – complete.

Rehabilitation works – 43/43 permanent piles complete.

Piling has been completed, with 43 permanent piles and lagging plates now installed. The capping beam is currently being poured with anchors to follow after A12.

Slip A27 – All piling and precast installation are complete.

Slip A27

Complete!

Worker of the Month

Introducing Wahine toa Tina Mackay, Health and Safety Manager for the Mangamuka Gorge Slip Repairs Project.

Tina's career spans over four decades in the construction industry. She worked primarily as a dedicated truck driver and operator, before moving into her current role of ensuring the health and safety of everyone in a large and dynamic worksite.

She literally helped write the book on piling in New Zealand. Early in her health and safety role, Tina recognised a significant gap in the training and competency standards within the specialised field of piling. Determined to address this issue, she took the initiative to establish a comprehensive training program, which has since evolved into an established NZQA standard in the industry, providing aspiring professionals with the necessary tools and knowledge to excel in the specialised field of piling.

When not donning the Hi-Viz, Tina cherishes moments with her four sons and adored grandson. Tina finds joy in engaging in outdoor pursuits like hunting and fishing, savouring the tranquillity of nature, and cheering fervently for her favourite sport, rugby league.

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