SH1 Brynderwyn Hills recovery and enabling works

27 May 2024

Approximately 35,000 cubic metres of earth has already been excavated from Kauri Tree Corner (images taken 10 May and 27 May)

What's been happening this week

There has been a lot of interest in how we are clearing the earth that came down in the slips. We mentioned in last week’s newsletter that excavators are working from a platform at the top of the ridge to remove soil, helping to reduce the likelihood of further slips. You can see in the photos above how the cut at zone F has progressed from 10 May compared with an image taken today, 27 May. 

The diagram below is a good illustration of the approach we are taking; it shows a cross section of the hillside at zone F. The shaded area shows the dirt we have cut off the top of the hill to a depth of around 8 metres, with approximately 35,000 cubic metres cut away already. All this dirt has been carted off the hill by more than 2,000 dump truck runs and relocated to a fill site.

The green line shows the hill before the slips occurred and the dotted line shows how it has moved following the slips. We expect to cut back the hillside to approximately the solid black line. The total excavation amount is estimated to be around an additional 55,000 cubic metres removed, once the work at zone F is complete.

View of zone F looking south

The first image was taken 10 May and the second image taken today, 27 May. In the second image you can see the approximately 35,000 cubic metres taken from the top of the slip site so far. 

How drainage is managed

Drainage is a key part of making sure we protect this route for the short to medium term, in the next severe weather event. We are constructing a drainage system along a sloped area beside the road including manholes anchored to the road bank so we can have access to do regular maintenance. A type of pipe called a flume, channels water downhill away from the manholes. This setup prevents erosion of the road by directing water away from the slope, ensuring the road stays safe and stable. The majority of drainage works are safe to carry out at night so can be done 24/7.

Your questions answered

We love that people are engaging with our social media posts and asking questions about the project. Here are some of the most popular questions:

Is work happening 24/7 on the slip?

Excavation work is happening 7 days a week, as long as weather allows. Floodlights are being used in other areas within the closure to complete drainage, soil nailing and pavement works. For visibility and safety reasons, large scale earthworks need to be completed in daylight hours. We are maximising the amount of equipment and crews at each site to complete the work as quickly as possible.

Will the road be safe when it reopens?

The slip at Kauri Tree Corner happened before work to stabilise zone F was complete.  Before the road can reopen at the end of June there will be checks and assessments done to ensure the road is safe.

The work done within the closure such as benching, drainage and retaining walls will all help the road to be more resilient to severe weather. The likelihood of an overslip is greatly reduced with soil nailing, mesh and benching (levels cut into the hillside) which all contribute to a more stable hillside compared with the condition it was in pre-closure.  The newly created shoulder will also give us space to clear any slips with less disruption to traffic, in the event it does occur.

The slip at Kauri Tree Corner was contributed to by an unusually dry soil composition rather than a large amount of rain. This soil composition is not found elsewhere in the closure, so this type of slip will not occur elsewhere in the corridor.

What’s the longer-term solution for this corridor?

After the weather events of 2023, SH1 Brynderwyn Hills remained vulnerable to the next severe weather event and was at risk of lengthy unpredictable closures after big storms.  The recovery work being completed now will ensure this route is reliable for the short to medium term while we progress on a long-term alternative for the Brynderwyn Hills.

Earlier this year Hon Simeon Brown announced an alternative to SH1 Brynderwyn Hills in the draft Government Policy Statement (GPS) on Land Transport. It was one of 15 roads identified as Roads of National Significance (RoNS). NZTA has now released our proposed delivery approach for the government’s 15 RoNS, including the Northland corridor as a priority, in the State Highway Investment Proposal (SHIP). You can read this document here. 

Minister Brown has confirmed that boosting economic growth and productivity is a key part of the government’s plan to rebuild the economy and it’s critical that we move at pace on the Roads of National Significance, getting people and freight where they need to go quickly and safely. The GPS will be confirmed by the Minister later in the year.  

We are moving at pace to position ourselves for successful delivery of the Roads of National Significance (pending funding confirmation under the 2024-27 NLTP).

Specialist Equipment- slipform machine

This piece of equipment makes quick work of installing channels for drainage. Slip forming is the process of laying concrete kerbing using this special machine which pours out the concrete and creates the kerb onsite.

Update on B6

We have been able to make the most of the closure to repair a complex underslip (referred to as B6) on the north side of the Brynderwyn Hills, past the scenic lookout area. Since the weather events in 2023, we have needed to close the passing lane to complete these works safely.

The extended closure has allowed us to progress works at B6 so the passing lane next to the site will reopen at the same time as the Brynderwyn Hills closure works finish at the end of June 2024.

The damage in this area was caused by an underslip which is not as visible as an overslip, where debris comes from above and covers the road. Underslips are also more complex and challenging to fix than overslips. The site has been repaired with a piled wall made up of 20 piles in total, at a depth of 20 metres. A rig drills holes for the piles, then places a metal casing in the hole and reinforcing steel rods inside the casing.

Concrete is poured into the casing to form the pile which is finished with a concrete cap and anchors drilled back into the hill for extra stability.

Rebuilding the pavement in April 2024 and works nearly complete, May 2024 (the retaining wall has been capped on the bottom right)

Crews completing nightwork repairs on Paparoa-Oakleigh Rd

Repairs and maintenance on the 3 official detour routes

During the SH1 Brynderwyn Hills closure Northland is open via 3 scenic detours- SH12/SH14, Paparoa Oakleigh Road and Cove Road. We are proactively monitoring these routes to make sure they are safe and as high quality as possible. Part of this monitoring has included emergency repairs as needed. 

Due to the extended closure we now need to do a number of priority pavement repairs on these routes. You will start to see more activity on the detours as our crews complete these necessary works. Other service providers will carry out works on the road too, such as urgent powerline repairs and maintenance. Please have patience with our crews as they complete these important jobs. We will make sure any delays to journey times are minimised as much as we can, scheduling these at night or at weekends when possible. 

Before you travel, visit our journey planner website to help plan your route and look out for our mobile VMS (variable message signs) which can help you select the best route based on real time data. Further information on routes can be found at the bottom of this newsletter.

Slip known as A6, one of the 15 critical sites in the Mangamuka Gorge

SH1 Mangamuka Gorge slip repairs project- what's happening further north

As well as the Brynderwyn Hills works, we also have crews working hard on the Mangamuka Gorge recovery work, further north on SH1. 

We’ve had feedback on social media that you’re keen to know how this project is progressing. Work is tracking well getting ready for the expected reopening by Christmas 2024.

The Mangamuka Gorge project also has its own e-newsletter and updates on the NZTA Northland Facebook page. You can sign up for the newsletter here and follow us over on Facebook. 

In these updates you’ll get to see the project progressing in detail and receive updates on the 15 critical slip sites within the gorge. This project is quite different to the Brynderwyn Hills work which had a large amount of earthworks. The majority of the work at Mangamuka Gorge is on the downslopes which are more complex and time consuming to fix and is less visible as it is underground rather than above it.

Key information at a glance

SH1 Brynderwyn Hills closed: planned reopening end of June 2024

Three scenic detour routes available:

• Cove Road route: Turn off at Kaiwaka, use Kaiwaka Mangawhai Road, Garbolino Road, Tara Road, Cove Road, Nova Scotia Drive and connect back to State Highway 1. (Restrictions are in place for trucks with trailers on Cove Road between Mangawhai Heads Road and McLean Road).
• Paparoa Oakleigh Road route: Trucks and trucks with trailers up to 50 tonnes can use this route.
• SH12/SH14 route: HPMV (high productivity motor vehicles) must use this route.

Local routes contact

Whangarei District Council 0800 932 463

Kaipara District Council 0800 727 059

State Highway route contact

NZTA 0800 444 449

More information

For more information on the SH1 Brynderwyn Hills project, contact us at northlandproject@nzta.govt.nz

Visit our website www.nzta.govt.nz/brynderwyn-hills