Saving New Zealand’s Matakana Valley Road with a Redi-Rock Hybrid Retaining Wall
Project Name: Matakana Valley Road Slip Repair Owner: Auckland Transport Contractor: Downer Engineer: ENGEO NZ & AU Manufacturer: Duracrete Location: Matakana, North Auckland, NZ Wall Type: Hybrid Texture: Ledgestone Year Built: 2025
THE CHALLENGE
A portion of Matakana Valley Road in rural North Auckland, New Zealand, was simply washing away. January 2023 floods exposed the rural road network to heavy stormwater damage and landslides. The road’s stormwater controls were outdated and poorly constructed, leaving it at risk of collapse and cutting off rural communities from other vital main roads.
To address the slip’s rapidly declining state, the project’s geotechnical, geology, environmental science, and hydrology firm, ENGEO NZ & AU, had to design a solution that would:
- Modify the stream channel to better prepare for future flood events and address the risk of the waterfall overtopping
- Incorporate an anchored headwall design into a retaining wall master plan
- Replace the failing culvert with a new box culvert designed to withstand heavy flood waters, and connectable to a retaining wall design
Whilst dealing with active flooding and the ever-present threat of collapse, ENGEO had to design a retaining wall within an extremely tight footprint, a feat made possible by partnering with Redi-Rock to deliver a long-lasting retaining wall.
THE SOLUTION
ENGEO NZ & AU was first introduced to Redi-Rock through a presentation given by David Hepburn of Redi-Rock’s New Zealand producer, Duracrete. When Auckland Transport engaged Downer as the Matakana Valley Road’s project manager and installer, ENGEO was brought into the picture, tasked with accommodating the site’s challenges into the master retaining wall plan, and they knew just which large-block solution would fit the project’s needs–a Redi-Rock hybrid gravity and mechanically stabilized earth (MSE) retaining wall system.
THE DESIGN
The final retaining wall plan consisted of 28 in (710 mm) Redi-Rock blocks on the top courses and 41 in (1041 mm) on the bottom courses. To abut the culvert headwall, Freestanding Hollow-Core Blocks were used.
Nick Mellsop, Senior Engineer at ENGEO NZ & AU, used Redi-Rock engineering and design tools to assist with the wall plan.
“The design process was made easier by Redi-Rock’s dedicated design software, which is built into GEO5 - a system widely used within the geotechnical industry.” -Nick Mellsop, Senior Engineer, ENGEO NZ & AU
Of the engineering and design resources offered by Redi-Rock, Nick and the ENGEO team utilized:
- CAD files for the blocks
- Corner and curve construction details
- Geogrid testing reports
- RRWall+ design software
“We downloaded CAD files for the blocks, and all the information we needed, especially for geogrid strengths and block layouts for corners and curves.” -Nick Mellsop, Senior Engineer, ENGEO NZ & AU
With a wealth of resources right at his fingertips, Nick and his team propelled the Matakana Valley Road project from the design phase and into installation.
THE INSTALLATION
Construction was completed over six months, from January to July 2025. Downer managed the installation, while ENGEO and Duracrete provided engineering and retaining wall support.
Because a hybrid wall was selected, one lane of Matakana Valley Road could remain open while the wall was built. This also made it easier for installation crews to manage active flooding and stream flow with additional space for temporary construction measures. A traditional MSE wall design would have meant a full road closure, making the already tight construction limits even more difficult to maneuver.
Bringing Duracrete’s delivery trucks onto the site was initially a challenge, but was remedied with Redi-Rock’s machine-set installation capability. A crane was used to lift and place blocks from delivery trucks in staging areas and again during installation. Smaller, hand-set block systems would have been potentially dangerous for installation crews to handle at this challenging site and would have taken much longer to install.
THE OUTCOME
Complete and thriving, the 3,336 sq ft (310 sq m) Ledgestone textured retaining wall system provides improved resilience against stormwater flow and landslides. The choice to bring Redi-Rock into the project remedied the site's previously failing infrastructure and ensured long-term performance for a crucial rural road network. Auckland Transport, Downer, ENGEO NZ & AU, and Duracrete formed a partnership that produced impressive retention outcomes–a project that now stands as a testament to the strengths of teamwork and durable precast solutions.
“It was really easy to work with the Duracrete team. They are very responsive.” -Nick Mellsop, Senior Engineer, ENGEO NZ & AU
Duracrete’s David Hepburn shared his satisfaction with the project via this LinkedIn post: “We are so grateful to ENGEO NZ & AU for selecting Redi-Rock systems as solutions for Auckland Transport at Matakana and for featuring the case study.” In a second post about the project, David also notes, “This slip repair project at Matakana is impressive.” And thanks to Redi-Rock and the entire Matakana Valley Road project team, it is built to stay that way for generations.
Duracrete specializes in turning potentially catastrophic sites into fortified strongholds with their Redi-Rock solutions. View more of their Redi-Rock New Zealand projects: