Pine Valley Road Culvert Repair – MagnumStone™ MSE Wall

Pine Valley Road connects State Highway 1 to rural communities near Silverdale on Auckland’s North Shore. Severe weather events in early 2023 triggered an 18m slip, damaging culverts beneath the road and undermining the slope, damaging a gabion wall and a competitor’s mass block retaining wall.

To reinstate the road and culvert, engineers required a vertical retaining wall solution that could provide maximum width for the new road corridor while ensuring long-term slope stability. The MagnumStone retaining wall system offered the design flexibility, durability, performance, and speed needed to complete the project within a tight timeframe.

DESIGN

The repair involved two MagnumStone MSE retaining walls – a 40m northern wall and a 51m southern wall, constructed on either side of a new 2.5m x 2m box culvert positioned 6m below road level.

Both walls were reinforced with StrataGrid geogrid with a positive connection, delivering 100% grid coverage through the reinforced zone for maximum stability and cost efficiency. Designed for full highway loadings, the StrataGrid tiebacks used were between 4m and 6m, including one layer spanning the full 13.5m road width to physically link the two walls and enhance global stability.

To meet project requirements, Cirtex custom-manufactured vertical MagnumStone blocks with a zero-degree offset, deviating from the standard 87.6° batter. This precision manufacturing allowed the walls to meet engineering and aesthetic criteria while maintaining structural performance.

INSTALLATION

After removing the failed materials and old culvert, Downer constructed the new walls around the replacement culvert. Despite limited access and a compressed timeline, Cirtex rapidly scaled production and delivery to maintain a steady supply of custom MagnumStone units, keeping the project on schedule.

Contractors reported that MagnumStone was quick and easy to install, requiring only standard machinery thanks to its lightweight, hollow-core design. Integrated subsoil drainage and riprap protection prevent future scour and erosion. The road was successfully reopened before the holiday period, restoring a vital connection for the local community.

The MagnumStone system provided the following benefits to the project:

• Custom-engineered MagnumStone blocks manufactured for vertical wall design
• StrataGrid positive connection delivers 100% coverage and superior wall performance
• Fast production and delivery turnaround to meet tight construction schedules
• Lightweight, hollow-core design enables quick installation with standard machinery
• Proven MSE wall solution for complex geotechnical and hydraulic environments