Mangarino Road Slip and rebuild

The Project

The Mangarino Road project, located in the Waitomo District, involved restoring a rural road impacted by a major landslide that spanned the full road width, resulting in complete closure. Waitomo District Council engaged us to develop a practical earthworks solution that would remove the landslide hazard and reinstate the road for long-term use.

Our role

We were engaged to deliver a robust geotechnical design within a tight timeframe to reopen access for residents. The scale of the landslide created key challenges—ensuring temporary excavation stability, managing significant groundwater, and handling a large volume of earthworks.

Our solution involved constructing an engineered earthfill buttress. This included removing around 6,000m³ of failed material and replacing it with a 15-metre high, 70-metre long buttress built at a 26-degree slope using locally sourced GAP100 limestone. A comprehensive underdrainage system was incorporated to manage groundwater and improve long-term stability.

As the excavation progressed, we adapted the benching design to reduce cut volumes and improve efficiency—providing cost savings to the client. Groundwater springs uncovered during works led to targeted changes in the drainage design to directly intercept and control seepage, reducing future risk during storm events.

The Results

The successful completion of the buttress removed the landslide hazard and reopened the road, improving long-term resilience for this section of the network. This project demonstrates our expertise in complex slope remediation and large-scale earthworks. It reflects the HD style—smart, pragmatic thinking and technical clarity—delivered on time, in close collaboration with the contractor.