Mairangi Bay Block Retaining Wall Replacement

Project Goal

Our primary goal was to address a deteriorating block retaining wall that had become a significant safety and drainage concern for the homeowner. The old, leaning structure required a complete replacement to secure the property, prevent further water issues, and restore the landscape’s integrity with a robust, long-lasting solution.

Project Challenges

We overcame two key challenges on this site:

• Persistent Wet Weather: The entire excavation phase was hampered by persistent rain, leading to saturated ground conditions. This increased the risk of slumping and made site access and trenching difficult.
• Critical Underground Services: The new wall’s path was directly over a main council sewer line, requiring a specialised construction approach to avoid damaging the pipe.

Our Solution & Process

Our process began with a proactive approach to the challenging weather. By adjusting schedules around the forecast, using tarps, and deploying water pumps, we effectively managed the saturated site to ensure a stable foundation. We then systematically demolished the failed structure and excavated for a new, engineered concrete footing. The new wall was constructed with steel-reinforced, concrete-filled masonry blocks, creating a structurally superior barrier. This methodical process not only restored stability but also vastly improved the property’s drainage and overall aesthetic.

Points of Interest

A key technical aspect of this project involved building directly over a council sewer main. To protect this critical infrastructure, we engineered a solution involving two deep, reinforced concrete piles designed to support the new wall’s weight and transfer the load away from the pipe below. This required full approval from Watercare, and to ensure no impact, we coordinated CCTV inspections of the sewer line both before construction began and after the project was completed.