Old Howick Road Project – Pietermaritzburg: A Case History
Introduction
In 1994, a significant engineering project was undertaken to address an unstable embankment along the Old Howick Road, situated between Pietermaritzburg and Hilton. This ambitious endeavour involved the innovative use of Class A Galvanised Gabions, designed to provide stability and support to the precarious landscape. This page explores the key aspects of the project, highlighting its design, execution, and enduring success over three decades.
Project Overview
The Old Howick Road project was initiated to combat the challenges posed by an unstable embankment that threatened the safety and accessibility of this vital roadway. To tackle this issue, a robust and effective solution was required. Collaborating with engineers Uhlman Witthaus, Prins and Louis Cheyne played a central role in the engineered design of the gabion wall, which has since proven to be a durable and reliable structure.
Engineering Design
The gabion wall was constructed using Galvanised 2x1x1 boxes, featuring 4-meter-long mesh tails that extended horizontally behind the baskets into carefully selected backfill material. This design not only provided immediate support but also ensured the long-term stability of the embankment.
The hexagonal mesh utilized in the construction was heavily galvanised, featuring a mesh size of 80x100mm and a wire diameter of 2.7mm. The panels of this mesh were strategically extended from the base of the gabion baskets into the fill behind, which significantly reduced the amount of rock infill required within the gabion baskets. This innovative approach not only optimized material usage but also enhanced the structural integrity of the wall.
Project Management and Execution
The project was commissioned by the Pietermaritzburg Municipality, and I had the privilege of managing the installation phase. Louis Cheyne responsibilities included ensuring that the mesh and geotextile were correctly positioned behind the gabion baskets and that the backfill compaction was executed properly. This step was crucial, as improper placement or compaction could lead to movement of the baskets during the filling process, jeopardizing the entire structure.
One of the critical challenges during installation was the use of a large vibratory roller for compaction. It was imperative to maintain a safe distance from the wall to prevent any potential basket settlement and movement, which could have had detrimental effects on the overall stability of the structure.
Long-term Performance and Maintenance
In the years following the installation, Louis Cheyne conducted several follow-up site visits to monitor the performance of the gabion wall. Most recently, in 2024—31 years after the project’s completion— he undertook a comprehensive site investigation. The results were promising, there was no evident corrosion of the basket mesh, no signs of settlement, and the enhanced growth of vegetation covering parts of the wall indicated a healthy integration of the structure with its environment.
Conclusion
The Old Howick Road project stands as a testament to effective engineering and project management. With over 30 years of successful performance, the gabion wall has not only fulfilled its intended purpose of stabilizing the embankment but has also contributed positively to the local landscape. This case history underscores the importance of thoughtful design and diligent implementation in civil engineering projects, demonstrating that with the right approach, structures can withstand the test of time.
