As property prices soar and demand for space intensifies, developers are increasingly turning to marginal land such as sloped terrain for new builds a
As property prices soar and demand for space intensifies, developers are increasingly turning to marginal land such as sloped terrain for new builds and relying on retaining walls to stabilise these challenging sites. However, when these structures are poorly designed or improperly constructed they pose serious risks leading to structural failures that are not only costly but potentially catastrophic.
Although no hard and fast statistics are available, anecdotal evidence suggests that far too many retaining walls in South Africa are failing because people are cutting corners. From homeowners to developers the temptation to save money by using the cheapest installer or opting for substandard blocks is putting projects at risk.
In many instances retaining walls are seen as just being garden features instead of engineered structures that need to perform under pressure and if not built correctly, they will fail. In many instances the use of hollow core retaining blocks are the perfect solution, providing the strength and holding power required, while providing ample room for vegetation and beautification where required. Information from Terraforce, the country’s top producers of hollow core retaining blocks, suggests the how to avoid costly mistakes:
1. Don’t hire just any installer
One of the biggest mistakes made is hiring installers with little or no retaining wall experience. While many claim they can do the job few are trained in the specific design and structural requirements of retaining wall construction.
Terraforce recommends using their vetted list of professional installers, available at terraforce.com. “We’ve seen too many failures caused by poor workmanship and inexperience,” they caution.
2. Don’t skip the engineer
The South African National Standards (SANS 10400) do allow walls up to 1 metre high to be built without an engineer’s involvement. But Terraforce advises otherwise especially if the wall carries any load or exceeds a 70º inclination.
Even a short wall can collapse if not designed properly. That’s why we say: when in doubt get an engineer. Load-carrying and steep walls always need professional design input.
3. Don’t buy non-compliant blocks
The integrity of a retaining wall is only as strong as the blocks that make it. Unfortunately, many fly-by-night operators are selling blocks that don’t meet the required specifications.
Terraforce blocks are tested both locally and internationally and are manufactured according to stringent standards, including:
• SANS 207 and SANS 10400
• BS 8006-1 and ASTM D6916-18
• CMA (Concrete Manufacturers Association) guidelines
Their licensed producers undergo ongoing compressive strength testing and maintain tight tolerances for weight and dimension. You can find accredited manufacturers here: https://www.terraforce.com/suppliers-installers/
Lastly, it is important to know that while retaining walls might seem like simple landscaping features they are complex systems that require proper planning, design and execution. Saving money upfront by skimping on professional advice or using cheap products may cost far more in the long run not just in rand terms, but in safety and liability too.
COMMON FAILURE POINTS AND HOW TO AVOID THEM
Wall collapses aren’t random they’re usually the result of one or more of the following:
• Incorrect stability calculations: If the wall isn’t properly engineered, it can overturn or shift due to inadequate bearing capacity.
• Poor drainage: Without drainage behind and above the wall, hydrostatic pressure builds up, leading to bulging, sliding or collapse.
• Overly steep design: Steeper walls require more structural mass and engineered reinforcement – yet many walls are built too upright without accounting for this.
• Excavations at the toe: Weakening the base of the wall – especially during nearby earthworks – can cause immediate instability.
• Substandard workmanship: Uneven placement, insufficient compaction and lack of attention to detail all contribute to failures.
• Saturated backfill: Waterlogged soil behind the wall is heavy and exerts pressure that poorly designed structures simply can’t handle.
