High above Cape Town’s glittering Atlantic seaboard lies Nettleton Road, one of the most sought-after addresses in South Africa. Its sweeping views of Clifton and the Twelve Apostles are matched by some of the country’s most valuable real estate. But beneath this luxury lies a persistent challenge: steep, weathered slopes prone to instability when heavy rains strike.
In July 2020, this risk became reality. A section of embankment below Nettleton Road gave way after prolonged rainfall, dislodging debris and threatening properties. The slope failure was triggered by water infiltration into the slope, which reduced the soil’s strength and caused a portion of the embankment to fail. Authorities immediately cordoned off the area on Kloof Road, located directly below Nettleton Road, thus protecting residents and visitors from potential hazards.
Temporary measures, such as covering exposed soil to reduce further water ingress, and placing barriers, were carried out in 2021 to stabilise the situation. These stopgap measures provided enough time for authorities to appoint specialist consultants and contractors to devise a robust, long-term solution.
A collaborative approach
The design was entrusted to HHO Consulting Engineers, a leading infrastructure engineering company that has been operating for more than 90 years in South Africa.
At the heart of remedial solution was the installation of grouted soil nails to reinforce the slope. The soil nails were drilled deep into the slope, then grouted to bond them securely to more competent underlying material. These soil nails act like reinforcing rods, tying unstable soil back into stable ground and providing restraint to future movement.
Soil nails alone does not address surface erosion. To protect the slope from shallow slips and erosion, a layer of reinforcing mesh was fixed to the surface, followed by a sprayed concrete covering applied to over the surface. This shotcrete skin prevents loose soil from washing away, while also distributing loads to the anchors beneath. Together, anchors, mesh, and shotcrete form a composite system which prevents surface erosion and mitigates against future slope instability.
Franki Africa, South Africa’s leading geotechnical contractors, known for its ability to tackle challenging and complex projects, was appointed to carry out this work.
Overcoming the access challenge
The logistics of working on a steep, confined site was one of the biggest challenges on this project. Conventional drill rigs were too large and heavy to be used safely. To solve this, Franki Africa imported a Comacchio MC 3D drilling rig from Italy. Compact yet powerful, the rig was ideal for operating in elevated environments where access is limited. A unique feature of this drilling rig is that the power generating components are housed in a stand-alone power pack, connected to the drilling unit with hydraulic hoses. This means that the load on a scaffold platform is significantly reduced, as the power pack can remain on ground level. This approach allows for lighter and more efficient temporary works.
A bespoke steel platform, supported on scaffold, was designed and erected, and the drilling rig was then hoisted onto this platform, allowing crews to carry out precise drilling operations directly into the embankment. This was necessary to overcome logistical constraints and allowed work to proceed safely in an environment where conventional solutions would have been impossible.
Backfilling and quality control
The eroded section of the slope needed to be rebuilt with engineered fill that was placed behind a newly build wall, the wall being aligned on a slight offset from the toe of the slope Franki Africa used G7 sand as backfill material, which was imported and placed in layers. The selection of sand enabled compaction by means of vibratory equipment which provided efficiencies in the confined spaces while also elimating safety hazard associated with normal compaction equipment in restricted locations. Each layer was compacted and tested for density, ensuring that the fill achieved the specified strength and stability. Rigorous testing was carried out at every stage, verifying that the embankment rebuild would perform as designed.
This backfilling process was not just about replacing lost material; it was integral to the structural stability of the slope. Proper compaction reduced the risk of settlement, ensured the soil nails would perform as intended, and extended the overall life of the slope.
Tackling drainage
One of the main triggers of the failure was water infiltration. Without improved drainage, even the most advanced structural measures could fail in the future. Recognising this, the designers incorporated new measures to facilitate drainage and surface runoff. Subsurface drains were installed to intercept groundwater, while surface channels were reshaped to safely divert rainwater away from the embankment.
These drainage measures are critical for long-term performance. By lowering water pressures within the soil mass, they help maintain stability, reducing the likelihood of future slope failures during increasingly intense rainfalls seen in the region.
Environmental sensitivity and finishes
Clifton’s dramatic setting demands careful attention to aesthetics. Residents were understandably concerned about the visual impact of the rehabilitated slope. To address this, the designers incorporated natural sandstone cladding on selected sections of the slope. This finish blended the remedial works into the surrounding landscape, reducing visual intrusion and preserving the character of the area.
Dust, noise, and environmental disturbances were also carefully managed throughout construction. Mitigation measures ensured that the works respected both the natural environment and the needs of the local community.
Restoring road and services
The rehabilitation works extended beyond the embankment itself. The slope failure had disrupted utilities and roadside infrastructure. As part of the project’s final phase, affected services were reinstated, and roadside parking bays reconstructed. The parking bays will be resurfaced with new asphalt, returning full functionality to this section of road and restoring convenience for residents and visitors.
Conclusion
From the moment the embankment failed, the story of Kloof Road has been one of rapid response, thoughtful design, and innovative construction. What began as a hazardous collapse has been transformed into a model of slope stabilisation.
With soil nails locking the slope into place, shotcrete skin preventing it from erosion, and drainage controlling the water that triggered the slip, the slopes on this section of Kloof Road now stand secure. Finished with natural stone and new asphalt, the project is a reminder that even in the face of natural challenges, engineering can deliver solutions that are safe, resilient, and respectful of the environment.
For Clifton’s residents and visitors, the project has restored peace of mind. For Cape Town, it offers a blueprint for protecting its hillside roads against the growing threats of climate and terrain. In every sense, the Kloof Road project represents the move from slip to grip.
