GABIONS ARE SCALABLE, FLEXIBLE AND DESIGNED TO BLEND IN

A mainstream choice for civil and environmentally engineered structures worldwide, gabions have stayed the test of time over centuries due to their flexibility and sustainability. Alastair Currie speaks to Louis Cheyne, managing director of Gabion Baskets, about recent projects where his company’s manufactured systems have provided functional and aesthetic solutions.

One of the key roles that gabions perform is earth retention and erosion control due to their characteristic rock-filled wire-frame composition. Combined with the use of geotextile liners, this enables the designer to control the degree of permeability,” explains Cheyne.

“That’s crucial for installations such as mass gravity retaining walls and for riverbank protection where hydraulic factors need to be carefully considered. Here, the approximately 35% voids composition of gabion baskets, mattresses and related systems provides unrivalled performance when designed by experienced environmental engineers with an expert understanding of soil mechanics. With creative thinking, those designs can be shaped into a wide configuration of engineered structures that serve the dual purpose of form and function,” he continues.

Amphitheatre

A recent example is an amphitheatre built for Summerhill Preparatory School, nestled amid pristine riverine forest in the idyllic Hazyview region of Mpumalanga.

Recently, the school encountered a challenge when heavy rainfall triggered a troublesome landslide, affecting the surroundings of some classrooms.

Determined to find a sustainable solution, the school reached out to Fanie Joubert, director of Civil, Structural & Eco-Solutions, and the representative of Gabion Baskets in Mpumalanga and Limpopo.

Entrusted with the task of planning, designing and implementing an environmentally friendly remedy, Joubert conducted a meticulous survey of the affected area, leading to the creation of a oneof-a-kind, open-air amphitheatre classroom. Facing obstacles such as consistent groundwater seepage and highly erodible soil, Joubert installed fin drains to manage the water and successfully designed a layout that perfectly suited the unique characteristics of the area. The final design showcases six spacious platforms, each 3 m wide, with the longest platform stretching 21 m. With convenient walkways on both sides, these platforms provide easy access for everyone.

The benches, crafted using 500 mm x 500 mm gabions, offer a combination of strength and elegance. Then to ensure the safety of the learners and keep unwanted critters away, the exposed vertical sides of the gabions are lined with artificial grass. The finished product is a truly remarkable addition, reflecting the school’s unwavering commitment to providing an exceptional educational environment.

Seaview mass gravity wall

“A key advantage of gabion systems is their scalability and the ability to use a wide range of fill compositions, depending on whether it’s an engineering or landscaped architectural application. For mass gravity applications, another key benefit is that gabion retaining walls tend to occupy a much smaller foundation footprint compared to those constructed with concrete retaining wall systems. This is especially the case as the height of the wall increases. That has major cost and practical benefits in terms of optimising land use,” Cheyne explains.

A recent example is an erosion intervention in the suburb of Seaview, eThekwini, where extensive flood damage resulted in major riverbank erosion, placing a bordering property, as well as neighbouring ones, at risk. As part of its turnkey offering, which includes installation training, Gabion Baskets provided a design recommendation. The proposal was for a 7 m high and 75 m long land-based mass gravity wall, with the client’s

The top of the wall facing the river engineer, LSC Brunette Consulting Engineers, refining the final design based on the findings of the geotechnical report.

“As the normal flow of the river is about 15 m away from the buildings in question, it was decided not to employ a riverbank erosion protection wall and allied gabion mattress foundation setup. The goal was to position the mass gravity wall as close to the building perimeter as possible to mitigate future flood events,” Cheyne continues.

Stormwater channel

Erosion comes in many shapes and forms, and one of the chief causes is uncontrolled stormwater run-off. Here, the installation of gabion mattresses is proven to slow down stormwater velocities in a controlled manner that promotes sustainable drainage.

This was the case for a Durban-based homeowners’ association, where the Gabion Baskets project team was called in to assess an existing mattress installation that had failed over time. “This emphasises the point that the best designs will fail if the incorrect products – combined with poor installation technique – are employed,” explains Cheyne, adding that all of Gabions Baskets’ wire products are Class A galvanised as per industry standards to minimise the risk of corrosion.

Gabion Baskets’ site assessment revealed that the existing mattress – installed some 10 years ago – was rusting in places. There were also sections where the rock fill had started to wash out of the mattress, progressively undermining its integrity.

A new, wider mattress channel was recommended to disperse water more evenly, which was accepted by the client. For added protection, the wire system supplied includes a PVC coating to extend the mattress’ lifespan. The new system was successfully put to the test during some heavy downpours experienced in June 2023.

“Because they essentially ‘breathe’ with the environment, while holding the earth in check, gabions are the obvious choice for erosion control. But as we continue to see, designers are increasingly exploring their aesthetic side, while infrastructure planners recognise their value from a labour-intensive construction and employment creation perspective. It’s a win-win all round,” Cheyne concludes.

Prepping the site for the gabion