Thinking outside the box GABION BASKETS EXPANDS THE BOUNDARIES of environmental engineering

An ancient technique perfected over the centuries for civil engineering works and military applications, the simple gabion has come a long way. Essentially rock-filled baskets, each assembled in either square, rectangular or other geometrical shapes, they come together to form an interconnected system. Typical applications include mass gravity embankment stabilisation, flood control and riverbank protection.

“Early renditions dating back to the Middle Ages show that a form of gabions was used for fortification works using wickerwork as the frame. From the late 19th century, the modern age has reinterpreted this with the use of advanced wire systems designed to optimise strength and maximise longevity in environmentally engineered applications,” Cheyne explains.

Engineering versus architecture

Founded in 2006 and headquartered in Johannesburg, Gabion Baskets provides holistic solutions in the multifaceted field of gabion systems. This capability encompasses manufacturing, design service recommendations, on-site installation training, project and programme management, and product development in distinct fields that encompass civil and environmental engineering, and architecture.

The key distinction between the two fields is the application environment, which has a direct bearing on the wire systems employed. For engineering works, such as bridge abutment protection, mass gravity retaining walls, weirs and river works, the standard specification internationally is the employment of Class A galvanised double-twisted hexagonal mesh wire, with or without a PVC/PE coating. This is used to form box gabion, gabion mattress and allied products such as sausage gabions. Rock-filled gabions typically have an approximately 30-35% void ratio that enables a degree of permeability and inherent flexibility.

In turn, architectural applications – which include building cladding, landscaping, freestanding feature walls and interior design elements – employ square welded mesh panel systems, which are supplied in a standard 3 mm or 4 mm diameter Class A wire specification.

Among its distinctive features are the precise tolerances that can be achieved, with perfectly flat faces. “However, architectural trends we’ve seen in Europe include the extensive use of curved welded panel extensions and bending of mesh at corners to follow structural contours or where joining is necessary,” says Cheyne.

Welded mesh, while robust, is not intended for engineered roles, being too rigid in terms of composition. This compares to hexagonal woven wire mesh systems, which have exceptionally high tensile strength and are purpose-designed for flexibility. Flexibility is especially vital in submerged riverine environments where gabion systems need to cope with varying water velocity, as well as scenarios like debris impact, pollution and abrasion. Here, a welded mesh structure would fail prematurely.

“It’s never a one-size-fits-all solution. Every site has its unique design requirements based on factors like the underlying geology and hydrology,” Cheyne continues.

“You must factor in the chain reaction (cause and effect) and take a systems approach. For example, a stormwater management intervention must take into account impacts on neighbouring properties, communities and structures. Without due consideration, you might fix the problem in one spot, but exacerbate it by

River Erosion Protection

Colonnades residential development, Gauteng Severe erosion on a stream section – caused by flood damage and upstream stormwater surges –threatened to undermine sections of the Colonnades residential development’s boundary walls. Gabion river wall protection works were constructed as a remediation measure, together with a weir further downstream to reduce water velocities. The works were completed in three phases, with Gabion Baskets providing design recommendations, installation training and product supply.

Mass Gravity Retaining Wall

Assagay Road, Durban

The severity of the storms that hit the eThekwini region during 2022 caused extensive landslides. A case in point is a property in Hillcrest, KwaZuluNatal, where a major embankment slope collapse swept away a section of private road linking a residential dwelling.

Working with the client’s consulting engineer, Gabion Baskets’ Durban office supplied design recommendations, project management and materials for the construction of an approximately 9 m high-mass gravity retaining wall. The intricate works included the incorporation of PVC pipes for stormwater drainage, as well as to minimise the risk of hydraulic pressure build-up behind the wall.

The wall incorporates specialist reinforced soil tie-backs using Gabion Baskets' Gab-tail product. The latter is a standard rock-filled gabion basket with a mesh tail extended horizontally back into the backfilled embankment.

Architectural Elements

Before: Site preparation on the severely eroded embankment, with the the downstream end as part of a sustainable urban drainage system

Free-standing wall: Fairbridge Mall, Brackenfell, Cape Town

Gabion Baskets’ Cape Town branch was approached by Isipani Construction to assist in the design of a welcoming wall at the Fairbridge Mall. The final design entailed the use of 50/50 mm aperture 3.15 mm welded mesh wire gabion panels, with charcoalcoloured selected rock chosen as the fill material. Internal steel support columns add structural integrity to the 1 m wide, integrated wall sections increasing downstream flows and the potential for flood damage on adjoining properties.”

Product research and development

Gabion Baskets constantly researches market trends locally and internationally to see where it can further refine its product offering to optimise performance and durability.

In this respect, during Q1 2023, Gabion Baskets will be making the shift from PVC to polyethylene (PE) coatings on its wire mesh products. These new wire coatings will be supplied by a Gabion Baskets Group company that is also responsible for the in-house production of its wire and welded mesh lines.

PVC wire coatings are employed globally as an extra layer of protection in highly corrosive applications that include marine projects, such as tidal erosion countermeasures, beach protection and rivers.

“PVC performs this job admirably, and can be offered in a range of colours, like tan and grey, to add an aesthetic effect. We’re now taking this level of protection a step further with the introduction of a PE coating. Latter benefits include greater resistance to cracking and hardening over time,” Cheyne explains.

From Q3 2023, Gabion Baskets will also be supplying the market with the option of Galfancoated wire produced via its group company, as part of a local content strategy. Galfan wire features a special zinc-aluminium alloy coating that provides greater corrosion resistance.

Another parallel development is the introduction of Gabion Baskets’ Associated Product Line to support SMME contractors. Examples include hog ring guns, hog ring clips, PPE and wheelbarrows.

“Wheelbarrows are one of those basic, universal items on-site. However, our research showed that standard versions tended to be unsuitable for gabion works. Our version has a more robust and balanced design well suited for transporting rocks. Key features include longer guide handles for better leverage and control, and a larger front wheel to cope with varied terrain,” says Cheyne.

Factory modernisation

To keep pace with increasing production volumes at its Johannesburg factory, Gabion Baskets has invested in high levels of mechanisation to streamline fabrication processes, along with ongoing skills development programmes.

In the factory, traditional steel wire lacing of gabion panels has now been replaced by the use of pneumatic hog ring gun clips that speed up the manufacturing process and achieve a neater finish. The same technique is now also being used on-site for gabion basket and mattress assembly, thus achieving a much stronger panel-to-panel and basket-to-basket connection.

“We now have dedicated production lines for woven mesh and welded mesh, respectively, each housed in their own dedicated buildings at our Johannesburg facility,” Cheyne explains. “This enables us to produce standard or custom products separately without affecting our main and common lines.”

African growth markets

Major growth across South Africa on key projects runs in parallel with export market opportunities within Southern Africa, as well as further afield on the continent.

Recent orders within the SADC region include two riverbank reinstatement and erosion protection projects for private properties bordering the Zambezi River in Zambia. These comprise the Musango Project, where a 300 m wall was constructed and completed in February 2022; and the Lolebezi Project, entailing the installation of a 500 m wall, which is currently ongoing. In both instances, Gabion Baskets provided design recommendations, on-site training, and PVC coated woven mesh river embankment systems.

Gabion Baskets is also receiving a growing number of enquiries from South African contractors working across Africa. Alongside this are orders from governmental clients that include the Botswana Defense Force, where some 500 gabion barriers were manufactured and supplied for its African Union mission in northern Mozambique. The product is similar to the European Hesco bastion.

These barriers are simple to assemble. Essentially, they are made up of interconnected fabric-lined welded mesh wire cages that can be filled quickly with any in situ material, like soil and rock. The concept borrows from the military fortification concept of old but takes it to a new level for ballistic protection. Another plus is that these barriers can also be rapidly deployed as flood mitigation measures.

The quest for excellence

“Our success to date has been based on our people. They truly are our biggest asset. It’s the engine room that drives us to innovate and add value by constantly refining our products and processes,” adds Cheyne.

“Given the environmental priorities, there’s huge demand for wire mesh systems, particularly in rivers. In parallel, our architectural clients are increasingly opting for welded mesh for interior and exterior design elements that harness the natural beauty of stone. By thinking out of the box, we continue to lead the market with fit-forpurpose solutions, in the process creating many opportunities for labour-intensive works on sites,” Cheyne concludes.

www.gabionbaskets.co.za

Ghana

Radioactive waste management project

The West African country has collaborated with the International Atomic Energy Agency (IAEA) to dispose of sealed radioactive sources. Under this Canadian-funded project, Ghana will receive technological and technical support for the construction of radioactive waste management facilities.

Zimbabwe

Disposal is the final phase for sealed radioactive sources when they have reached their end of life and are declared radioactive waste. However, disposal is not an easy task, because selecting the type of disposal facility depends on multiple factors, such as the type and quantity of radioactive waste; the existing and future environmental, geological, seismic and climate conditions; and available funds.

Energy crisis as Kariba Lake levels at 2% capacity

With a reservoir capacity of 180 600 hm3, the Kariba dam is the world's largest man-made dam that generates hydropower for millions of people in Zambia and Zimbabwe. The dam, finished in 1960, is on the Zambezi River, Southern Africa’s longest transboundary river.

As at mid-January, the dam's depleted levels will bring about drastic power cuts in both countries. Zambia and Zimbabwe both have their own power station on the north and south bank of the dam, with a generating capacity of 1 050 MW and 1 080 MW respectively, but both nations have seen their generating capacity reduced to less than 400 MW because of low reservoir levels.

Zesco, Zambia’s national power utility, announced that the limitation would affect its the ability to meet the system load/customer power demand, especially during morning and evening peak demand periods. It also said power outages would increase from 6 to 12 hours daily, although outages would be staggered into six-hour intervals to provide customers with some relief.

Zimbabwe is already facing 19 hours of load-shedding daily, with devastating effects on all aspects of life in the country. According to President Emmerson Mnangagwa, Kariba generates almost half of its power needs, which is why a reduction in its generation capacity immediately impacts on the economy.

Climate change has led to increased temperatures and lower precipitation in Southern Africa; on the other hand, the dam is badly in need of repair as the bedrock on which it was built has been eroded by routine operations, raising fears of a dam wall collapse. Both countries’ huge sovereign debts hinder their ability to pay for dam repairs and build the capacity to adapt to climate change.

For countries like Ghana, with limited amounts of radioactive waste, disposal could simply involve safe, secure and permanent placement inside boreholes, deep underground.The advantage of this system is that it allows for permanent disposal of the waste, rather than a storage solution.

The completion of an approved radioactive waste disposal facility in Ghana will enhance the human and technical capacity for the country’s nuclear power programme, which will enable the development of a nuclear power plant to meet the growing demand for electricity.

Mauritius

Ambitions to become a high-income country by 2030

The African Development Bank (AfDB) aims to promote private sector development to foster and build a more productive, sustainable, inclusive and resilient Mauritian economy. This will be done by further unlocking the country’s full potential in agriculture, ICT, finance, and the blue economy to move up the value chain.

Through supporting key economic, regulatory and institutional reforms, there will be a reduction in operational costs and this will create a more attractive environment for private investment.

Helping to eliminate bottlenecks that increase production costs and hinder companies’ competitiveness is another priority area for AfDB. The focus will be on infrastructure development, especially in the energy, water and transport sectors.

AfDB will support the strategic development and upgrading of costeffective infrastructure to increase Mauritius’ regional and international connectivity and competitiveness. Support to the energy sector will focus on transforming the country’s energy mix to facilitate its transition to green energy and implementing the national Renewable Energy Roadmap 2030.

The financier will consider climate change resilience in infrastructure projects to enhance sustainability and assist the country in mitigating hydrometeorological impacts on infrastructure.

As at 30 September 2022, AfDB’s active portfolio in Mauritius consisted of five operations, with a budget of US$262.29 million (R4.569 billion).

Egypt

Nine wastewater pumping stations for Fayoum Rowad Modern Engineering (RME) was awarded a US$12.2 million (R212 million) contract by Fayoum Water and Wastewater Company for sewerage networks and pumping stations in the Abu Shanab and Alagamein clusters at the new Qahafa wastewater treatment plant. Furthermore, a sewer network of approximately 53 km will be built, along with 17 km of forced mains.

The contract forms part of the Fayoum Wastewater Expansion Programme funded by the European Bank for Reconstruction and Development. The Fayoum Water and Wastewater Company estimates that the future facilities will have a capacity of 14 589 m3 of wastewater per day. The effluent is treated at the Qahafa wastewater treatment plant, inaugurated in 2010, which has a capacity of 60 000 m3/day.

The project will serve a population of 30 000 and the time for completion will be 18 months. It will contribute to reducing the pollution of Lake Qarun – the third largest freshwater lake in Egypt.

Nigeria

Extension works on Gombe drinking water system begin

The project, which is now entering its implementation phase, involves the extension of services and the construction of removal stations in the special development zone of the Gombe State capital, in Tunfure and Tashan Aduwa, along the Bauchi Road in the north-eastern parts of the country. It will also build a mini water system in Tabra, rehabilitate old water systems, and lay about 160 km of pipes for water distribution in the city.

At least 100 new isolation valves will be installed in the process and the 100 existing valves will be rehabilitated.

Jidadu Venture is carrying out the work, which includes upgrading the Wuro Juli water supply system in Gombe and installing 2 000 smart meters and 250 water meters at a cost of U$25.5 million (R444 million), with work expected to be complete by 2025. The Federal Government of Nigeria is supplying 30% of the funding, with Gombe State Government providing 70%.

In addition to securing access to drinking water in Gombe (with a population of 551 000), the challenge is to improve hygiene and sanitation services in this Nigerian state, particularly through handwashing. According to the World Bank, about 60 million Nigerians live without access to basic drinking water services, 80 million without access to improved sanitation facilities, and 167 million without access to a basic handwashing facility.