Besides generating electricity, Kusile will also generate tons of coal ash, a bi-product that will need discarding in an ash dump with enough storage capacity to last 50 to 60 years. Since coal ash is considered a pollutant to ground water, the Department of Water and Sanitation (DWS) does not allow storage of this bi-product without ensuring the area is protected against contaminated water seepage into the environment.

Therefore, Eskom, in collaboration with Knight Piesold and various other consulting engineers, designed a durable composite liner system that will ensure the safety of the surrounding ground water for many years to come.

Forming an an essential component of this liner, engineered fabrics supplier Kaytech has provided huge quantities of its Neoweb and EnviroFix products for maximum environmental sustainability at the site.

Installed by contractor, WBHO, the multi-tiered composite liner system for the ash dump consisted of seven layers (top down);

• 2mm double-textured HDPE lining
• 750gsm nonwoven geotextile protection layer
• 100mm sand layer into which, in certain sections, Kaytech’s Neoweb was placed
• layer of Kaytech’s EnviroFix X1000 Geosynthetic Clay Liner (GCL)
• second layer of 2mm double-textured HDPE lining
• second layer of 750gsm nonwoven geotextile protection layer and finally
• 300mm selected G5 drainage layer.

Engineered linings

Neoweb, a high quality, sustainable and durable reinforcement solution, is a cellular confinement system manufactured from an HDPE alloy. When filled with soil, its honeycomb structure forms a composite system that stabilises soft soils and reinforces pavement structures.

In this particular linings system, EnviroFix will act as a secondary lining taking the place of at least 300mm of compacted clay as in conventional composite linings systems.

Locally produced, EnviroFix is manufactured by needlepunching a uniform layer of sodium bentonite between two durable outer layers of geotextile. Sodium bentonite is a naturally occurring clay mineral that swells considerably upon contact with moisture and, when this occurs under confinement, as in EnviroFix, a lining of very low permeability is produced. A proprietary heat-treating process (Thermal Lock) in the manufacture of EnviroFix, results in a GCL with increased internal shear resistance and long-term creep resistance.

Liner coverage

By completion of the ash dump, over a million square metres of EnviroFix X1000 GCL and 280 000m² of Neoweb 50mm will have been installed. The use of Neoweb, (in place of reinforced concrete), and EnviroFix, (in place of a compacted clay liner), has saved Eskom millions of Rands in time, construction expenses and costly transportation of imported materials.

Situated on a 1 355 hectare site between Bronkhorstspruit and Emalahleni, once fully operational, Kusile is expected to generate 4800MW of electricity, which will go a long way in alleviating the pressure on the South African grid. Kusile is considered Eskom’s most advanced coal-fired power plant project to date and once completed, is expected to be one of the largest coal-fired power stations in the world