Nonwovens supplier Fibertex SA’s geosynthetic sand containers (GSC-bags) will ensure the protection of the natural environment in the construction of a revetment structure at uMdloti beach, on KwaZulu-Natal’s north coast.
Fibertex SA technical manager Gerard Dirks explains that coastal erosion is becoming more prevalent as a result of rising sea levels and changes in global weather patterns. It has also become increasingly important to have well-engineered, durable and easily manageable coastal protection structures in place in order to manage this.
“Although using large sandbags as structural components of revetments is not new in environmental protection, Fibertex has made a substantial investment in designing and manufacturing a robust GSC system with GSC bags that are a lightweight, durable and workable geosynthetic substitute for traditional revetment systems that use rock and seawalls that use concrete and reinforcing steel.”
Dirks highlights that these GSC bags were manufactured at Fibertex’s KwaZulu-Natal plant in Hammarsdale, especially for this installation.
The function of a GSC bag is to allow the free passage of water through the porous structure of the fabric and into the sand it carries, to absorb wave energy, while retaining the sand fill in the bag. This is unlike hard concrete structures, which predominantly protect by means of wave energy reflection and which could have a negative long-term impact on adjacent structures.
GSC bags consist of a strong porous base fabric, which is mechanically needle-punched together with a coarse anti-abrasion and vandal resistant cover layer (AVL). This robust fabric combination offers a flexible structure that is able to retain course fill medium-size sand, while allowing the free passage of water.
Dirks notes that Fibertex AVL geotextile sand containers, which are manufactured from highly ultraviolet- (UV-) stabilised virgin polypropylene fibres, can withstand the effects of repeated wave attacks in harsh coastal environments and are, thus, an ideal soft solution to beach rehabilitation and coastal protection.
“Geotextiles used in the manufacture of GSC bags are required to withstand the effects of different environmental conditions from the geotextiles used for conventional separation, filtration, drainage and protection. “The Fibertex team has given particular attention to critical factors in the development of this system, including abrasion, perforation, puncture and UV resistance, tensile strength and elongation, as well as permeability and drainage.”
GSC material selection is critical to the long term stability of the entire structure. In the case of coastal protection applications, where high energy bi-directional flow conditions are encountered, needle-punched staple fibre geotextiles are preferred. Dirks stresses that they have proven to be durable and the staple fibre geotextiles do not delaminate under the harsh flow conditions expected from wave action.
Fibertex has selected polypropylene fibre, with notable frictional and low density characteristics, as the basis for manufacturing its GSC fabrics. Polypropylene has better performance to weight ratio than other more dense polymers, such as polyester. Although polyester is a strong, durable polymer, polypropylene is preferred globally in the manufacture of heavy grade and voluminous GSC fabrics.
Other important properties for appropriate product selection include the design of the revetment structure, where environmental influences such as wave amplitude, wave period and wave direction need to be taken into account.
Size selection of GSC bags for each application is also critical. Smaller GSC bags might be sufficient for less harsh conditions, but direct wave attacks often require a larger, more stable GSC bag. The correct installation procedure and optimal filling and closure of GSC bags prevent free movement of the bag, to ensure the long-term stability of the structure.
Fibertex GSC bags, which are available in sizes between 200 kg and 4 000 kg, can be used in riverine, lagoon and coastal protection works, depending on specific environmental and engineering requirements of the designed structure.