ENVIRONMENTAL ENGINEERING
ZAMBIA RIVERBANK PROTECTION The wall begins to take shape Workers prepare the bank and foundation. The fence in the river is designed to discourage marine life, including crocodiles, from entering the construction zone
With the gabion mattresses installed, workers begin establishing the wire baskets for the initial 1 m high wall at the base of the retaining structure
WIRE AND STONE The strength of hightensile steel wire has been used for generations to form seemingly simple cubic boxes filled with rock to form structures commonly referred to as gabions. Modern-day fabrication techniques have significantly extended the design and application boundaries, says Clinton Cheyne, operations manager, Gabion Baskets, citing recent projects. By Alastair Currie 8
IMIESA October 2021
A section of the gabion mattress foundation at an advanced stage of completion. Note the steel plate working platform extending out into the river
D
erived from the Italian gabbione, gabion structures are designed to create a natural interface that blends in and essentially ‘breathes’ with the environment due to their approximately 75% or higher stone composition. The voids are there to intentionally ensure permeability, which is especially well suited to mass gravity retaining walls that must provide a degree of controlled drainage, whether in a bridge abutment role or for riverbanks or marine installations. Being rock-filled, water can pass through to a greater or lesser extent with the added incorporation of permeable or impermeable membranes, depending on the designer’s intention.
Zambezi River erosion In a recent riverine example, Gabion Baskets
secured an order for the supply of gabion baskets and mattresses for an erosion control protection project on a section of the Zambezi River near Chirundu in southern Zambia. This section borders a private property that extends to the riverbank. In addition to providing technical drawings and design advice, Gabion Baskets conducted in-depth training for locally employed workers, with a South African trainer deployed on-site during the key construction phases. “Before the preparation works could begin, though, the contractor first had to install a temporary 2 m high protective fence in the river, boarding the site in case a crocodile came to visit,” says Cheyne. “This was certainly a new take for us on an environmentally engineered solution.” For this project, a combination of gabion systems was installed, depending on
