Gabions
1. General

Gabion (from Italian “gabbione” meaning"big cage”) is a cage or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineeringapplications. Present day gabions are rectangular baskets fabricated from a hexagonal mesh of heavily galvanized steel wire. The baskets are filled with rock and stacked atop one another to form a mattress or structure. Traditionally, the gabions were made out of stell wires. To prevent the corrosion of the gabion wires, in order to ensure long design life, the steel wires are galvanised and an external polymer coating is given to them. Behaviour of gabion structures depend mainly on the interlocking of the individual stones and rocks within the wire mesh for internal stability, and their mass or weight to resist hydraulic and earth forces. Gabions are a porous type of structure that can sometimes be vegetated.

2. Use of Gabions

There are numerous uses for these modular units. Some typical sue of Gabion structures are shown in Fig.1 to Fig.5 below:

3. Advantages of using Gabion Structures/Mattresses
(A) Flexibility:

The wire mesh construction permits it to tolerate displacements and settlements (including differential settlements) without fracture (Fig.6). This is especially important when a structure is founded on unstable ground or in an area where scour from waves or currents can undermine it.

(B) Strength:

The strength and flexibility of steel wire mesh is utilised to withstand and absorb the forces generated by retained earth or flowing water.

(C) Permeability:

Hydrostatic heads do not develop behind gabion structures because of their permeable nature. Their ability to combine drainage and retention functions make them ideal structures for slope stabilisation.

(D) Durability:

The efficiency of gabion increases with age since further consolidation takes place as silt and soil collect in the voids and vegetation establishes itself (Fig.7).

(E) Economy:

Gabion installation are more economical than rigid or semi-rigid structures due to following reasons:

    • Little maintenance is required.

    • Construction is simple, not requiring skilled manpower.

    • Suitable stone fill is normally available near site or from nearby quarries.

    • Minimum foundation preparation is required and the surface needs to be only reasonably plain.

    • Costly drainage arrangements are not required, as gabions are permeable.
(F) Ecology:

Since gabions permit growth of vegetation and maintain the existing environment, they provide attractive and natural building blocks for decorative landscaping.

4. Installation of Gabions

The steps involved in installation of gabion structures are as under:

(A) Transportation to site:

They are rolled in bundles and transported to site.

(B) Assembling:

The bundles are opened at site. To make then into units, the corners are wired together and diaphragms are fixed to the side panels. Empty units are then joined together along all adjacent edges, both horizontally and vertically. (Fig.8).

(C) Filling:

The assembled units are filled using rounded river shingles or quarry stones having a size slightly larger than that of mesh, so as to have minimum percentage of voids. Use of hard material with high specific gravity is recommended. The filling can be done after pacing at the required location or in some cases the filled units can be placed at the required location using mechanised means (Fig.9).

5. Videos :
5.1 Video on Assembling of Gabions
5.2 Video on Construction of Gabion Structures