A gabion is a netted (wire mesh) box (Fig-1) filled with aggregate material – compatible with the size of the net mesh – serving as gravity units forming retaining structures.
It provides a means to contain such aggregates of small and diverse sizes which cannot be used to construct gravity retaining walls of the masonry type. When such materials are put together and ‘contained’, they are made to serve their gravity role efficiently and economically.
The large steel wire mesh boxes (Fig-2), usually rectangular in shape, but variable in size, are filled with low grade or waste stones – economically sourced at site. The gabion units can be handled as building blocks, to erect structures with unique flexible characteristics which enable them to be put to use in curved and inclined alignments. Its inherent flexibility is a striking feature which enables it to adapt itself to a change in shape without distress. It will yield to any earth movement, and in the process of undergoing deformation, still remains structurally sound. This is clearly a feature with distinct technical advantages over a conventional rigid or semi-rigid structure – particularly at sites where heavy settlements are anticipated.
The modern form of gabions was evolved by the Italian firm MACCAFERRI who are the world leaders in this field.
What Are The Advantages of Gabion?
The principal features of a gabion structure may be cited as durability, flexibility and permeability. As regards durability, over a period of time when the mesh starts to corrode, silt and vegetation will combine with the rock filling, forming a permanent structure which can stay intact even when the mesh has fully disappeared. Mention has already been made of gabion’s intrinsic feature of flexibility which enables it to adapt itself to any in-situ soil profile.
What sets gabion apart from dry stone walling is that, the wire mesh being extremely strong in tension, the gabion structure can withstand a degree of tension which is quite impossible with dry stone walling. In this respect it must be emphasised that the wire mesh shell is not merely a frame to contain the stones; it serves as reinforcement for the entire structure.
The high permeability of gabion fill ensures automatic drainage, which obviates the need for measures such as the provision of weep holes.
Besides everything else, gabions are considerably cheaper than their more conventional alternatives in terms of both material and labour.
What are the Uses of Gabions?
Gabions are used in
1) Retaining structures, including retaining walls, revetment and toe walls to embankments and cuttings,
2) Anti-corrosion structures, such as sea walls, river bank defences, canal banks, dams, weirs, groynes and for the protection of reservoirs and lakesides.
Examples of Gabion Uses
Some of the uses of gabions are illustrated in the following figures.
1) A retaining wall under a road embankment laid well below a possible slip surface is illustrated in Fig-3. The deep gabion on the right serves as a drain to intercept water before it can pass under the roadway.
2) Fig-4(a) shows the creation of a road embankment within gabion walls.
3) Fig-4(b) is an example of how gabions lend themselves famously for use in landscaping.