The document link above (Modular Gabion Systems Design Guide) offers technical advice for engineers for basic wall design.
The design of the wall must take into account the height and the forces behind the wall if it is retaining. If it is a free standing wall the same principal applies in terms of stability. As a gabion wall relies on mass in general it should have a base of no less than half the height. This is dependent upon hydrostatic pressures and other forces behind the wall. If for a small garden wall of .5m high the forces will not be significant and a gabion depth of .5m deep should suffice. This is also true for a wall of 1m high, however it is recommended to consider the pressures which may be encountered and to ensure a drainage system is placed at the base, in particular if you use a geotextile to separate the earth from the gabion as the geotextile will slow down the flow of water creating pressure against the wall.
A 2m high gabion retaining wall would generally require a minimum base of 1m deep x 1.5m high with a .5m deep x .5m high upper tier. Or a 3m high gabion retaining wall would require a base of 1.5m deep, etc. The wall should be sloped into the embankment by 5-6 degrees. It is highly recommended when building retaining walls you employ the services of a geotechnical engineer to view the site in order to ascertain the potential forces behind the wall and to design a system which will be stable.
A gabion wall may be designed with a narrow base providing the designer employs earth anchors of some sort for retaining or internal posts set into concrete in the case of free standing walls.
As an example if you were to build a 6m length x .5m depth x .5m height. Start by laying a base panel (2 x .5m) where you want to start the wall. Attach a .5m x .5m panel to the base end using a .5m spiral. Next stage is to connect a side panel (2m x .5m panel) by using a .5m spiral to connect the end and 2 of 1m spirals to connect the side to the base. Do the same for the other side. Next place another base panel and a .5m x .5m (these are called diaphragms and are placed every metre to give the cage strength) panel at the other end of the first base panel and place another side panel and connect the diaphragm using a .5m spiral. Do the same for the other side. Continue this until the cage is complete.
Once the frame is complete you need to place .5m x .5m diaphragm panels between the ones already in place so that there is a diaphragm every metre of the cage. A .5m spiral is placed along the base and sides (3) for every diaphragm.
Note spiral ends should be then closed to prevent unravelling. Put in your stiffener wires next. In this size wall you should use 2 per 1m of cage, placed front to back, evenly in length and height.
Next place rocks. Usually preferred to place the larger rocks with flat face against mesh and any small rock can go inside the cage. Allow approximately 1.7 tonnes per m3 of cage. This cage example is 6m x .5m x .5m = 1.5m3. This example will require 1.7 x 1.5 = 2.55m3 (approximately).
The lid can then be secured using remaining spirals. If you were building a second tier on top of this wall of the same depth and length of the first you may use the lid of the lower tier as the base of the next, so continuing in a modular form. If the next tier is of different size cages you will need to treat this as a separate section. This upper tier will need to be connected to the lower section using either C rings or a larger diameter spiral available from us and called a spiral connector. These should be connected to front and back and the two ends. When building upper tiers it is preferable to use a brick work construction, this also gives the structure greater strength.
Gabion cages can be built as individual stand alone units or joined together together in rows using either C rings or spiral pins. Assembly guides can be found in the shopping section under information for each cage size.
Gabion rock should be selected so the rock placed against the mesh will not fall through. You will need rock which is 80mm - 200mm against the mesh for best results. Generally rock delived on-site will have a mixture from 40mm upwards. You may put the smaller rock inside the cages, away from the mesh faces, in fact this is a good idea in order to prevent small animals from making a home out of a gabion cage a smaller dense rock should be used. It is best to hand place the rock to prevent damage to the cage walls to minimise the gaps. The rocks shown on the following pictures are blue stone and sandstone. Both are fairly dense and will require roughly 1.7 tonnes per m3 of gabion cage.
To calculate your gabion m3 capacity for rocks, given that a typical gabion will require 1.7 tonnes of rock per m3: eg a gabion cage which is 2m L x 1m W x 1m H = 2 x 1 x 1 = 2 m3 x 1.7 = 3.4 tonnes of rock, or a cage which is 528mm L x 528mm W x 978m H = 0.528 x 0.528 x 1 = 0.28 m3 x 1.7 = 0.476 tonnes (half a tonne) of rock. Capacity does depend on the size rock so this is just a general guide.