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Correctly specified rock infill is required, in terms of quality, shape, hardness and size.
The appropriate rock type to fill your gabions and river mattresses. Experienced advice is offered regarding the best rock specifications or colour and shape for your needs.
Rock must be un-weathered without flaking or excessive weathering.
Gabions Size ;- 100 – 250 mm minimum (for 0.5 and 1m high baskets).
River mattresses Size ;- 100-2/3 the mattress thickness(to achieve at two layers of rock).
Do not use smaller rock fragments on the surface of either gabions or mattresses in river course situations. High water speed will remove any material that can pass through the mesh opening. Ensure that the rock size used is always bigger than the hexagonal/square mesh opening.
Smaller rock can be used within the centre of a gabion basket, however not to be a large amount so the strength of the filled gabion is compromised.
Softer rock and brick fragments to infill baskets are not recommended due to their water absorbing capacity, softening over time. Flat rock is usually inadequate as they do not provide the same mechanical interlock compared to using blasted angular rock, rounded river rock can be used, however can harm the environment after removal. It is much more difficult to obtain a flat facing during erection using rounded rock.
Rock density for gabions and mattresses should be minimum of 2.6 tons/m3, offering a void ratio of about 35%. When you add the 30% for waste/fines when dump rock is ordered we recommend ordering 2 T/m3 of rock.
Rock should be placed as close to the infill position as possible, when offloaded to reduce time wasted re-handling the rock.
Labor rates are 1-3 m3 per man per day, generally allow for 1 man/m3/day.
1. Rock supply, 2. Manual labor, and 3. Gabion/geotextile amount to approximately 33% each of the final completed gabion cost. For PVC coated baskets, allow about 20% extra to the overall cost of Galvanised gabions.
Different coloured and rocks type are available.