Constructing gabion foreshore protection is labour intensive, but also requires dedicated heavy lifting equipment and a supply of suitable rock fill. Construction of gabion units typically requires a large laydown area to enable rock stockpiling and cage assembly.
The order in which the rock filter and geofabric filter are laid depends on the site conditions. For a gabion mattress, the foreshore embankment is typically battered near to its angle of repose. A geofabric filter is laid over the slope and pinned in place. Rock filter layers are then placed over the geofabric. For a gabion wall, it is not unusual for the bottom level of gabion blocks to be placed first. The geofabric may then be draped over the back of the first layer of units, with rock filter placed and compacted in layers. The remaining gabion layers are completed in a similar fashion.
Gabions are supplied as pre-manufactured cages, which are assembled manually onsite. The gabion units are typically filled in place (if possible) to avoid unnecessary handling of filled cages. Wood or steel formwork is used to support the cages during filling operations. The gabions are partially filled using a loader or excavator.
Rocks are then placed by hand along the exposed faces and preformed bracing wires installed.
The gabion units are then completely filled with rocks, which are placed by hand to ensure the cages are fully filled and tightly packed. As outlined in Section 5.2.2 this is an integral part of the gabion function.
The gabions are then manually connected to adjacent units using wire twists.