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 gravity-type wall. Gabions 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. Gabions are considered to be a "hard" structural solution that has minimal habitat and aesthetic value.
Gabions are used to slow the velocity of concentrated runoff or to stabilize slopes with seepage problems and/or non-cohesive soils. Gabions can be used at soil-water interfaces, where the soil conditions, water turbulence, water velocity, and expected vegetative cover are such that the soil may erode under the design flow conditions. Gabions can be used on steeper slopes than riprap and are sometimes the only feasible option for stabilizing an area where there is not enough room to accommodate a "softer", vegetated solution.
Gabion Retaining Wall
Some advantages of gabion walls are:
Ease of handling and transportation
Speed of construction
Flexibility (Gabions tolerate movement)
Permeability to water (Good drainage)
Gabions offer an easy-to-use method for decreasing water velocity and protecting slopes from erosion.
Gabion (greater than 1' in height) and mattresses (less than 1' in height) consist of rectangular units fabricated from a double-twisted hexagonal mesh. Gabions and mattresses are divided into cells with diaphragms (usually spaced at 1 meter or 3’ intervals), whose function is to reinforce the structure. Filled with stones, both of them become large, flexible, and permeable elements from which a broad range of structures may be built. The mesh, except for the diaphragms, is reinforced on all edges with wires of a larger diameter to strengthen the gabions and facilitate the assembly and installation.
They are also widely used for hydraulic and geotechnical control such as retaining walls, riverbank protections, weirs, channel linings, and so on.
Gabions and mattresses are non-traveling mesh made by twisting continuous pairs of wires through three one-half 1/2 turns to form hexagonal-shaped openings which are then interconnected to adjacent wires to form hexagonal openings. For easy handling and shipping, the gabion and mattresses are supplied folded flat. A color stripe applied on the side of each folded gabion identifies the size.
For easy handling and shipping, gabions are supplied folded into a flat position and bundled together. Gabions are readily assembled by unfolding and binding together all vertical edges with lengths of connecting wire stitched around the vertical edges. The empty gabions are placed in position and wired to adjoining gabions. They are then filled with cobblestone-size rock (10-30 cm in diameter) to one-third their depth. Connecting wires, placed in each direction, brace opposing gabion walls together.
The wires prevent the gabion baskets from "bulging" as they are filled. This operation is repeated until the gabion is filled. After filling, the top is folded shut and wired to the ends, sides, and diaphragms. During the filling operation live rooting plant species, such as willow, may be placed among the rocks. If this is done, some soil should be placed in the gabions with the branches, and the basal ends of the plants should extend well into the backfill area behind the gabion breast wall.
Several different design configurations are possible with gabions. They may have either a battered (sloping) or a stepped-back front. The choice depends upon the application, although the stepped-back type is generally easier to build when the wall is more than 10 feet high. If large rocks are readily accessible, inexpensive, and near the proposed site, then their use in the construction of a rock wall may be preferable. On the other hand, if rock must be imported or is only available in small sizes, a gabion wall may be preferable.
Since gabions are used where erosion potential is high, construction must be sequenced so that they are put in place with the minimum possible delay. Disturbance of areas where gabions are to be placed should be undertaken only when final preparation and placement can follow immediately behind the initial disturbance.
Where gabions are used for outlet protection, they should be placed before or in conjunction with the construction of the pipe or channel so that they are in place when the pipe or channel begins to operate.
Gabions should be inspected on a regular basis and after every large storm event.
All temporary and permanent erosion and sediment control practices shall be maintained and repaired as needed to assure the continued performance of their intended function.
All maintenance and repair shall be conducted in accordance with an approved manual.
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