Gabion walling is being used to retain fill and grout that is to be placed under an existing bridge. The bridge is no longer required and requires additional support. The access was very restricted and the gabions had to be filled from under the bridge and from the road on top of the bridge.
Gabions are free-draining walls constructed by filling large baskets with broken stone. The baskets are made from galvanised steel mesh, woven strips, or plastic mesh. They can also be made from wickerwork, bamboo slats, nylon or polypropylene. A typical basket is rectangular with dimensions of about 50 cm by 15 cm.
Retention is achieved form a combination of the stones weight, and its interlocking and frictional strength. The wall face is battered at approximately 6 degrees from the vertical. The maximum height is approximately 10 m. They are constructed with either a stepped face or a stepped back.
The permeability and flexibility of gabions make them suitable where the retained material is likely to be saturated and where the bearing quality of the soil is poor. Wire mesh gabions have two forms, baskets which are used for walls and mattresses which are used for revetments and river linings.
The actual shape of gabion retaining walls is trapezoidal. However the outer and inner faces may be straight or steeped. The width of the horizontal tread of the steps should not exceed the depth of the gabion. Walls can have a plane outer face, preferably built to a batter for appearance and to increase resistance to overturning. Similarly walls with stepped faces should be tilted towards the backfill. Counterforts or buttresses may be incorporated in the construction.
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