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 Surface Armor for Erosion Protection
7.4.3 GABION MATTRESS
7.4.3.1 Description
A gabion mattress consists of a mesh container filled with cobbles or quarried stone.
Several firms market the containers and furnish technical assistance. Specialized equipment
or accessories are sometimes used on large jobs for efficiency, or on jobs requiring
underwater placement.
A form of gabion which is a hybrid between flexible mattress and adjustable armor is
the "sack" or "sausage," which can be filled faster than mattress or box shapes, making it
suitable for use in emergency situations. However, it makes less efficient use of material, and
is less common than traditional mattress or boxes.
7.4.3.2 Advantages
Since relatively small stones are used to fill gabion mattresses, a filter underlayment
is often not required. The hydraulic roughness is fairly low, especially if the gabions are
carefully filled or grouted. The appearance is more natural than some other materials, and
gabions are conducive to vegetative growth.
A gabion mattress is often used in conjunction with gabion dikes or retaining walls,
since the same construction practices can be used. A gabion mattress can be tailored to
irregular shapes in transitions from one type of protection to another, or around drains and
other structural features.
7.4.3.3 Disadvantages
A gabion mattress is less flexible than some concrete block mattresses. The mesh is
not immune to deterioration from the elements, although corrosion-resistant coatings or
grouting can be used to significantly alleviate potential problems of deterioration.
7.4.3.4 Design Considerations
Manufacturers have developed detailed guidance for every feasible application, and
this guidance should be obtained early in the planning process. Some general factors to
consider in design are discussed in the following paragraphs.
For given hydraulic conditions, a gabion mattress can be substantially thinner than a
riprap blanket. Recent model tests, as reported by Simons et al. (1984) provide guidance for
mattress thickness related to shear stress and velocity. Two conditions were analyzed:
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