Surface Armor for Erosion Protection
7.4.2 FABRIC MATTRESS
7.4.2.1 Description
Fabric mattresses made of synthetic material and filled with concrete grout, other
cohesive mixtures, or sand are available from various manufacturers. Tubular-shaped bags
are also available; these can be filled and placed either parallel to the streambank as a
bulkhead or perpendicular to the streambank as a dike, or can be used to fill scour holes or
undermined slopes.
7.4.2.2 Advantages
A fabric mattress is relatively easy to place, and fill material is often available locally.
Some designs have a low hydraulic roughness.
7.4.2.3 Disadvantages
Some designs provide only limited permeability and flexibility to conform to
irregularities in the bank.
7.4.2.4 Design Considerations
Many different designs are available. This allows the designer to discuss particular
site conditions with manufacturer's representatives in order to select a mattress which
emphasizes particular requirements, i.e., stability under hydraulic forces, filter and
permeability properties, flexibility, hydraulic roughness, resistance to deterioration, or
compatibility with vegetation. One form, intended primarily for filling with concrete,
integrates cables into the mattress to provide flexibility without separation even if the bag
deteriorates.
Potential subsurface drainage problems must be identified, and the installation
designed and monitored accordingly.
Use of a non-permanent fabric and fill material may be acceptable on the upper bank
if vegetation for permanent protection is planned. This approach has also been used on lower
banks and bed where the fabric is permanently underwater, and not subject to atmospheric
deterioration, vandalism, or impact from debris or vessels. Obviously some degree of
uncertainty exists when using perishable materials, so site conditions, expected project life,
and the consequences of failure must be carefully evaluated.
Polyester fabric has been reported to be subject to deterioration from the high pH of
concrete curing.
Anchoring the mattress to the bank slope is usually recommended by manufacturers.
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