REVETMENTS
The armor layer of a revetment maintains its position under wave action either through the weight or
interlocking of the individual units.
Revetments may be classified as flexible, semi-rigid, or rigid.
Flexible armors, such as quarrystone, riprap, or gabions, retain their protective qualities even if the
structure is severely distorted, such as when the underlying soil settles, or scour causes the toe of the
revetment to sink. A semi-rigid armor layer, such as interlocking concrete blocks, can tolerate minor
distortion, but the blocks may be displaced if they are moved too far to remain locked to the surrounding
units. Once one unit is completely displaced, such revetments have little reserve strength and
displacement will generally continue to complete failure. Rigid structures may be damaged and fail
completely if subjected to differential settlement or the loss of support by underlying soil. Grout-filled
mattresses of synthetic fabric and reinforced concrete slabs are examples of rigid structures.
Rubble
Rubble revetments are constructed of one or more layers of stone, or concrete pieces derived from
the demolition of sidewalks, streets and buildings. Stone revetments are constructed of either two or
more layers of uniform-sized pieces (quarrystone), or a gradation of sizes between upper or lower limits
(riprap). Riprap revetments are somewhat more difficult to design and inspect because of the required
close control of allowable gradations and their tendency to be less stable under large waves. For that
reason, graded riprap revetments should be used with caution, but they are acceptable for the majority of
low cost shore protection applications. Quarrystone structures are more easily designed and inspected
and are recommended.
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