The primary advantage of a rubble revetment is its flexibility, which allows it to settle into the
underlying soil or experience minor damage and still continue to function. Because of its rough surface,
it also experiences less wave runup and overtopping than a smooth-faced structure. The primary
disadvantage is that placement of the stone or concrete armor material generally requires heavy
equipment.
To insure good performance, prepare the existing ground to a stable slope. In most cases, the
steepest recommended slope would be 1 vertical on 2 horizontal (1:2). Fill material should be added
where needed to achieve a uniform slope, but it should be free of large stones and should be firmly
compacted before revetment construction proceeds. Properly sized filter layers should be provided to
prevent the loss of the slope material through voids in the revetment stone. If using filter cloth, an
intermediate layer of smaller stone below the armor layer may help distribute the load and prevent
rupture of the cloth.
No individual armor unit should be longer than three times its minimum dimension. In other words,
avoid using plate-like or cylinder-shaped pieces; stones should be angular and blocky, not rounded. The
toe of the revetment should be located one design wave height (but at least three feet) below the existing
grade line to prevent undercutting in lieu of deep burial, a substantialsacrificial berm of additional rubble
(with filtering) should be provided at the toe.
Quarrystone and Riprap
Wave Height Range: Above five feet (Quarrystone).
Below five feet (Riprap).
Stone revetments are a proven method of shoreline protection (Figure 42). They are durable and
can be relatively inexpensive where there is a local source of suitable armor stone. Quarried stone should
be clean, hard, dense , durable, and free of cracks and cleavages. Figure 43 shows a typical cross section
of a stone revetment. The weight of the armor stones should be determined by the following formula as
given in the Shore Protection Manual [U. S. Army Corps of Engineers (1977c)].
W = wrH3 / KD(Sr 1)3 cot θ
(17)
Where W = weight of an individual armor stone (pound);
Wr = unit weight (saturated surface dry) of the rock (lbs/ft3)
H = wave height (feet);
Sr = specific gravity of the armor stone (wr/ww); where ww = 64.0 lbs/ft3 for salt water and 62.4
lbs/ft3 for fresh water
Cot θ = slope of the structure expressed as horizontal units/vertical units
KD = Stability coefficient from Table 12.
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