stone revetments are time tested, highly durable, and often the most economical where stone is locally
available.
The primary advantage of a rubble revetment is its flexibility, which allows it to settle into
underlying soil or experience minor damage and still continue to function. Because of its rough surface,
a rubble revetment 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.
Prior to construction, the existing ground should be stabilized by grading to an appropriate slope.
In most cases, the steepest recommended slope would be 1 vertical on 2 horizontal (1on 2). Fill material
should be added as needed to achieve uniformity, but it should be free of large stones and firmly
compacted before revetment construction proceeds. Properly sized filter layers should be included to
prevent the loss of slope material through voids in the revetment stone. When using filter cloth, an
intermediate layer of smaller stone below the armor stone may help distribute the load and prevent
rupture of the cloth. The revetment toe should be located about one design wave height (but at least three
feet) below the existing bottom to prevent undercutting. In lieu of deep burial, a substantial sacrificial
berm of additional rubble (with filtering) should be provided at the toe.
Quarrystone. Stone revetments, a proven method of shoreline protection, are durable and can be
relatively inexpensive where there is a local source of suitable armor stone. Such stone should be clean,
hard, dense, durable, and free of cracks and cleavages.
If graded stone filter material is used, it generally will be much finer than the armor stone. An
intermediate layer of stone between the armor and filter, one-tenth as heavy as the armor units, may
provide the necessary transition to the filter material.
Concrete. A concrete rubble revetment utilizes a waste product otherwise difficult to dispose
of in an environmentally acceptable manner. The concrete should have the strength to resist abrasion by
water-borne debris and ice pressure. In addition, all protruding reinforcing bars should be burned off
prior to placement. Numerous concrete rubble revetments have failed in the past, usually because of
neglect of filter requirements.
Concrete Block Revetments
Concrete blocks, many of them patented, have various intermeshing or interlocking features
(Figure 23), and the advantage of a neat, uniform appearance. Many units are light enough to be installed
by hand once the slope has been prepared. Their disadvantage is that interlocking between units must be
maintained. Once one block is lost, other units can dislodge, and complete failure may result. A good,
stable foundation is required since settlement of the toe or subgrade can cause displacement of units and
ultimate failure. Also, some concrete bl6ck revetments have smooth faces that can lead to significantly
higher wave runup and overtopping.
For maximum effectiveness, concrete block systems should only be placed on a stable slope with
the toe buried at least three feet below the existing ground line. Fill materials beneath the revetment
should be uniform and well compacted and an adequate filter system, preferably with a properly sized
woven filter cloth, should be provided. All concrete must be high quality; standard building blocks will
probably deteriorate too quickly. Finally, blocks should not be used where they may be stolen or
damaged by waveborne cobbles, ice, or debris.
33
Previous Page
