The current design does not use any form of toe protection, nor is the structure placed on a filter.
As a result, the structure normally settles unevenly and rotates seaward into a scour trench. Because of
these movements, the allowable amount of differential settlement is sometimes exceeded, and the
resulting stress of the U-ties against the concrete blocks may crack or break them. Weak concrete
hastens the process so compressive strength tests should be performed on each batch of blocks before
construction to insure that high quality standards are met. Block breakage can eventually lead to
complete structural failure.
Quarrystone. A rubble breakwater is structurally similar to a rubble revetment (Figure 43). one
major advantage is that the structure does not fail when differential settlement occurs.
Time-tested and quite economical if suitable rock is available locally, stone has been used for
breakwater construction more than any other material.- of course, rock construction also requires heavy
equipment, which may have to be barge-mounted, resulting in higher costs.
Timber Piles and Brush. A brush breakwater is constructed with posts driven into the offshore
bottom, connected across the top with timber crossties, and filled with brush. Brush should be cut longer
than the space between the posts and placed parallel to the structure alignment. Not suitable for
permanent protection, it can be used as an energy absorber for temporary sheltering of new vegetation.
Used Tires and Timber Piles. Timber piles can be driven into the bottom so that every t ree piles
form a triangular pattern, and used automobile tires can then be stacked on the piles. Just above the top
tires, the triangularly grouped piles should be interconnected with planks bolted to the piles (Figure 44).
The structure, whose stability depends on the depth of pile penetration, has proven effective against mild
wave action.
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