Sandgrabber
Wave Height Range: Below five feet.
A patented configuration of interconnected concrete construction blocks (Figure 71), the Sandgrabber is
a device that allows for some differential settlement of the blocks by using U-shaped, galvanized-steel
connecting rods. The hollow blocks allow waves to wash sand through, trapping the coarser, water-borne
particles behind the structure. The Sandgrabber must be installed by a franchised contractor.
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. This can eventually
lead to complete collapse of the structure. Weak Concrete hastens the process, so compressive strength
tests should be performed on each batch of blocks before construction. A precaution when using a
Sandgrabber, or any other breakwater, is to avoid downdrift erosion damages. Backfilling with sand
should prevent any potential problems.
Quarrystone
Wave Height Range: Above five feet.
A stone breakwater is structurally similar to a stone revetment (Figure 72) and stone sizes should
also be selected by using Equation (17). However, the stability coefficient, KD, should be selected from
Table 16, rather than Table 12.
Table 16
105
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