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A facing or veneer of stone, concrete, or other materials constructed on a sloping embankment, dike, or beach face to protect it against erosion caused by waves or currents. The revetment may be a rigid cast-in-place concrete structure; but more commonly it is a flexible structure constructed of stone riprap or interlocking concrete blocks. It is sometimes an articulated block structure where the armor blocks are set in a form known as a flexible carpet; that is, the blocks interlock for stability, but the interlocking makes them flexible enough to respond to settlement of the underlying soil. A flexible revetment provides protection from exterior hydraulic forces, and it also can tolerate some settlement or consolidation of the underlying soil.
A typical revetment might employ stone riprap as the armor material (see illustration). A revetment typically has three major components: (1) the armor layer, which resists the wave or current-induced hydraulic forces; (2) a filter layer under the armor layer to allow water seepage out of the underlying soil without the removal of fine soil particles; and (3) a mechanism to stabilize the structure toe. Toe stabilization is particularly important where waves break on the structure, but may not be necessary if the revetment extends to sufficient depths where hydraulic forces will not erode the toe of the slope. The design water level (see illus.) for the structure may be higher than the normal water level during nonstorm conditions. If the revetment is exposed to waves that will break and run up the face of the revetment, the upper extent of the revetment must be sufficiently high to counter the force exerted by the waves.
Although stone riprap is the most commonly used material for revetment armor layers, a wide variety of other materials have been used, including cast-in-place concrete and poured asphalt, wire bags filled with stone (gabions), interlocking concrete blocks, soil cement, cement-filled bags, interlocked tires, woven wooden mattresses, and vegetation (only used for surfaces exposed to very low waves or slow-moving currents). See Retaining wall, River engineering