where a fill is needed in advance of the existing shore. Finally, bulkheads are used for marina and other
structures, where deep water is needed directly at the shore (Figure 7).
Construction of a bulkhead does not insure stability of a bluff. If a bulkhead is placed at the toe
of a high bluff steepened by erosion to the point of incipient failure, the bluff above the bulkhead may
slide, burying or moving the structure toward the water. To increase the chances of success, the
bulkhead should be placed lakeward of the bluff toe, and if possible, the bluff should be graded to a
flatter, more stable slope.
Bulkheads protect only the land immediately behind them and offer no protection to adjacent
areas up- or downcoast, or to the fronting beach. In fact, their vertical faces reflect wave energy, which
may cause increased scour and could lead to a loss of any existing fronting beach. If the downdrift
beaches were previously supplied by erosion of the land now protected, they may erode even more
quickly. If a beach is to be maintained adjacent to a bulkhead, additional structures such groins or
detached breakwaters may be required.
Bulkheads may be either cantilevers or anchored (like sheet piling), or gravity structures (like
sand-filled bags). Cantilever bulkheads require adequate embedment to retain soil, and are used where
low heights are sufficient. Toe scour reduces their effective embedment and can cause failure. Anchored
bulkheads are usually used where higher structures are needed. They also require adequate embedment
(although less than cantilever bulkheads) to function properly, but they tend to be less susceptible to toe
scour.
Gravity structures eliminate the need for heavy pile driving equipment and are often appropriate
where subsurface conditions hinder pile penetration. However, they require strong foundation soils to
adequately support their weight, and they normally do not sufficiently penetrate the ground to develop
reliable soil resistance on the offshore side. Therefore, they depend primarily on shearing resistance
along the base of the bulkhead to support the applied loads. Gravity bulkheads also cannot prevent
rotational slides in materials where the failure surface passes beneath the structure. Their use, therefore,
is generally limited to relatively low heights where their cost is comparable to cantilever sheet pile
bulkheads.
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