UFC 4-150-06
12 December 2001
Rubble-mound structures generally have a core covered with one to
several quarry stone underlayers that are protected with armor units of stone or
specially shaped concrete units. Breakwaters have a core material of randomly
dumped, well-graded quarry run, sand or coral. This material is generally impermeable.
Successive underlayers cover the core; the material in each successive layer is
carefully increased in size to prevent loss of the smaller-sized core material. Armor
units are placed on the outer surface to hold to core and the underlayers in place
against wave attack. Rubblemound revetments, groins, and jetties are similarly built in
that armor units hold the underlying material in place. Rubble-mound structures are
well suited to the coastal zone because they can absorb the forces of waves with
relatively minor damage even when design conditions are exceeded to a moderate
degree.
7-6.2
Vertical Front Structures. The types of structures of concern in this
chapter are gravity structures and sheet-pile structures. CEM Section VI-7-3 is the
nominal source.
7-6.3
Beach Fill Systems. Adding fill to a beach is an economical and
effective method to replace lost beach materials or to increase the size of an existing
beach. The added fill increases the backshore width and moves the high water line
farther offshore. The choice of fill type should resemble the original beach material and
the slope of the beach should also match the original slope as closely as possible.
Note that the cost and ease of beach fill as an erosion control method depends on the
rate of material loss from the beach. If fill is readily available from a nearby location,
the initial cost of refilling the beach would be low. However, regular refilling translates
into recurrent maintenance costs. See CEM Section VI-7-4 for information on beach fill
systems.
7-6.4
Floating Structures. Floating breakwaters are a special classification of
breakwater. A floating breakwater comprises a float, of sufficient size relative to the
wavelength, held in place by mooring lines fixed to anchors or to guide piles. Floating
breakwaters can be constructed of barges, pontoons, floating docs, or rubber tires, or
one can be specifically designed. The recommended source for more information on
this subject is CEM Section VI-7-5.
7-6.5
Pile Structures. As the most common type of deep foundation, piles are
used to transmit loads through upper weak and/or compressible soil strata to underlying
competent zones. These include driven piles, drilled piles, drilled piers/caissons, sheet
piles (for containing fills), and fender piles for docking. Piles also provide support in
areas where shallow foundations are impractical, such as underwater, in close proximity
to existing structures, and other conditions, and to provide uplift resistance and/or
lateral load capacity. The performance of a deep foundation is highly dependent on the
installation procedures and quality of workmanship. Forces on piles and piers and pile
design are addressed in the recommended source for information on this subject, CEM
Section VI-7-6.
7-4
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