of the material type and the structure's side slope.
Reflected sound from
steel produces a darker image than from concrete or stone, but concrete or
stone produces a darker image than wood. Coarse materials show up darker than
fine materials such as sand.
Also, the more nearly perpendicular the surface
is to the sound wave, the stronger the reflected signal and the darker the
image. A projection from the sea bottom, such as a displaced armor stone,
will show up as a dark area with a white area behind it because no signal is
reflected from the shadow.
The ocean bottom will show up as a lighter
area.
To produce good-quality records, an experienced SSS operator is a
necessity.
Prior knowledge of the kind of structure being inspected makes
interpretation much easier.
Fortunately, drawings are available for most
coastal structures. With experience in interpreting SSS records and a knowl-
edge of what the structures originally looked like, such things as changes
in slope and material composition, stones and armor units displaced beyond
the toe, and holes or cracks in the structure can be identified on the SSS
records.
Divers should be used following the initial SSS inspection. With a good
positioning system, divers can return and make visual inspections of the areas
where questionable images are found.
The advantage of combining SSS and
divers is that the diving operation can be reduced at a cost saving. Divers
need to inspect only a small percentage of the total length of the structure.
SSS may be the only tool needed in future inspections unless new problem
areas are found. Less diver verification will be required as experience is
gained in interpreting the SSS records.
AVAILABILITY:
Several SSS systems which could be used for inspecting coastal
structures are available for use within the Corps.
CERC has a 500-kHz system
with a sub-bottom profiler and is discussing using the system for inspection
work with several Corps Field Offices.
CERC's contact is Jim Clausner (601)
634-2009. Most of the following systems are being widely used so it is recom-
mended that a lead time of six months or more be allowed when requesting their
u s e , The Mobile District has a 500-kHz system and extensive experience using
it for inspecting coastal structures.
Their contact is James Reaves (205)
690-2704. Other Corps offices with this type of SSS system include: Philadel-
phia District, contact Bob Wagner (215) 365-5034, and Little Rock District's
Resident Office at Pine Bluff, Arkansas, contact Duane Combs (501) 534-0451.
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