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 a destructive one. A newly developed underwater Schmidt hammer concrete
hardness tester is becoming available to provide a better measure of surface
compressive strength. The cross sections of steel H-piles can be measured
more accurately than wood or concrete structures can with simple instruments.
1 . 4 . 4 . 2 L e v e l I I I . Level III efforts are used when better data is
desirable to perform structural assessments. A small sampling of more
precise measurements are taken, where possible, with sophisticated
instruments.
On steel H-piles and steel sheet piles, metal thickness measurements are
made with a pulse echo ultrasonic thickness meter. Areas to be measured are
cleaned so as to provide at least a square inch of smooth surface at each
spot to allow the instrument's sensor to be held in direct firm contact with
the metal. Many thickness measurements can be made rapidly once the
cleaning has been done. Thickness measurements made with a pulse echo
ultrasonic system will be made at a rate of 30 to 60 piles per day.
Measurements-in wood piles are performed with another type of ultrasonic
transmission equipment. This system measures the undamaged cross-sectional
area of wood piles in increments of fourths. One diver moves the
transmitter and receiver sensor assembly around and up and down the piles
fairly rapidly, while a meter at the surface, which is wired to the sensor,
indicates the undamaged pile area and its elevation. Only the largest pile
growth has to be removed, making this type of measurement very efficient.
With the exception of the hardness test, using the underwater Schmidt
hammer, no specific quantitative methods are available to determine the
s t r u c t u r a l i n t e g r i t y o f c o n c r e t e p i l e s . Therefore, evaluating the physical
properties of concrete underwater is limited to experience judgments with
the use of simple instruments. The number of measurements per day used for
concrete piles is also in the range of the effort used for cleaning alone.
The number of measurements per day on concrete bulkheads is similarly
considered to be in the same range as for cleaning bulkheads of all
materials.
1.4.5 Photo Documentation. Color photographs are taken during the
inspection to document facility configuration, representative damage or
deterioration, both typical and extraordinary marine biofouling, pile
splices or joints, cross-bracing and previous repairs. Photographs should
include samples of structural members at the mudline, tidal zone, and midway
between both areas. Turbid water conditions can be overcame for close-up
photos by the use of clear water boxes and wide angle and close-up lenses.
Underwater television can be useful to document general observations and to
have a real-time display available on the surface. Color TV is preferable
to black-and-white because the colors provide more distinction between types
of corrosion and biofouling than do the shades-of-gray. However the video
image lacks the resolution and color rendition qualities of still
photography. Color TV should be used to augment color still photography
rather than to replace it. Both types of visual records are useful to the
structural analyst, particularly one who may not be part of the dive team.
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