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 transducers operating at about 30 KHZ are attached to a rack or frame at a fixed distance, one above
the other. This assemblage ("sonic probe") is manipulated by a scuba diver to provide a scan of the
pile from the surface of the water to the mud line. A surface technician, who is in telephone contact
with the diver, collects and records the data. The data is then computer analyzed to determine cur-
rent load carrying capacity of the piles. Under average conditions, one two-man crew can test ap-
proximately 100 piles per day.
7.2.3 Remedial Treatments.
7.2.3.1 Determining Serviceability. The effect of the loss of wood on pile
strength is similar to that for poles. The sonic testing method is one way in which the remaining
strength of a pile can be assessed. The decision on whether the pile should be left or replaced is best
left to an engineer familiar with wood design and expected loads. In those cases where the pile is
decayed or infested with marine organisms, but it is still capable of bearing the expected loads,
remedial m-place treatment is necessary.
7.2.3.2 Decay Prevention. The procedures discussed for the ground line treat-
ment, void treatment and fumigation of poles can also be applied where appropriate to piles.
Since pile tops are commonly "cut-off" after driving and top decay results, remedial treatment is re-
quired. This cut-off area should be treated with a preservative and then capped as described in Chap-
ter 5. These treating recommendations require flooding the exposed surface with hot creosote (150
to 200 degrees fahrenheit), pentachlorophenol in diesel oil, or copper naphthenate. A water-shed-
ding cap is then applied. None of these preservatives penetrate the wood deeply.
Materials used for capping piles include coal tar-roofing cement, galvanized metal, copper sheath-
ing, heavy roofing felt, heavy plastic, Noah's pitch, hot asphalt, and preservative-treated plywood.
One effective capping device is coal tar-rooting cement held in place by a fiberglass mesh cloth. To
cap a pile by this method, trowel a thick layer (1/2 inch) of cement on top, place two layers of
fiberglass mesh on the cement, nail the mesh to the pile, and finish with an additional coat of ce-
ment. This patch remains flexible and resists water penetration into the untreated wood below.
Galvanized metal, roofing felts and plastic sheets make effective caps when applied in conjunction
with chemical treatments. Without a preservative, condensation or leaks can create ideal conditions
for decay beneath the cap. The material should be cut with at least a 2-inch overlap to permit the
edges to be folded down and fastened to the pile sides with galvanized roofing nails or bands.
Noah's pitch or hot asphalt may be applied to pile tops before addition of a water-shedding cap.
However, these materials only penetrate the wood to a shallow depth and are of little use if the cap
leaks.
Preservative-treated plywood makes a simple but effective capping device. Two narrow strips of
treated wood are nailed to the pile top, and the plywood cap, cut to a slightly larger diameter than
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