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 7.1.3 Determination Of Serviceability. As the integrity of a wood member is destroyed
by biological agents, its ability to withstand the load it was designed for is diminished. As more and
more wood is destroyed, the structure becomes weaker. With poles, the location of the wood that is
destroyed is perhaps more important than the amount of wood destroyed. The outer 44% of the pole
radius contributes most (about 80%) of the bending strength. Therefore, decay in the core of the
pole will reduce strength substantially less then if the outer shell is destroyed.
The National Electrical Safety Code specifies the allowable stress for poles when installed and at re-
placement for different grades of construction. Depending on the amount and location of wood lost,
it can be determined if the pole still meets the safety code requirements. Poles which do not meet or
exceed minimum requirements are generally marked for replacement. Others can be field treated to
arrest the wood destroying organisms.
Rural Electrification Administration have determined it is more cost effective to apply remedial
treatments to poles, that show signs of biological (decay or insect) damage but are still capable of
carrying the required loads, than to replace them. A number of different treatments are available
through the commercial firms who inspect and treat poles. NAVFAC Specification TS-20312
provides criteria for contract writers. The cognizant PMC can provide further assistance and a list
of reputable pole maintenance firms.
7.1.4.1 Ground Line or Bandage Treatment. These treatments have long been
used to control surface decay in the outer shell of poles. Preservatives used include water soluble ar-
senicals and fluorides, alone or mixed with creosote, pentachlorophenol or dinitrophenol and potas-
sium bichromate. Other materials may be used depending on the formulator. The formulation is
either a liquid or a paste. These preservatives diffuse into the wet wood. They can be brushed on or
injected 2-1/2 inches into the wood with a hollow needle. Thoroughly brushing on a thick coat of
preservative assures that the surface is well treated and that all crevices are filled. The outer wrap,
often black polyethylene film with a paper back, should be durable and extend from slightly above
to 18 inches or more below the ground line. The layers are overlapped and the wrap is fastened
tightly to the pole in order to shed water. Some preservatives are incorporated in the wrap. The
wrap should not be damaged as the backfill is being replaced.
Before treatment, the surface to be treated should be cleaned of any decayed or loose wood. No
more sound wood than necessary should be removed. All debris should be removed from the ex-
cavated area around the pole.
NAVFAC TS-20312 specifies the following for ground line treatment:
GROUND LINE TREATMENT: A preservative material approved in paragraph 7.0, Section
00004, shall be thoroughly and evenly applied, at the maximum allowable thickness specified on
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