Specification and Treatment
of Timber Piling QA/QC when it comes
Timber piles have been utilized over the world for thousands
of years. History reveals that the Neolithic tribes
in Switzerland used natural (untreated) logs as pilings
to support homes built on the region’s shoreline for almost
6,000 years. Archeologist have found similar use of timber piling
for bridges spanning the Tiber River dating back to 620 B.C.
Standards exist today to ensure replicable strength values and
durability that provide a consistent level of quality and service for
the marketplace.
Timber piles are a unique product in that they are made from a
natural material and are subject to variations in size, straightness
and strength. In North America, there are two predominant species
used for timber piles, Southern Pine and Douglas Fir, which are
protected by preservatives to ensure long service life.
Forests are managed for 35-plus years to create timber piles.
Sustainability is built in, in that we grow more trees than are harvested
and the enhanced durability of preservative-treated timber
pilings allows forests more time to produce mature trees. While
growing timber for piling, it is important that the material characteristics
be reproducible. The American Society for Testing and
Materials (ASTM) first developed standards for timber piles in
1915, titled ASTM D25, Standard Specification for Round Timber
Piles. These rules established a minimum criteria to ensure that
each tree produced for piling creates a replicable timber pile and
to a natural material
performs as intended. Standard D25 is updated periodically and
focuses primarily on the quality, straightness and size of piling.
ASTM D25 specifies that piles shall be of any species of wood for
which strength values are provided for in ASTM D2555, Standard
Practice for Establishing Clear Wood Strength Values. ASTM D25
ensures the quality of each pile by requiring that each pile be of
sound wood, establishing a minimum number of growth rings per
inch and a minimum percentage of summerwood in the outer 50
percent of a pile tip. The standard also provides requirements for
the straightness of each pile, spiral grain and the size and number
of knots allowed to ensure consistency while accommodating
minor variations in this naturally grown product.
The standard also addresses the size of timber piles by providing
minimum tip and butt dimensions for each of the designated
lengths. These minimum dimensions ensure a predictable taper for
each pile so designers can calculate the diameter at any location
along its length. Tables are provided for both Southern Pine and
Douglas Fir that allow a designer to specify a tip circumference or
butt circumference. For an end bearing pile, a tip circumference is
specified. The table provides a corresponding minimum pile butt
circumference, measured three feet from the large end (butt) of the
pile, based on the designated length. Conversely, for piles that rely
primarily on skin friction, a butt circumference is specified. The
table provides a corresponding minimum tip circumference, based
By Kevin Ragon, Ph.D., Timber Piling Council
108 | ISSUE 3 2021 www.piledrivers.org
/www.piledrivers.org
