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Description / Abstract:
General
Piles are slender structural elements installed in the ground to
support a load or compact the soil. They are made of several
materials or combinations of materials and are installed by impact
driving, jacking, vibrating, jetting, drilling, grouting, or
combinations of these techniques. Piles are difficult to summarize
and classify because there are many types, and new types are still
being developed. This report covers only the types of piles
currently used in North American construction projects. A pile type
can be assigned a wide variety of names or classifications by
various agencies, codes, technical groups, and in various
geographical regions. No attempt is made herein to reconcile the
wide variety of names used with a given pile type.
Piles can be described by the predominant material from which
they are made: steel, concrete (or cement and other materials), or
timber. Composite piles have an upper section of one material and a
lower section of another. Piles made entirely of steel are usually
H-sections or unfilled pipe; however, other steel members can be
used. Timber piles are typically tree trunks that are peeled,
sorted to size, and driven into place. The timber is usually
treated with preservatives, but untreated piles can be used when
positioned entirely below the permanent water table. The design of
steel and timber piles is not considered herein except when used in
conjunction with concrete. Most of the remaining types of existing
piles contain concrete or a cement-based material.
Driven piles are typically top-driven with an impact hammer
activated by air, steam, hydraulic, or diesel mechanisms, although
vibratory drivers are occasionally used. Some piles, such as steel
corrugated shells and thin-wall pipe piles, would be destroyed if
top-driven. For such piles, an internal steel mandrel is inserted
into the pile to receive the blows of the hammer and support the
shell during installation. The pile is driven into the ground with
the mandrel, which is then withdrawn. Driven piles tend to compact
the soil beneath the pile tip.
Several types of piles are installed by drilling or rotating
with downward pressure, instead of driving. Drilled piles usually
involve concrete or grout placement in direct contact with the
soil, which can produce side-friction resistance greater than that
observed for driven piles. On the other hand, because they are
drilled rather than driven, drilled piles do not compact the soil
beneath the pile tip and, in fact, can loosen the soil at the tip.
Post-grouting may be used after installation to densify the soil
under the pile tip.
Concrete piles are classified according to the condition under
which the concrete is cast. Some concrete piles (precast piles) are
cast in a plant before driving, which allows controlled inspection
of all phases of manufacture. Other piles are cast-in-place (CIP),
a term used in this report to designate piles made of concrete
placed into a previouslydriven, enclosed container. Concrete-filled
corrugated shells and closed-end pipe are examples of CIP piles.
Other piles are cast-in-situ (CIS), a term used in this report to
designate concrete cast directly against the earth. Drilled piers
and auger-grout piles are examples of CIS piles.