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Chapter 2
Helical Foundation Systems
CHAPTER 2
HELICAL FOUNDATION SYSTEMS
2.4 Benefits
The use of helical piles in construction continues
to increase due to product and equipment
versatility and the various benefits that the
systems offer. Some of the benefits/advantages
of helical piles include:
•
High capacity deep foundation alternative
–
Allowable torque-rated capacities on the order
of 60 kips may be achieved with helical shaft
sizes up to 3.5 inches in diameter, as noted in
ICC-ES AC358 for conforming products. Even
higher capacities may be achieved with larger
shaft sections.
•
Predictable capacity
– With adequate
soil information and designer experience,
system capacities may be estimated very
closely to capacities determined from full-
scale load testing.
•
Lead sections and extensions can be
configured to achieve design depth and
capacity
– The design professional will
choose the helical pile shaft size and helix
plate configuration appropriate for the soil
conditions. Additional helix plates may be
considered on extensions when bearing in
weaker soils. Special “V-style” plates are
available to assist in penetrating dense soils.
•
Well-established torque to capacity
relationship
– Empirical torque factors
have been established through years of
product testing. Default capacity to torque
ratios are listed in ICC-ES AC358 for
conforming products.
•
All-weather installation
– Helical piles can
be installed through inclement weather and
freezing temperatures.
•
Installed in areas of limited or tight access
– Helical piles can be installed with hand-
held equipment, mini-excavators, skid steers,
backhoes and larger track equipment
(Figures
2.4.a1, 2.4.a2 and 2.4.a3)
. The equipment and
drive heads can be sized according to the
project design loads as well as site access.
•
Low mobilization costs
– Helical piles have
in part become a popular deep foundation
option because of the ability to achieve
moderate to high capacities, yet be installed
with smaller equipment. Mobilization costs are
then much lower than other deep foundation
alternatives, which in turn makes helical piles
an economical solution for many projects.
Figure 2.4.a1
Skid steer installing helical
piles within limited space at a substation
Figure 2.4.a2
Mini-excavator lowered by
crane into excavation to install helical tiebacks
Figure 2.4.a3
Helical piles installed with hand-held
equipment to support new elevator within existing school