September/October 2023 - 108

FRP Foundation Build-Up
The FRP shapes that, when configured,
make up the FRP foundation are
manufactured by layering of structural
fiberglass fabrics that are in turn
infused with a vinyl ester polymer.
These shapes are designed to have
similar strength and load resistance as
comparable steel shapes. Of note, the
shapes have anisotropic properties due
to the orientation of the fiberglass
fabric strands. Thus, when analyzing
and designing the shapes, it is critical to
account for the direction of the
anticipated load application. After each
individual shape is manufactured, the
shapes are fitted to produce the FRP
deep foundation.
The box stiffeners provide rigidity
to the central pipe section of the FRP
founda t i on. The geome t ry and
placement of the box stiffeners create a
structural assembly with a flexural
rigidity comparable to that of a
foundat ion constructed of steel
products. The addition of the box
stiffeners increases the flexural
rigidity of the pipe, typically by a
minimum factor of about 2 or greater
depending on the design.
A transitional piece provides a rigid
connection designed to resist dynamic
loading created by transient loading
from the transmission line and pole. It
also expedites construction as it
provides a connection point where the
pole can be installed directly onto the
foundation without additional features.
Full-Scale Field Tests
The full-scale FRP foundation load tests
were conducted in Green Cove Springs,
Florida, from November 2021 through
the spring of 2022. The tests assessed
axial, torsional and lateral load
capacities. The test pile was composed
of a FRP 36 in (915 mm) diameter pipe
pile with four box stiffeners oriented at
90 degrees around the pile. The head of
the pile was made of steel and consists
of a sleeve connecting the FRP pile to
the steel pile head, a cap plate welded
on top of the sleeve, and 16 gussets
108 * DEEP FOUNDATIONS * SEPT/OCT 2023
bottom of the foundation to determine
stress levels in the wall of the pipe
section of the foundation. The strain
gauges were protected against damage
during installation and subsequent
foundation removal by an angle cap
fastened to the pipe wall. Data from the
strain gauges were conditioned and
collected at each load increment using
four HBM Quantum X data acquisition
systems (DAQ) and a laptop computer.
The initial phase of the field testing
Detailed pile configuration
reinforcing the connection between the
cap and sleeve. The pile was 36 ft (11 m)
long and 3 ft (1 m) in outside diameter,
with a wall thickness of 1.25 in (32 mm).
The four box stiffeners, attached to the
outside of the pipe pile for added
strength and more contact area, were
basically 1 ft (0.3 m) wide by 1 ft (0.3 m)
deep and ran 27 ft (8m) at the mid height
of the foundation. The box stiffeners
were 1.25 in (32 mm) thick. The pile was
embedded 33 ft (10 m) below the ground
surface for each test. Since in each test
the pile itself would not be loaded to a
yield state, the pile was extracted and
reinstalled at a remote location so that
each test was conducted at an undisturbed
location.
The surface instrumentation included
dial gauges and linear variable
transducers mounted on an instrumentation
panel that was
isolated from the foundation
thus providing a
secure reference frame
for the measurements.
Strain gauges were
mounted on the interior
of the foundation directly
in plan with the
front and back box
stiffeners and at 45 degrees
to the front/back
orientation of the pile at
2 ft (0.6 m) intervals in
depths from the top to
included a subsurface investigation
consisting of cone penetration testing
(CPT), standard penetration testing
(SPT) and undisturbed soil sampling for
laboratory testing to characterize soil
conditions and provide soil design
parameters to facilitate the analytical
design of the test foundations. The CPT
data were used to help identify the
strata of interest for the undisturbed
soil sampling.
Continuous SPT sampling was
conducted between the locations at
which the undisturbed soil samples
were obtained. Sampling was conducted
to end of boring depths of about 65 ft
(20 m). The water level was located
~1.5 ft (0.5 m) below ground surface. The
subsurface investigation encountered
mostly sands to silty sands interbedded
with thin lenses of silt and silty clay
mixtures. Soil consistencies ranged
from loose to dense with lenses of very
stiff material. Tables 1 and 2 summarize
the laboratory test results conducted on
undisturbed samples.
Cone penetrometer field test
September/October 2023

Table of Contents for the Digital Edition of September/October 2023
