February 25, 2019. Over the following 4.5-month period,
1847 piles were installed.
The secant piles were located using a guide wall—a plain
concrete template cast in a trench. Pile locations were set in the
template using removeable, preassembled steel formwork (Fig. 4).
In addition to helping define the verticality and top elevation of
the secant piles, the template served as a removable form that
exposed the upper reaches of the piles and allowed them to
extend into the subsequently placed seawall/bulkhead pile cap.
The secant-pile construction sequence involved drilling and
placing secondary piles (piles reinforced with only a single GFRP
bar) on Day 1 and Day 2 of a 3-day rotating cycle. On Day 3,
primary piles (those reinforced with 25 No. 8 GFRP bars, spiral
hoops, toe-assembly, and ties) were drilled and placed. This
placement sequence resulted in an interlocked and relatively
homogeneous deep foundation wall-type system (shown in Fig. 5).
Additionally, due to the fact that primary piles (piles with the full
reinforcing GFRP bar cages) are cut into the secondary piles
(those with only a single, central GFRP bar), all the reinforcing
GFRP cages are provided with full cover.
GFRP cage installation
The lightweight, flexible GFRP reinforcing cages in the
primary piles allowed for smooth and rapid installation (Fig. 6).
28 SEPTEMBER 2019 | Ci | www.concreteinternational.com
Due to the relatively loose nature of the Flagler Beach “beach
sand,” the piles were installed using the cased auger-cast
method. The secant-pile and pile-cap installations were also
closely monitored and timed. Based on current estimates, in
comparison with similar projects comprising steel reinforcing
bar cages, the GFRP cages resulted in bar placement time
savings of 32 to 52% throughout the typical observation time of
an extended workweek. More time savings were noted toward
the end of each week.
Figure 7 shows the installed secant piles, continuous pile-cap
construction, and dune reestablishment over the constructed
secant-pile seawall. The reestablished dune will minimize the
environmental and aesthetic impacts of the protective structure.
Summary and Discussion
The SR A1A seawall project comprises GFRP reinforcing
bars in its 1847 secant piles and continuous cap. The GFRP
bars have a high tensile strength (about twice the strength of
steel bars), low weight (about one quarter the weight of steel
bars), and are noncorrosive. As a result of these features, the
cage installations were smooth and rapid, and maintenance
and repair costs over the life cycle of the seawall are expected
to be minimal. While periodic restoration of the dune may be
needed to minimize the potential for scouring of the seawall,
the durable materials in the wall will provide an extended time
window for restoration activities.
Fig. 4: Construction of the guide wall, a concrete template that was used to align and locate the seawall’s secant piles and provide positional
restraint and the required verticality of the piles. The guide wall was removed prior to construction of the pile cap
Fig. 5: The piles were placed in a sequence that ensured that the primary piles could be drilled into and interlocked with the secondary piles