March/April 2024 - 94

Typical secant pile construction equipment
IPS/EQ Basin Construction
The contractor employed numerous
key steps and methods to construct the
IPS/EQ basin including a sacrificial test
section of three overlapping piles without
reinforcement to verify drilling and
cleanout methods, verticality control,
and tremie concrete placement methods;
and construction of a surface guide
wall to fix the alignment of the tops of
the 4 ft (0.6 m) diameter secant piles.
Drilling and pouring cast-in-place
secant piles took place in a staggered
order so that there were at least two
unreinforced primary pile spaces
between fresh primary pile locations.
Secondary piles, which were reinforced
with W36x135 beams, were typically
drilled after the adjacent primary piles
had set for two to five days. Drilling was
performed with a Liebherr LB36 rig.
Typically, each pile required four to five
hours to drill, but logistics limited
drilling production to an average of one
pile per day. The cased holes were left
filled with fluid overnight. The next
day, typically 10-15 ft (3-4.5 m) of
sediment-concentrated slurry was
removed from within the casing by
pumping from the bottom while clean
water was added to the top of the casing
to maintain a fluid balance. Use of
drilling polymers were attempted to
speed up the sedimentation time, but
94 * DEEP FOUNDATIONS * MAR/APR 2024
Secondary piles, which were reinforced with W36x135
beams, were typically drilled after the adjacent primary
piles had set for two to five days.
they were not effective enough (and
drilling time was not fast enough) to
allow drilling and concrete placement
in the same shift. Four tanks were used
to manage drilling slurry. Next, each
hole was surveyed by Sonic Caliper to
verify verticality and the 5,000 psi (34.5
MPa) concrete was placed by tremie.
Typically, the work was planned so two
piles could be poured in one day shift.
On secondary piles, a 3-4 ft (0.9-1.2 m)
depth of concrete was placed in the
bottom of the casing prior to setting the
wi de f l ange beam. The Le f fe r
VRM150KL oscillator was able to work
independently of the drill crane to
remove sections of casing during the
concrete pours, allowing simultaneous
drilling and pouring operations.
Completion of the 104 secant piles in
the ring took three and a half months.
A reinforced concrete ring beam
was cast onto the tops of the secant
piles to provide additional rigidity at the
tops of the shaft and support a variety of
interior structures within the IPS/EQ
basin including influent pumps,
screenings and odor control. The ring
beam was poured and allowed to reach
a minimum strength before excavation
of the shaft interior began.
To comply with the no-dewatering
requirement, the contractor excavated
the interior of the secant pile ring with
two operations. First, the unsaturated
surface soils and whatever could be
reached with the boom of a Caterpillar
335F excavator were excavated to a
depth of 15-20 ft (4.5-6 m). Next, a
dredge pump was affixed to 120 ft (37 m)
long pile driving leads that were moved
around the shaft interior. Dredged
material ran through a nearby sedimentation
operation, with the " cleaned "
water pumped back into the shaft interior.
Dredging of approximately 18,000 cu
yd (13,760 m3) in situ below the water
table took approximately three weeks.
Prior to placing the tremie concrete
base plug, the secant pile walls were
scrubbed by jetting through the dredge
and making several passes with a
concrete-filled, rebar-encrusted
" toothbrush. " Approximately one week
was spent fine grading the excavation
bottom and cleaning the walls.
March/April 2024

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