September/October 2022 - 103

diameter to determine the most costeffective
option. Various combinations
of pile diameters were considered to
optimize not only the pile costs, but the
pile cap costs as well. To aid in visualizing
the relative compression, tension
and shear requirements across the site,
the team created heatmaps of pile
quantity and per pile loads at each
column location for each diameter.
These heat maps were also helpful in
ensuring that material efficiency did
not come at the cost of production
efficiency. By comparing and combining
heatmaps, the team was able to
develop a column-specific approach
consisting of 12, 16 and 24 in (305, 406
and 610 mm) diameter APG piles that
optimized pile and pile cap costs as well
as production time.
Constant and clear communication
was required between the contractor
and the project engineer of record,
Skidmore, Owings & Merrill, who
maintained design responsibility for
the pile caps, with design assistance
from Berkel engineers. This collaborative
effort resulted in a very robust
foundation redesign process and
streamlined resolution of production
issues such as short refusals.
Monitoring
Due to the range of pile sizes and
lengths, the proposed APG pile system
was planned for installation from
multiple crane-supported, swingingTable
1: Approximate lower levels of soil/rock profile
Approximate Elevation in ft (m)
Above 945 (288)
945-930 (288-283)
930-910 (283-277)
910-900 (277-274)
900-885 (274-270)
Below 885 (270)
Soil Classification
Existing Fill
Native Clay
Weak Shale
Strong Shale
Limestone
Shale with Limestone
Heatmap of 16-in APG
pile quantity per column
lead platforms with the gearbox and
augers tailored to the piles to be
installed by that platform.
The installation platforms were
outfitted with automated monitoring
equipment to measure, calculate and
record specific parameters during pile
installation. Parameters recorded and
calculated at one-second intervals
during pile drilling included: tool
depth and penetration rate, torque
applied to the auger, and the rotation
rate of the auger.
These parameters can be observed
in real-time as piles are being constructed,
either onboard the installation
platform or remotely via wireless
display. This real-time observation is
referred to as monitoring while drilling.
For the subject project, penetration rate
and torque were correlated to the soil
and rock strata of the subsurface profile
during each phase of pile load testing
and used during production installation
as a check to ensure that piles were
installed within the target stratum for
the loads that pile was to support.
Testing, Final Design and
Production
The project team divided the site into
zones represented by micro-localized
models to expedite construction schedule
and optimize production foundation
lengths. The alternate approach
required an extensive load test program
to verify the performance of the range of
proposed diameters in the various
proposed bearing strata; from friction
piles embedded in the overconsolidated
alluvial soils, to piles socketed into
weak shale, and piles installed to
practical refusal on intact limestone.
This program added about $300,000 to
the estimated cost of the approach,
however it resulted in the reduction of
overall pile cost by just under $1 million
in time and materials saved from the
optimized approach.
There was a minimal preproduction
test phase that started with 16 in
(406 mm) diameter piles in the southwest
corner of the project site. As production
pile installation commenced,
additional test piles were installed as
more areas of the site were opened for
construction. The results of each phase
of the program were used to calibrate
the micro-localized zone models to set
final design lengths for each pile type at
each column location within a particular
zone.
DEEP FOUNDATIONS * SEPT/OCT 2022 * 103
September/October 2022

Table of Contents for the Digital Edition of September/October 2022
