March/April 2022 - 18

was carefully set on the awaiting composite piles at the site,
and capped with a composite concrete slab, which was then
topped off with hardscape or landscaping for the hundreds of
plant and tree species that form the park above.
Soil and Design Considerations
Complex subsurface conditions include soft compressible
clays overlying glacial sands and till, with deep steeply
sloping bedrock underneath that greatly
affected pile axial and lateral capacity.
As the geotechnical/marine engineer,
MRCE performed a subsurface investigation
that included test borings,
laboratory testing, crosshole seismic
testing, lateral load testing and pile
driving analysis (PDA) testing. The
relatively weak subsurface profile
combined with heavy superstructure
mass supported by slender foundations
resulted in large seismic loading when
following NYC Building Code requirements.
Site-specific crosshole seismic
testing allowed for a reduction to the codified seismic
demand. The lateral load testing provided the soil/structure
interaction information (varying spring supports along pile
length) required for analysis by the structural engineers.
To create the undulating landscape surface, the unique pile
design involved long piles that varied extremely in length from
112 to 260 ft (37 to 79 m). An indicator pile program was
performed to help determine pile lengths across the site. Pile
driving was performed with fixed leads and a 270,000 ft-lb
hydraulic hammer. PDA testing was performed at select piles to
confirm axial capacity. While the majority of the piles are
supported directly on bedrock, the piles at the southwest
corner, the last to be driven for this
project, ended up with pile tips in the
glacial till. These piles had extremely
low end of initial drive PDA capacity,
requiring a 40-day restrike before
achieving the required axial capacity.
Pile cut-off was performed using a 48 in
(122 cm) diameter diamond wire saw
machine that produced an elevation tolerance
of within 0.5 in (1.27 cm) and a
smoothness tolerance of 0.25 in (.635 cm).
The design also required pile
Soil profile at pier site
development as a hybrid pile, with an
upper precast, prestressed concrete
section of varying length connected to a lower steel
" stinger " section of varying length. The concrete sections of
the piles were bed-cast by Coastal Precast Systems.
Fabrication was somewhat unique in that it incorporated
18 * DEEP FOUNDATIONS * MAR/APR 2022

March/April 2022

Table of Contents for the Digital Edition of March/April 2022

TOC
March/April 2022 - Intro
March/April 2022 - 1
March/April 2022 - 2
March/April 2022 - TOC
March/April 2022 - 4
March/April 2022 - 5
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