September/October 2021 - 117

the tunnel structure. This allowed E.E.
Cruz to accurately model the tunnels
and complete activities required for
installation of a support of excavation
(SOE) within 5 ft (1.5 m) of each tunnel.
The SOE around the North Tube and over
the Middle Tube, respectively, were
designed with rock sockets in very close
proximity to the tunnel structure; the
optimized design permitted expedited
permanent construction from below the
crown of the tunnels, without creating
unbalanced conditions.
Multiple drill rigs in operation
The base design, as per the geotechnical
report and supplemental
historical site investigations, assumed
rock at a lower elevation and allowing
the casing tip to be seated into bedrock
below the influence line of the tunnel.
Rock across the site varied significantly
in its depth from grade between 10 ft
(3 m) to 150 ft (45.7 m), presenting
difficulties when the top-of-rock
elevation varied greatly and caused the
tip of casing to be above the influence
line. Based upon field investigations to
locate the tunnel and other conditions,
it was noted that the actual elevations
of the rock were higher than originally
anticipated. As a result, from analysis of
conditions encountered, the foundation
contractor proposed an alternate design
utilizing an isolation casing to transfer
the loads below the tunnel structure.
This involved extending the rock
sockets below the influence line and
prefabricating the isolation casings
onto the shaft reinforcement for the
upper portion of the shafts.
Foundation Construction
The project schedule required the
construction of 183 permanent shafts
within 9 months. The permanent shafts
ranged from 10 ft (3 m) to 150 ft (45.7 m)
in depth to competent rock, and possessed
diameters varying from 30 in
(762 mm) to 72 in (1,828 mm). To meet
this requirement, E.E. Cruz and its
subcontractor, Underpinning and
Foundation, had seven drill rigs and two
support cranes working simultaneously.
Concrete placement for on-site marshaling area
Various drilling methods were used
to meet strict schedule constraints that
posed challenges for the expansion. One
such challenge was maintaining access
to the existing Javits Center and its air
handling units (AHUs), given that the
design included multiple drilled shafts
at the entrance ramps and under these
AHUs. Posing an additional threat to the
drilled shaft construction activities was
the 1-week time frame to execute the
operations - during the week of
December 25, 2017, to January 1, 2018.
As such, the foundation contractor relocated
AHUs for the drilled shaft installations,
and designed and built high
DEEP FOUNDATIONS * SEPT/OCT 2021 * 117

September/October 2021

Table of Contents for the Digital Edition of September/October 2021

Table of Contents
September/October 2021 - Intro
September/October 2021 - 1
September/October 2021 - 2
September/October 2021 - Table of Contents
September/October 2021 - 4
September/October 2021 - 5
September/October 2021 - 6
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