November/December 2021 - 80

Left: System's a cooling tube (yellow oval) and inner temperature measurement location (red circle), and the flow of cooling water into a shaft and bottom of access tube
(solid arrow), and water exit direction (dotted arrow). Right: The contractor's cooling system running
To control temperatures within the
shafts due to hydrating concrete, the
contractor's open system consisted of
six steel access tubes in a 2 ft (0.6 m)
diameter circle within the center of a
shaft; PVC pipes were inserted to the
bot tom of the steel tubes after
concreting was complete. The PVC
pipes conveyed water, pumped from
the adjacent river, from the bottom of
the steel tubes to the top of shaft for
approximately the first two days after
shaft construction. Over the course of
the eight months (August 2019 through
April 2020) it took to construct the
drilled shafts, raw river water used for
cooling varied in temperature from
50°F to 85°F (10°C to 30°C). Within the
saltwater river, there are semidiurnal
tide swings (two high and two low
swings per day) that are roughly equal,
and approximately 7 ft (2.1 m).
Nine interior bents of the new bridge
are supported on a total of eighteen, 8 ft,
2 in (2.5 m) diameter drilled shafts. A test
shaft with a single-level, bidirectional
load cell was also constructed prior to
constructing the production shafts. The
upper roughly 50 to 60 ft (15 to 18 m) of
the shafts included a permanent steel
casing extending through the river and
overburden, which consists of soft
marsh clay and loose sands. The casing
terminates within the Hawthorn Marl, a
silty/clayey sand with N-values of
approximately 4 to 9. The shaft
80 * DEEP FOUNDATIONS * NOV/DEC 2021
diameters reduce by about 4 in (10 cm)
below the casing and are socketed
within the Cooper Marl group, a sandy
silt/clay with N-values of approximately
8 to 20. Concrete was placed via tremie
through polymer slurry.
Temperature Capture
Methods
Crosshole sonic logging (CSL) was used
as the primary assessment of shaft
integrity; therefore, eight 2 in (5.1 cm)
diameter steel tubes were t ied
longitudinally around each 6 ft, 10 in
(2.1 m) diameter drilled shaft reinforcing
cage to allow for CSL probe access.
To determine if the contractor's
cooling system was limiting maximum
temperature and temperature differential
to within project limits,
SCDOT contracted with S&ME to install,
monitor and analyze
Thermal Wires from
Pile Dynamics. The
thermal wires were
u s e d t o o b t a i n
temperatures within
the 19 shafts, after
being either embedded
into the concrete,
suspended within
the water-filled steel
access tubes, or both.
To acquire temperatures
nearer the
center of the shafts,
an additional longitudinal access tube
was tied to the cooling system struts at
about 2.5 ft (0.8 m) from the shaft center,
where the design-build team predicted
maximum temperatures would occur.
Regardless of whether thermal wires
were permanently embedded or
temporarily hung within the steel tubes,
eight wires were generally inserted
around each shaft's perimeter to
measure temperature of the concrete
near the shaft exterior, and one wire was
placed within the shaft interior in an
attempt to measure the maximum
temperature. The temperature gradient
was determined by compar ing
temperatures of the wire at the interior
to those at the perimeter of the shafts.
Therefore, the interior wire location was
referred to as the gradient location.
Typical bell-shaped temperature distribution across a shaft

November/December 2021

Table of Contents for the Digital Edition of November/December 2021