November/December 2021 - 81

As concrete cures, cement hydrates
and generates heat, which creates a
time-dependent temperature increase
within a shaft. The peak temperature is
typically defined as the time, where
time zero is the end of the concrete pour,
when the maximum overall average
concrete temperature occurs. Once a
shaft reaches peak temperature, it cools
and eventually returns to equilibrium
with the surrounding environment.
Within drilled shafts without a
At top, shaft cooling system with cooling tubes (blue
circles), thermal wire nodes (red ovals), and gradient
location (large red circle). At bottom, temperatures
across shaft 12 h after shaft cooling began
cooling system, the temperature across
a shaft generally follows a bell-shaped
curve, with the highest temperatures
occurring at the shaft center, and the
lowest, at its exterior where heat
dissipates radially into the surrounding
soil. However, when a cooling system is
added within the shaft, this bellshaped
temperature curve becomes
distorted.
Within the test shaft, thermal
measurements were taken along the
cooling system supports at horizontal
increments of about 6 in (15 cm) across
the shaft interior. Cooling water was not
introduced into the test shaft until
approximately 12 hours after concrete
placement ended. Therefore, initially the
typical bell-shaped temperature distribution
across the shaft diameter was
observed prior to running the cooling
system. However, once cooling water
was introduced, the temperature
distribution immediately changed to a
double-hump shape. The temperatures
nearest the cooling tubes indicated the
lowest temperatures, and the highest
temperature occurred in the proximity
of the gradient measurement tube. This
provided some confidence that highest
temperatures were not expected to occur
at the center of the shaft, but near the
interior wire location, where the calculations
indicated it would be highest
while the cooling system was operational.
Thermal Data
Temperatures Vs. Depth Results - The
thermal wires recorded temperature
data versus depth at 10-minute
intervals, providing the advantage of
near ly cont inuous temperature
readings with time. After reviewing the
recorded temperatures, the time of
peak shaft temperature, end of shaft
cooling and the end of TIP monitoring
were selected as three optimal times to
evaluate the temperature versus depth
trends of the shafts. Elapsed times were
calculated when concrete placement
was complete, which was generally
when shaft cooling was introduced.
Below the mudline at a depth of
approximately 30 ft (9.1 m), which
represents a typical shaft surrounded
Temperature vs. depth for wires suspended in water-filled steel access tubes at peak temperature (left, 16 h); end of shaft cooling (center, 49 h); and end of TIP
monitoring (right, 6 d). Gradient wire is the purple line, average of perimeter wires, black line, and other colored lines, perimeter wires.
DEEP FOUNDATIONS * NOV/DEC 2021 * 81
November/December 2021

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