November/December 2021 - 82

by soil, temperature versus depth plots
were used to evaluate the effects of the
cooling system. Above the mudline,
temperature versus depth plots were
used to determine if the flowing river
influenced the shaft's temperature
rather than the cooling system.
At the time of peak temperature (16
hours, in the left-most plot), the gradient
wire was almost always hotter along the
shaft length than the perimeter wires.
Above the mudline, the perimeter wires
had much lower temperatures of about
115°F (46 °C), as compared to temperatures
of about 135°F (57 °C) than the
perimeter wires below the mudline,
indicating the river was cooling the
perimeter of the shaft exterior more
efficiently than the cooling system
alone. However, the gradient wire
showed a relatively homogenous
temperature at 16 hours, indicating the
shaft's interior wasn't influenced by
river cooling. This was true for most of
the shafts on this project when the
largest temperature differential across
the shaft (calculated by comparing the
gradient wire and the coolest perimeter
wire) was observed above the mudline
near the peak temperature. Therefore, a
relatively cool water source on the
exterior of shaft can have the unintended
consequence of exacerbating the
temperature differential. Without the
cooling system, it can be inferred that
temperatures in the interior of the shaft
would have been greater, producing an
even larger temperature differential
above the mudline.
At about 49 hours, around when the
cooling system was shut off, the
gradient wire above the mudline was
hotter than the perimeter wires, but the
river temperature impacted the
perimeter and shaft interior. The
impact of the river was indicated by the
decreased temperature compared to
those below the mudline, and was
greater in the perimeter wires. Below
the mudline, the gradient wire was
cooler than perimeter wires, indicating
the cooling system's greater efficiency
in cooling the shaft center.
82 * DEEP FOUNDATIONS * NOV/DEC 2021
Shaft temperature versus depth was
also evaluated at the end of TIP
monitoring, or almost 6 days after shaft
pouring, and 4 days after turning off the
cooling water. Along the shaft's entire
length, the gradient wire was about 5°F
to 10°F (3°C to 5.5°C) hotter than the
perimeter wires, indicating the entire
shaft cross section at any given depth
was cooling at a similar rate. Above the
mudline, the perimeter wires were
approximately the temperature of the
river. However, the gradient temperature
was warmer, indicating the shaft center
was still not equal in temperature to the
ambient river temperature.
Concrete Placement Consequences -
Most of the drilled shafts were constructed
from floating barge " islands. "
While equipment and personnel could
be placed on the islands, the concrete
had to be delivered to the shaft from the
existing bridge. Additionally, bridge
weight restrictions limited the concrete
trucks to a capacity of 6 cu yd (4.5 cu m),
with up to two trucks simultaneously
offloading concrete. Due to the logistics
required to offload 34 trucks and tremie
the approximately 200 cu yd (150 cu m)
of concrete for a shaft, pours generally
took 5 hours or more.
When the temperature versus depth
of a shaft was reviewed about 7 hours
after the end of concrete placement and
shaft cooling, a trend of increased
temperature from the top to the bottom
of the shaft was observed. This shows
that the older concrete near the bottom
was hydrating, and the concrete near
the middle was starting to hydrate,
while the uppermost concrete had yet
to start hydrating. It is unlikely that
predictions of temperature differentials
in mass concrete consider this
phenomenon with any regularity.
About 11 hours after concrete placement
ended (left plot), when the concrete
was still hydrating aggressively and
creating heat, the perimeter wires
indicated zones of cooler temperatures
between depths of 7 to 18 ft (2 to 5.5 m)
and 65 to 80 ft (20 to 24 m). These temperature
reductions were about 12°F
(7°C) and 30 °F (17 °C) cooler, respectively,
than temperatures elsewhere. This
anomalous zone resulted in an approximately
46 °F (25.5 °C) temperature differential
between the gradient wire and the
Concrete offloading from original bridge for barge-based construction of drilled shafts
November/December 2021

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