TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 4-72. Specific solution of slurry freezeback rate134.
assume the slurry heat to be conducted only in a
be used to accomplish the desired freezing of the
horizontal radial direction. The actual heat paths during
backfill. The artificial freezing may be accomplished by
summer and winter are approximately as shown in figure
circulation of refrigerating fluid through longitudinal or
4-73. However, while freezeback time may be increased
spiral steel or copper tubing attached to the pile, or by
or decreased by deviations of heat flow from the
use of thermal piles as described in e below. Brine or
horizontal, and adjustment of the assumed "effective"
glycol solutions and ambient air have all been used as
temperature of the permafrost may sometimes be
the circulating fluid. However, the use of propane or
necessary to allow for this effect, the increase in
other refrigerants of similar characteristics has been
freezeback time which may be caused by proximity
found to be the most efficient and economical. Propane
between adjacent piles is a more dominant consideration
has the disadvantage of flammability. The refrigerant
((4) below), everything else being equal.
may be circulated through piles either individually or in
(3) Artificial freezeback.
series, using a portable compressor, as shown in figures
(a) When ground temperatures are
4-74 and 4-75. The size of the compressor depends on
the number of piles to be frozen and the amount of heat
too warm or the amount of heat introduced is too great to
to be removed from the slurry. Pipe size, exposure area
accomplish natural freezeback of slurry within the
per foot of pile length, and rate of circulation are other
planned construction period, artificial refrigeration must
4-118
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