TM 5-852-4/AFM 88-19, Chap. 4
c. Pile emplacement methods. Many of the
ference between the exposed top and the embedded
145
bottom of the pile in winter .
earlier foundations in permafrost used local timber,
(d) Both the above systems are self-
installed in steam or water-thawed holes to depths which
initiating systems. They automatically cease operation
rarely exceeded 20 feet. Normally the piles were pushed
when air temperatures become warmer than those
or lightly driven into the pre-thawed holes. They often
around the lower part of the pile. They are intended to
required restraint to prevent flotation. Pile length and
require no operating attention once properly installed.
spacing tended to be dictated by structural requirements
Patents have been obtained for proprietary systems in
of the building rather than by pile bearing capacity or by
both areas.
the ability of the permafrost to accept the heat introduced
(e) In a fluid forced circulation
during the installation. Pile installation techniques now
utilize modern drilling or driving techniques and
system, analogous to a circulated hot water heating
effectively minimize permafrost thermal disturbance.
system, a pump is used to circulate a nonfreezing liquid
Installation methods are determined by ground
or gas through the pile and through a surface heat
temperatures, the type of soil, the required depth of
exchanger exposed to the atmosphere in winter, or
embedment, the type of pile, and the difficulty and cost of
through a mechanically refrigerated heat exchanger
mobilizing the required equipment and personnel at the
without regard to season. The refrigerated fluid is
site. Installation methods which may be considered are
usually introduced at the bottom of the pile through a
as follows: (1) Installation in dry augered holes.
central inner pipe and then flows upward in contact with
(a) Holes for the piles may be drilled
the inner wall of the pile. The same objective may be
in permafrost by using earth augers with bits specially
gained by circulation of refrigerated fluid through tubing
37,74,80,133,211
.
Two-feet-
designed for frozen ground
attached to the exterior of the pile for artificial freezeback
diameter holes can be advanced at rates up to about I
as described in d (3) below. The refrigeration may be
ft/min in frozen silt or clay depending on type of bit,
temporary for the purpose of achieving initial freezeback
ground temperature and size of equipment. Holes up to
during construction or may be permanent where required
4 feet or more in diameter can be drilled readily in such
by the design thermal conditions. Direct circulation of
soil. Advantages include minimum required effort and
cold winter air through a pipe pile by a simple fan has
equipment, accurate positioning and alignment, and
been shown to be very effective in principle", but it is
accurate control of hole dimensions and therefore of
possible the circulation may be rapidly blocked by frost
heat input into the permafrost. Drilling is easily carried
accumulation if the system is under unfavorable
out under winter conditions when the frozen ground
conditions; this alternative is therefore not recommended
surface permits ready mobility, without the problems of
for permanent construction in the present state-of-the-
handling water or steam under freezing air temperatures.
art.
(f) Thermal piles which depend on
However, the method is not likely to be feasible in
coarse, bouldery frozen soils. The holes may be drilled
seasonal dissipation of heat to the cold winter air may be
undersize and wood or pipe piles may be driven into the
expected to show a temperature drop effect to about 8 to
holes. However, more commonly the holes are drilled
10 feet radius by the time above-freezing air
oversize and soil-water slurry is placed in the annular
temperatures arrive in the spring. At least a small
space around the pile and allowed to freeze back as
depression of ground temperature should remain
described below.
through the fall from this effect, in order for the piles to
(b) The mixture of soil and water
achieve their long range purpose. Piles which use
(slurry) used to fill the annulus between augered hole
artificial refrigeration can keep the ground refrigerated in
and pile can often transfer the imposed pile loads to the
all seasons.
(g) An essential requirement of all
surrounding frozen soil more effectively than the original
in-situ soils. The auger-slurry method is easily adapted
closed system thermal piles is freedom from leakage.
to production methods the auger followed by a pile-
Leakage of liquid containing antifreeze may seriously
placing crane, followed by a slurry crew. If surface water
and permanently degrade the ad freeze bond strength of
is not entering the augered holes which would require
the pile. Leakage of gas through fittings, welds or
relatively quick action, they may be covered with
porous metal may quickly make the system inoperative.
plywood, or by other methods, until pile placement is
All such installations must therefore be very carefully
convenient.
This will permit each crew to work
pressure tested to detect any leakage. All thermal pile
independently. Silt from borrow or from the pile hole
units using liquefied petroleum products must be
excavation can be used for the slurry, as well as gravelly
constructed to meet the standards of the National Fire
sand, sand or silty
Protection Association NFPA 58-1979 Standard for the
Storage and Handling of Liquefied Petroleum Gases and
the ASME Section VIII-1977 Pressure Vessels Division
1. Methods of computing heat transfer by thermal piles
are presented in e below.
4-112
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