TM 5-852-4/AFM 88-19, Chap. 4
protect concrete by comparatively low temperature
can readily be determined at the time of removal.
heating grids within the insulated form or by the direct
Careful records should be kept of all such temporary fills
burial of heating cables within the concrete. The cables
which must be removed before backfilling operations are
are cut off after the concrete has cured. Heating tapes
resumed. A checklist should be maintained to insure
controlled by a rheostat are particularly useful at exposed
that all temporary fills are removed at the beginning of
corners, tops of walls and other thin sections which are
the following construction sequence.
After such
susceptible to rapid cooling.
insulating temporary fills are removed, the density of the
(3) Ordinary light bulbs are often utilized to
underlying compacted fill should be checked carefully
provide some heat in addition to their prime use as a
before backfilling operations are resumed.
Any
source of light. Since both safety and worker efficiency
previously compacted backfill which has lost its specified
are directly related to illumination, it is imperative that
density due to freezing should be removed or
sufficient lighting be provided. This is especially true in
recompacted.
winter when sunshine is at a minimum and if the
f.
Foundation protection. The need to protect
enclosure further reduces any natural lighting. On small
construction jobs five to ten 100-watt bulbs are sufficient
the foundation against frost heave or thaw settlement
2
illumination for 1000 ft of area.
during construction is sometimes overlooked'". When
d. Fire hazards. Fire is a major hazard in
frost-susceptible soils are present, it is essential that the
arctic and subarctic construction. The use of temporary
foundation be protected until the backfill is in place and,
heaters within an often-confined work area enclosed with
if heat in the structure is depended upon to prevent frost
or containing many combustible materials can be a
action, until heat is available. Methods which may be
potential fire danger. Heating equipment should be
used to provide protection of foundations against frost
maintained and continually inspected to ensure proper
heave in seasonal frost areas include the following,
functioning. Heating units should be carefully positioned
individually or in combinations, as appropriate:
away from formwork, tarpaulins and other combustibles
Cover of earth, hay, sawdust, peat or other
and securely mounted or placed. Electrical heating is
indigenous material.
often advantageous on small jobs because of easy
Directly applied bat, blanket or foam
automated control and greater fire safety, even though
insulation.
cost may be greater. Non-combustible materials should
Insulated structural enclosure or tentage.
be selected where feasible. Tarpaulins should be flame-
Cover of polyethylene sheeting or special
proofed and secured from heavy winds. Firefighting
fabric inflated by hot air blower.
equipment should be strategically placed both inside and
Saturation of foundation soils with salt
outside of the enclosure and building at all times for
solution to prevent freezing.
quick access. When insulation can be used to avoid or
Flooding of foundation with water to a depth
reduce heating requirements, it may be possible to
of a foot or more greater than the normal ice
reduce risk of fire.
thickness for the area.
e. Protection
of
fills,
backfill
and
Hot air, steam, or electrical heat.
embankments. Winter protection of fills, backfills and
Methods to prevent or minimize degradation
of permafrost have been discussed in previous sections
embankments is usually only justified for such purposes
and include: Scheduling work in periods of below
as (a) temporary prevention of freezing pending
freezing air temperatures.
foundation or other emplacement or (b) protection of
Covering permafrost with protective fill or
underlying construction such as utility pipes when
backfill.
construction is incomplete. A covering of peat or loose
Shading or enclosure.
earth is ordinarily the best means of protecting the
Insulation.
backfill from freezing. Loose rock backfill is ordinarily too
Artificial refrigeration.
porous to provide much protection against freezing. If
loose earth is used, building paper, straw, or some other
easily identifiable material can be placed on top of the
compacted backfill so that the limits of the temporary fill
6-12
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