TM 5-852-4/AFM 88-19, Chap. 4
contact with it. If a beam supported near the surface is
oriented parallel to the direction in which frost heave
used and the outer edge of the slab is heaved then hinge
acts.
Anchored frost isolation sleeves should be
action will occur at the inner edge, but there will be no
installed if materials are frost-susceptible. When utility
step displacement. In some cases, a layer of insulation
lines enter a facility laterally below ground level as in
under the slab may assist in providing the most
figure 4-97b, they should be placed below the anticipated
economical solution. Another alternative way of allowing
depth of seasonal frost penetration to avoid shear at the
for minor heave is to provide a downward step as small
interface. When backfill is placed under utility lines it of
as 2 to 4 inches with the apron left free to heave.
course must be compacted in accordance with standard
(2) In extreme climates it is considered
provisions to avoid settlement. However, precautions
preferable to hand doors of heated dwellings to open
must be taken to prevent freezing and ice segregation in
inward because of the possibility of blocking of doors by
such fill during placement if the soil will later thaw. It is
heave of exterior aprons, stairs, or platforms, or by heavy
impractical to attempt to estimate the amount of such
snow or ice, even though this is contrary to conventional
frost heaving and to pre-position utility lines in order to
fire safety regulations.
allow for consequent later settlement on thaw.
c. In permafrost areas utility lines most
4-16. Utilidor and pipeline foundations.
commonly run above the ground surface and
Methods of supporting utilidors and pipelines above and
connections into buildings are relatively easily effected,
below ground are discussed in TM 5-852-5/AFM 88-19,
13
although specific provisions to permit relative movement
Chapter 5 . Techniques for design of the pile or other
are often needed. If placement of utility lines below
types of foundation construction and support described
ground is desired in permafrost areas the possibility of
therein should be in accordance with the provisions of
shearing of the lines by relative movement at the
this manual.
foundation wall must be considered. If the utility line is
4-17. Connection of utilities to buildings.
laid within permafrost, the possibility that permafrost
a. The manner and depth at which utilities
degradation and foundation settlement may later occur
(water, sewer, electric, communications, etc.) approach
must be carefully examined. If placement of the utility
and enter building below ground may be a factor in
line in the annual frost zone overlying permafrost is
foundation design. It is important that provisions be
considered, both thaw settlement and frost heave effects
made so that utility lines will not be sheared by heave or
may have to be contended with, depending on the type of
settlement where they pass through foundation walls and
soil. If there is any possibility that such a below-ground
that lines carrying water will not freeze. In purely
utility line may be subject to shearing action at the
seasonal frost areas, water lines 6 inches or less in
foundation line, it must either be laid within a surrounding
diameter should be laid with invert 6 inches below the
conduit of large enough diameter to isolate it from any
computed maximum frost penetration depth. Larger
possible shearing action or it must be brought above the
water pipes should be laid so that the top of the pipe is at
ground outside the foundation and enter the building
the computed maximum frost penetration depth. In
through a conventional above-ground connection.
areas of very deep frost penetration it may be more
4-18. Drainage around structures.
economical, if the soils are non-frost-susceptible, to
a. Considerable permafrost thaw damage can
place the entire system of water pipes at nominal depth
be caused to foundations by seemingly insignificant
and provide continuous circulation and heat during the
amounts of water entering or moving through unfrozen
freezing season; for some situations insulation may also
ground under and near structures. Where groundwater
be used effectively if it is protected against moisture
flow is a potential threat to thermal stability of
absorption. Because of wide variations in operating
foundations, a substantial analysis of groundwater flow
conditions, it is difficult to give a simple rule for
may be required, including possibly the use of dye to
determining the minimum depth of sewer pipes to
trace directions and velocities. In fine-grained soils,
prevent freezing. However, pipes located according to
seepage flow is slow and may amount to only a few
the above criteria for water pipes should nearly always
inches or feet per year, but in coarse gravels flow in the
be safe, as sewage leaving a building is normally
annual thaw zone as high as about 2500 ft/hr has been
appreciably warmer than the water supply entering the
105
measured If such groundwater flow is in contact with a
building. However, when water supply lines are allowed
source of warm water such as a lake or pond, substantial
to waste continuously into sewer lines in extremely cold
disruption of thermal regimes and melting of permafrost
periods to prevent water line freeze-ups, the sewage flow
may result. Water temperatures at the surfaces of
may be abnormally cold. Factors affecting design of
shallow ponds and lakes in permafrost areas have
sewer lines with respect to freezing conditions are
outlined in TM 5-852-5/AFM 88-19, Chapter 5'3 and TM
b. As illustrated in figure 4-97a, utility lines
passing through the seasonal frost zone should be
4-160
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