TM 5-852-4/AFM 88-19, Chap. 4
ture foundation. Changes in the thermal regime in turn
efforts will normally cause some change in the position of
produce corresponding changes in such factors as the
the permafrost table, even though a continuously
strength and creep properties of the foundation media
degrading condition may not be produced. In borderline
and subsurface drainage. These factors are of far
permafrost areas it may be necessary to use vegetation,
greater importance to foundation stability in the marginal
reflective paint, or shading devices to assist in obtaining
areas of relatively warm, discontinuous permafrost than
a stable permafrost condition for the new construction.
in the areas of either cold, continuous permafrost or of
(6) Serious difficulties may also occur if
deep seasonal frost.
facilities in permafrost areas designed for no heat or a
(2) In both seasonal frost and permafrost
relatively low heating level are converted to higher
areas, heat flow should also be considered in relation to
heating temperatures; the results may be degradation of
discomfort. from cool floors, the cost in added fuel
permafrost and foundation settlement. During design the
requirements of undue heat loss, and the possible
possibility of future higher heating temperatures in
desirability of some heat loss to assist in protecting
facilities must be examined; if there is substantial
against frost heave of footings.
probability of such future conversion, design for the
(3) Large
heat-producing
structures,
higher temperature levels should be seriously
particularly steam and power plants, present an
considered.
especially serious foundation design problem because of
(7) POL and water tanks should have
the potential large and continuous flow of heat to the
ventilated foundations when located on permafrost
foundation. Heavy floor loadings often associated with
subject to settlement on thaw. Water storage tanks are
such facilities may make it expensive to provide
always kept above freezing and if placed directly on the
ventilation beneath the floor. The problem is commonly
ground, would cause continuous heat input into a frozen
further complicated when severe dynamic loadings
foundation even though insulated. POL may be loaded
occur, such as from generator equipment. In addition,
into storage tanks at relatively elevated temperatures,
proper operation of such a plant may be seriously
giving off considerable heat while cooling; also heavy oils
impaired by any differential floor movements. For these
may have to be heated for pumping.
reasons, such structures should, whenever possible, be
(8) In
pile
foundations
the
piles
located on non-frost-susceptible granular soils in which
themselves are also potential conductors of heat from
effects of thawing or frost action will not be detrimental
the building or from warm air or sunlight to which they
(making sure that the granular soil is not simply a
are exposed in the summer into the foundation but this is
relatively shallow layer covering fine-grained soils
seldom a real problem because most conducted heat is
containing ground ice). At heat producing facilities it is
diffused from the pile into the air ventilation space in
essential to make specific provisions for disposal of
winter or into the annual freeze and thaw zone, within a
warm water waste so that degradation of permafrost will
distance of 2 or 3 diameters along the pile. Probing and
not be caused by discharge of such water under or
test pitting have shown slightly deeper summer thaw
adjacent to the foundation. Care must be taken to avoid
directly adjacent to unpainted steel piles which are
leakage from water or steam distribution lines and of
exposed above ground to heating by both direct sunlight
deflection against the ground of warm air from facility
and air, but the amount has not been found to exceed
ventilating systems. Whenever possible, heat producing
about 12 to 18 inches in depth for piles properly installed
plants should be housed in independently located
and is generally much less. However, even this effect
buildings if they might be sources of differential thawing
can be minimized with skirting, white paint or radiation
and subsidence for connected or closely adjacent
shields where needed as discussed in f below.
facilities.
(9) Care should be taken in designing
(4) Thermal stability and potential frost
foundations for refrigerated warehouses, refrigerated fuel
action in foundations of unheated facilities such as
tanks or similar foundations to avoid frost heave from
bridge piers, storage igloos, tower footings, loading
progressive freezing of underlying soils. Such effects
platforms, and exterior shelter areas must also be
may take years to become evident. It should be noted
analyzed carefully. In seasonal frost areas absence of
that insulation only slows such effects; it does not
an artificial heat source in an unheated facility, combined
prevent them.
in some facilities with the shading effect of the upper
(10) Detailed procedures for foundation
parts of the structure, will usually result in maximum
thermal computations are presented in TM 5-852-6/AFM
14
88-19, Chapter 6 .
potential frost penetration, maximum frost adhesion to
b. Estimation of ordinary freeze and thaw
the foundation, and maximum tendency toward frost
penetration.
heave. In permafrost areas, on the other hand, thermal
stability of the permafrost is much easier to achieve in
(1) Design depth of frost penetration.
foundations of unheated than heated facilities.
(a) In areas of seasonal frost
(5) The designer must keep in mind that
conditions, the
disturbance of the natural ground surface by construction
4-7
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