TM 5-852-4/AFM 88-19, Chap. 4
accurate economic evaluation of optional approaches.
4-3. Control of movement and distortion from freeze
The geometrics, size and loading of the members of the
and thaw.
The foundation design engineer must
foundation will determine the upward heave force and
establish the amounts of movement and distortion which
displacement pattern and adfreeze stresses developed.
may be tolerated in the structure supported by the
The foundation, structure, and loading will react, in turn,
foundation and must develop his design to meet these
to restrict the amounts of actual heave displacement
criteria. Foundation design must interrelate with design
which can occur.
of the structure.
d. Wood frame structures have relatively high
a. Movement and distortion may arise from
flexibility and capability for adjustment to differential
seasonal upward and downward displacements, from
foundation movements. They have often continued to
progressive settlement arising from degradation of
give acceptable service even under conditions of such
permafrost, from horizontal seasonal shrinkage and
severe distortion that doors have required substantial
expansion caused by temperature changes, and from
trimming in order to open and close, window glass has
creep, flow, or sliding of material on slopes. Detrimental
required replacement with plastic film to reduce
effects may consist of the following:
breakage, and floors have become conspicuously
Tilting of floors
unlevel.
Steel frame structures usually are highly
Jamming of doors and windows
suitable for modern military facilities, are highly reliable
Cracks and separations in floors, walls and
and versatile, and offer excellent long term service
ceilings
capability.
They are more rigid than wood frame
Breaking of glass Complete disorientation of
structures but more tolerant of movement than reinforced
structural stresses
concrete and masonry. Both pad supported and fixed
Structural failures
types of foundations may be used for wood and steel
Shearing of utilities within structure, at structure
structures. Concrete and masonry exhibit in the cold
perimeter, and in the ground
regions about the same responses to distortion as in
Damage to installed equipment or interference
temperate or tropic areas. Foundations which provide
with its operation
complete freedom from cracking or distortion of the
b. Small flexible buildings on posts and pads
structure are required for concrete or masonry
can easily tolerate several inches of seasonal movement
structures.
provided the differential between various parts of the
e. If the foundation materials are thaw-stable,
foundation is not excessive and provided utility
clean, non-frost-susceptible granular soil or ice-free
connections have the requisite flexibility. Post and pad,
sound bedrock, the same type of foundations may be
footing and column, and simple pile foundations such as
considered as would be employed in the temperate
illustrated in figures 4-13 through 4-20 are generally
zones.
satisfactory for such relatively light structures. However,
f.
Figure 4-38 shows a typical record of
permanent structures should be designed to be free from
permafrost degradation and vertical movements of a
both seasonal and progressive movements or distortions
small wooden building constructed with a "floating"
during the life of the facility, except for the normal cyclic
foundation consisting of a rigid concrete raft on a gravel
effects caused by seasonal expansion and contraction of
pad. This particular design is not an economical one; it
ground and structural elements. For certain technically
was constructed as an experiment","'. Although regular
complex facilities such as radar or communications
seasonal vertical movements occurred and there was
installations which can tolerate only minute movement,
gradual progressive degradation of permafrost at the
exceptionally stringent foundation stability and response
warmer southwesterly side of the foundation which
requirements may be established.
received maximum sunlight in the summer, resulting in
c. As foundation loadings increase, support
tilting, the building itself performed excellently. warmer
members must be more closely spaced and/or have
southwesterly side of the foundation which received
heavier cross-sections, and footings must have larger
maximum sunlight in the summer, resulting in tilting, the
areas, with less and less space between footings.
building itself performed excellently.
Figures 4-21 through 4-23 show designs of higher load
g. Figure 4-39 shows displacements for a
capacity.
Where these systems may become
small wooden building supported on wood piles
uneconomical, designs such as the systems shown in
embedded in permafrost",'". In this case, 1 of the 20
figures 4-24 through 4-28, capable of very high unit
supporting piles failed to achieve freeze-back in
loadings, should be considered. As a last resort, where
permafrost and continued to heave progressively
even such air ducts cannot be incorporated into the
upward. Distortion of the wooden building of more than 6
foundation, tubing systems through which liquid
inches occurred before the top of the pile was sawed off
refrigerant is circulated may need to be used in the
and a jack in
foundation. The magnitude of the foundation loading will
have an influence on the type of material used, and will
determine the size and arrangement of foundation
components. The relative in-place costs of materials
such as wood, steel and concrete must be known for
4-59
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