TM 5-852-4/AFM 88-19, Chap. 4
degree of stability, with respect to frost heave or thaw
account in design and measures taken as necessary to
settlement, as the main or heated parts of the structures.
avoid detrimental effects from either the structural
k. Control of settlements which may result
stresses developed by the frost forces or from the
from thaw.
resulting deformations.
Thaw penetration beneath a slab or
(1) In the case of slab or footing
foundation readily occurs non-uniformly. The resulting
foundations the heaving thrust of underlying frost-
differential stresses and strains may cause distortion and
susceptible soils may act directly upward against the
cracking in the slab, foundation and structure. If thaw is
base of the foundation as illustrated in figure 4-42a or
rapid and imposed loadings are high, displacement of
laterally against foundation walls as in figure 4-42b.
over-stressed, thaw-weakened foundation soil is
Piers, posts, piles, or entire foundations surrounded by
possible. Under dynamic loading, pumping and mud
frost-susceptible soils are also subject to frost heaving
boils are possible. Thaw water may emerge upward.
as the ground adjacent to lateral surfaces is displaced
These thaw settlement problems should be avoided by
annually as shown in figure 4-42c. Should the soil
adopting the proper foundation design approach for the
conditions, moisture availability, loading or frost
conditions and by designing for full thermal stability
penetration vary under the foundation the frost heaving
control, using the principles presented in paragraphs 4-1
effects will be non-uniform. to illustrate the problems
and 4-2. If damaging thaw settlements should start to
involved, figure 4-43 shows the heave of floor slabs in
occur, a mechanical refrigeration system may have to be
wing hangars at Loring AFB, Maine".
Through a
installed in the foundation or a continual program of
combination of sufficient clearance of the slab around
jacking and shimming will have to be adopted together
the interior columns and sufficient anchorage of the
with installation of flexible utility connections.
I.
Control of frost heave and frost thrust.
column footings, no movement of the
When estimation of the depth of seasonal frost
penetration and evaluation of frost uplift or thrust forces
indicate potential problems, they must be taken fully into
Figure 4-42a. Frost Action Effects (Heaving of soil in seasonal frost zone causing direct upward thrust on overlying
structural elements.)
Figure 4-42b. Frost Action Effects (Freezing of frost-susceptible soil behind walls causing thrust perpendicular to freezing
front.)
4-66
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