TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 4-63. Case of isolated square footing (by CRREL)
.
and ground surface
Otherwise the thaw depth should be determined by
Mean annual air temperature
computation using procedures and terminology of TM 5-
(MAT) = 23F.
852-6/AFM 88-19, Chapter 6'".
As indicated in TM 5-852-6YAFM 88-19, Chapter 6 use
Ground temperature below zone
the equation,
of seasonal variations (at 50
X=λ√48KnI
feet, measured) = 27 F.
Design air thawing index, I = 2900
L
Length of thawing season, t = 150
where
days
X
=
depth of thaw, ft
3
Conversion factor for air thawing
L
=
volumetric latent heat of fusion, Btu/ft
λ
index to surface thawing index,
=
a coefficient which takes into
n = 1.0 for building-shaded
consideration the effect of temperature
area (see table 4-1 and TM 5-
changes in the soil mass (other factors
852-6), dimensionless. (Note
are as previously defined)
λ
that this factor does not apply
=
is determined from TM 5-852-6/AFM
for the freezing period or for the
88-19, Chapter 6, figure 13, using
overall annual heat exchange.)
values of α and calculated as
(b) Determining required depth of
follows:
footing. The footing should be founded below the top of
permafrost for stable bearing. To establish this position
Thermal ration α =
V
o
the depth of seasonal thaw must be determined. If
V
s
previous measurements of depth of thaw are available,
these should be used, adjusted if necessary to
correspond with the design air thawing index condition.
4-97
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