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.