TM 5-852-4/AFM 88-19, Chap. 4
design depth of seasonal frost penetration for situations
design because permanent buildings and other
not affected by heat from a structure should preferably
structures are less tolerant of vertical movement than
be the maximum found by actual measurement under
pavements. For structures of a temporary nature or
conditions representative of those for the facility design,
otherwise tolerant of some foundation movement, the air
or by computations if measurements are not available.
freezing index for the coldest year in ten or even the
When measurements are available, they will frequently
mean air freezing index may be used, as may be most
need to be adjusted by computations to the equivalent of
applicable.
the freezing index selected as the basis for design, as
(b) For average conditions, the air
measurements may not be available for a winter having
freezing or thawing index can be converted to surface
a severity equivalent to that value. The air freezing index
index by multiplying it by the appropriate n factor from
to be used in the estimate of frost penetration should be
table 4-1.
selected on the basis of the expected life of the structure
(c) The frost penetration can then be
and its type. For average permanent structures, the air
computed using the detailed guidance given in TM 5-
14
852-6/AFM 88-19, Chapter 6 . Approximate values of
freezing index for the coldest year in 30 should be used;
frost penetration may also be estimated from figure 4-4b
this is more conservative than the coldest-year-in-ten (or
for
average of 3 coldest in 30) criterion used for pavement
Table 4-1. n - Factors for Freeze and Thaw (Ratio of Surface Index to Air Index)14
(a)
For Freezing
For Thawing
Type of Surface
Conditions
Conditions
Snow Surface
1.0
-
Portland Cement Concrete
0.75
1.5
Bituminous Pavement
0.7
1.6 to 2+ (b)
Bare Soil
0.7
1.4 to 2+ (b)
Shaded Surface
0.9
1.0
Turf
0.5
0.8
Tree- covered
0.3(c)
0.4
(a)
Surface exposed directly to sun and/or air without any overlying dust, soil, snow or ice, except as noted otherwise,
and with no building heat involved.
(b)
Use lowest value except in extremely high latitudes or at high elevations where a major proportion of summer
(c)
Data from Fairbanks, Alaska, for single season with normal snow cover permitted to accumulate.
4-8
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