TM 5-822-12
Figure 2. Aggregate surfacing design curve for Class I airfields.
a. Required thickness. Where frost susceptible
7. Frost area considerations
subgrades are encountered, the section thickness
In areas where frost effects have an impact on the
required will be determined according to the reduced
design of pavements, additional considerations
subgrade strength method. The reduced subgrade
concerning thicknesses and required layers in the
strength method requires the use of frost area soil
pavement structure must be addressed. The specific
support indexes listed in table 6. Frost-area soil support
areas where frost has an impact on the design are
indexes are used as if they were CBR values; the term
discussed in the following paragraphs; however, a more
CBR is not applied to them, however, because, being
detailed discussion of frost effects is presented in TM 5-
weighted average values for an annual cycle, their
818-2. For frost design purposes, soils have been
values cannot be determined by CBR tests. Figures 1
divided into eight groups as shown in table 5. Only the
through 4 are entered with the soil support indexes in
nonfrostsusceptible (NFS) group is suitable for base
place of CBR values to determine the required section
course. NFS, S1, or S2 soils may be used for subbase
thickness.
course, and any of the eight groups may be encountered
as subgrade soils. Soils are listed in approximate order
of decreasing bearing capability during periods of thaw.
6
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