TM 5-822-5/AFM 88-7, Chap. 1
are listed in approximate order of decreasing bear-
sity. The order of listing of subgroups under groups
ing capacity during periods of thaw. There is also a
F3 and F4 does not necessarily indicate the order of
tendency for the order of the listing of groups to
susceptibility to frost heave of these subgroups.
coincide with increasing order of susceptibility to
There is some overlapping of frost susceptibility
frost heave, although the low coefficients of perme-
between groups. Soils in group F4 are of especially
ability of most clays restrict their heaving propen-
high frost susceptibility.
a. S1 and S2 groups. The S1 group includes
soils, they will generally exhibit less frost heave and
gravelly soils with very low to medium frost-
higher strength after freeze-thaw cycles.
b. Fl and F2 groups. The F1 group is intended
susceptibility classifications that are considered
suitable for subbase materials. They will generally
to include frost-susceptible gravelly soils that in the
exhibit less frost heave and higher strength after
normal unfrozen condition have traffic performance
freeze-thaw cycles than similar Fl group subgrade
characteristics of GM-, GW-GM-, and GP-GM-
Soils. The S2 group includes sandy soils with very
type materials with the noted percentage of fines.
low to medium frost-susceptibility classifications
The F. group is intended to include frostsusceptible
that are considered suitable for subbase materials.
soils that in the normal unfrozen condition have
Due to their lower percentages of finer-than-0.02-
traffic performance characteristics of GM-, GW-
millime- ter grains than similar F2 groups subgrade
GM-, GP-GM-, SM-, SW-SM-, or SP- SM-type
18-5
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