TM 5-822-12
Figure 4. Aggregate surfacing design curve for Class III airfields.
The sand subbase must be either nonfrost-susceptible
working platform for placement and compaction of
or of low frost susceptibility (S1 or S2). The filter layer
subbase. Compaction of subgrade will not change its
may or may not be necessary depending upon the type
frost-area soil support index, however, because frost
of subgrade material.
If the subgrade consists
action will cause the subgrade to revert to a weaker
principally of gravel or sand, the filter layer may not be
state. Hence, in frost areas, the compacted subgrade
necessary and may be replaced by additional base
will not be considered part of the layered system of the
course if the gradation of the base course is such that it
road or airfield which should be comprised of only the
meets filter criteria. However, for finer grained soils, the
wearing, base, and subbase courses.
filter layer will be necessary. If a geotextile is used, the
sand subbase/filter layer may be omitted as the fabric
g. Thickness of base course and filter layer
will be placed directly on the subgrade and will act as a
Relative thicknesses of the base course and filter layer
filter.
are
The subgrade should be
f. Compaction.
compacted to provide uniformity of conditions and a firm
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