TM 5-822-5/AFM 88-7, Chap. 1
about 2 to 3 inches, it will usually be economical to
and subbase) to contain completely the zone of
adopt for design the thickness given by figures D-2,
freezing can be determined from figure D-3, which
and to place the insulation directly on the subgrade.
shows the total depth of frost for various freezing
If more than about 2 to 3 inches of insulation are
indexes, thicknesses of extruded polystyrene
required to prevent subgrade freezing, it usually will
insulation, and base courses. The thickness of
be economical to use a lesser thickness of
subbase needed to contain the zone of freezing is
insulation, underlain by subbase material (S1 or S2).
the total depth of frost penetration less the total
Alternative combinations of thicknesses of extruded
thickness of pavement, base, and insulation.
polystyrene insulation and granular material base
D-2
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