1 MARCH 2000
Figure 6-16. Air Freezing index/Surface Cover/Frost Penetration Relationship
f. Alternate Design Procedure. An alternate method of designing for the effects of frost is to reduce the
effective strength of the soil to compensate for the thaw-weakening period (similar to a reduced-strength
g. Methods for Reducing Frost Effects.
(1) Additional Ballast/Sub-ballast. If more than 40 percent of the total frost depth is in the frost
susceptible subgrade, nonfrost susceptible material (clean ballast or sub-ballast) must be added to the
(2) Geotextiles. Geotextiles can be used to prevent particle migration at the subgrade/sub-ballast
interface during the spring thaw. Contamination of an otherwise clean ballast and sub-ballast by
subgrade soil can turn a nonfrost susceptible material into a frost susceptible material. The application of
geotextiles is covered in TM 5-818-8 and AFMAN 32-8011.
(3) Insulating Material. Frost heaving may be reduced or eliminated by the use of insulating
materials. This may be particularly useful in areas with deep seasonal frost that lack nonfrost susceptible
soils and in areas with varying subgrade soil conditions that may result in differential heaving. Expanded