1 MARCH 2000
b. Identifying Frost Susceptible Soils. For design purposes, the potential for ice segregation is often
expressed as a function of grain (or particle) size. Most organic, non-uniform soils containing 3 percent or
more by weight of particles smaller than 0.02 mm are considered frost susceptible. Gravel, well graded
sands and silty sands (especially those approaching the theoretical maximum density curve) that contain
1.5 to 3 percent of particles smaller than 0.02 mm should be considered possibly frost susceptible and
subject to laboratory frost-susceptibility tests. Considerable ice segregation can be expected in uniform
sandy soils with greater than 10 percent smaller than 0.02 mm. Figure 6-14 illustrates a method for
determining the frost susceptibility of soils.
Figure 6-14. General Method for Determining the Frost Susceptibility of Soils
c. Water Source. Usually, the water source will be an underlying groundwater table, a perched aquifer,
or infiltration from the overlying layers.
d. Frost Depth. Future track maintenance costs are reduced if the design depth of frost below the top of
the ballast is at least 60 percent of the expected local frost depth. The expected frost depth should be
established using local records, experience or building practices. If these are unavailable, use the
procedures in TM5-852-6/AFP 88-19, chapter 6.
e. Alternate Frost Depth Procedure.