UFC 3-260-03
15 Apr 01
(equation 7-2) as the abscissa and, at the applicable value of r , find the base/subbase (include drainage
layer(s) thickness b for limited frost penetration into the subgrade or use equation 7-4. If the base/
subbase thickness (x) at the evaluated site is equal to or greater than b or equal to or greater than
1524 mm (60 inches) minus the pavement thickness, the pavement is adequately protected against
detrimental frost action.
b'cf
(eq 7-4)
where
b = combined base thickness for limited subgrade frost penetration
f = factor from table 7-2
c = design thickness of combined base for complete frost protection (from MODBERG
computer program)
Table 7-2
Values for Different Water Content Ratios
Water Content Ratio (r)
f
0.6
0.881
0.8
0.850
1.0
0.806
1.2
0.781
1.4
0.756
1.6
0.725
1.8
0.706
2.0
0.644
2.5
0.613
3.0
0.550
c. Check the surface for any indications of frost action. If there are no indications of frost action,
then use the nonfrost evaluation method. Otherwise evaluate the pavement structure with the reduced
subgrade strength approach discussed below.
d. If all the pavements being evaluated at an airfield are adequately protected against frost action,
or if the airfield is located where frost is not a problem, a note to that effect will be placed at the bottom of
the summary.
13. EVALUATE PAVEMENT FOR REDUCED SUBGRADE STRENGTH. If determined that a pavement
is not adequately protected against detrimental frost action, the procedures described below will be used
in making frost evaluations. The frost evaluation will be based on the reduced strength of the subgrade,
using FASSI or FAIR values as described below. Such evaluation will be modified, as appropriate, based
on pavement performance history. At the time of maximum heave, the surface roughness of pavement
constructed over F4 subgrade soils, and in some instances over F3 soils, may be objectionable for aircraft
with high landing and takeoff speeds. If experience indicates this is the case, this fact should be indicated
7-7
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