UFC 3-260-03
15 Apr 01
in the evaluation report, including the locations and descriptions of the objectionable roughness. Surface
elevations should be obtained at least once a month during the following winter.
a. The allowable gross load allowed during thaw-weakening periods is based on the assumption
that flight operations are continued at the same frequency in effect during the rest of the year. Allowable
gross loads for flexible pavements during the thaw-weakening period are determined by using FASSI
values with the evaluation curves in chapter 5 or the computer program APE. The applicable FASSI
values for the various frost groups of subgrade soils are shown in table 7-3. The FASSI values are used
as if they were California Bearing Ratio (CBR) values with the evaluation curves; the term CBR is not
applied to them, however, because being weighted average values for the annual cycle, their values can-
not be determined by CBR tests.
Table 7-3
FASSI Values for Various Frost Susceptibility Soils
Frost Group of Subgrade Soil
F1
F2
F3 and F4
Frost-Area Soil Support Index (FASSI)
9
6.5
3.5
b. Allowable gross loads on rigid pavements during the thaw-weakening period are determined by
using FAIR values with the evaluation curves in chapter 6 or the computer program APE. FAIR values
can be estimated from figure 7-6. The curves in figure 7-6 show the equivalent weighted average FAIR
values for an annual cycle that includes a thaw-weakening period in relation to the thickness of the com-
bined base. The FAIR values can also be estimated from the following equations:
English Units
S1 or F1 material: FAIR ((psi /in.) ' 4.2 % 10.8 base Course Thickness (inches)
(eq 7-5)
S2 or F2 material: FAIR ((psi /in.) ' 1.3 % 8.0 base Course Thickness (inches)
(eq 7-6)
F3 or F4 material: FAIR ((psi /in.) ' 1.6 % 5.9 base Course Thickness (inches)
(eq 7-7)
SI Units
S1 or F1 material: FAIR ((MN/m2/m) ' 1.13 % 116.4 base Course Thickness (meters)
S2 or F2 material: FAIR ((MN/m2)/m) ' 0.36 % 85.6 base Course Thickness (meters)
F3 or F4 material: FAIR ((MN/m2)/m) ' 0.44 % 63 base Course Thickness (meters)
FAIR values are used as if they were moduli of soil reaction, k , and have the same units. The term
modulus of soil reaction is not applied to them, however, because being weighted average values for an
annual cycle, they cannot be determined by a plate-bearing test. If the modulus of soil reaction, k , deter-
mined from tests on the equivalent base course and subgrade, but without frost melting, is numerically
smaller then the FAIR value obtained from figure 7-6, the test value should be used in the evaluation.
14. REDUCTION FACTORS FOR NONDESTRUCTIVE TESTING. The moduli of the subgrade during
thaw periods are reduced modulus values obtained during the nonfrost period. Reduction factors (RF) are
7-8
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