UFC 3-260-03

15 Apr 01

topographic conditions that will cause deviations from general freezing index values shown on this map;

assistance for this adjustment can be obtained through Headquarters, U.S. Army Corps of Engineers

(CEMP-ET), the appropriate Air Force Major Command, or the appropriate NAVFAC Headquarters. DFI

for sites in Eurasia can be roughly estimated from the mean freezing indices in figure 7-3 and using the

following equation. The mean freezing index from figure 7-3 must be multiplied by 13.33 to convert from

EF days to EC hours. This equation could also be used at other sites where the mean freezing index is

known. These data are available in WORLDINDEX.

(*DFI*) ' 429 % 1.143 *mean freezing index *(E*F days*)

(eq 7-1)

(*DFI*) ' 5,718 % 1.143 *mean freezing index *(E*C hours*)

10. DETERMINE FROST SUSCEPTIBILITY OF BASE, SUBBASE, AND SUBGRADE LAYERS. Deter-

mine if the base/subbase and/or subgrade is frost susceptible. Table 7-1, will be used to identify the frost

susceptibility of the soil. Soils are listed in approximate order of increasing frost susceptibility and

decreasing bearing capacity during periods of thaw.

11. EVALUATE PAVEMENT FOR COMPLETE FROST PROTECTION. The combined base thickness

required to prevent freezing into the subgrade with respect to the design freezing index is determined from

the computer program MODBERG (available through the PCASE bulletin board). Frost penetration

depths determined from MODBERG are measured from the pavement surface which must be free of

snow and ice during the winter. If the depth of frost penetration exceeds the thickness of surface and

combined base and subbase, the pavement is not protected from frost and should be evaluated for frost

effects.

(eq 7-2)

where

c = design thickness of combined base for complete frost protection (from MODBERG)

d = thickness of pavement and combined base for complete frost protection

p = thickness of surface layer

a. Determine whether the combined base thickness (x) under the pavement being evaluated is

sufficient to protect the subgrade from freezing. This is accomplished by comparing (x) with (c).

b. If (x < c), the evaluated pavement structure is inadequate for complete frost protection. If there

are no indications of frost action, then evaluate the pavement structure for limited subgrade frost pene-

tration. If there are indications of frost action, then evaluate the pavement structure with the reduced

subgrade strength approach described below.

c. If (x $ c) or (x $ 1,524 - p) or the base, subbase, and or subgrade is classified as NFS, S1, or S2

and there are no surface indications of frost action, use the nonfrost evaluation procedure. If there are

indications of frost action, evaluate pavement structure with the reduced subgrade strength approach.

7-5