UFC 3-260-02
30 June 2001
elevation of groundwater is about 1.5 meters (5 feet) below the surface of the subgrade. The
subgrade is a very fine silty sand with 20 percent finer than 0.02 mm by weight. The average
moisture content of the subgrade is 21 percent. The nonfrost design modulus of soil reaction is
27.1 MN/m3 (100 lb/in.3). The 90-day concrete flexural strength R is 4.83 MPa (700 psi).
(1) Reduced subgrade design.
(a) From Table 20-1, the subgrade is classified as F4 frost susceptible soil.
(b) Select 6 combined base-course thicknesses and obtain FAIR values from
Figure 20-1 or from Equation 20-3.
FAIR Values, MN/m3 (lb/in.3)
Combined Base Thickness, mm (in.)
102 (4)
7.6 (28)
152 (6)
10.6 (40)
203 (8)
13.7 (51)
305 (12)
19.7 (74)
457 (18)
29.5 (108)
610 (24)
38.6 (142)
(c) Use FAIR values with Figure 20-7 as though they were k values and determine
the thickness of PCC pavement.
Combined Base
Traffic Area PCC Thickness, mm (in.)
Thickness,
FAIR Value
MN/m3 (lb/in.3)
mm (in.)
A
B
C
D
102 (4)
7.6 (28)
693 (27.3)
688 (27.1)
572 (22.5)
450 (17.7)
152 (6)
10.6 (40)
671 (26.4)
666 (26.2)
546 (21.5)
432 (17.0)
203 (8)
13.7 (51)
653 (25.7)
648 (25.5)
531 (20.9)
419 (16.5)
305 (12)
19.7 (74)
622 (24.5)
617 (24.3)
508 (20.0)
399 (15.7)
457 (18)
29.5 (108)
594 (23.4)
589 (23.2)
485 (19.1)
379 (14.9)
610 (24)
38.6 (142)
574 (22.6)
572 (22.5)
467 (18.4)
363 (14.3)
(d) Plot base course versus PCC thickness for the different traffic areas as shown in
Figure 20-12. Locate equal or nearly equal thickness of PCC and combined base course as shown
in the figure. The minimum thicknesses for the base and PCC layers are as follows:
20-22
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