UFC 3-260-02
30 June 2001
(c) Compute water content ratio r from Equation 20-13.
For r $ 2.0, for types A and B traffic areas, use r = 2.0 with Figure 20-6. For r $ 3.0, for types C
and D traffic areas use r = 3.0 with Figure 20-6. Determine the design combined base-course
thickness (b) and amount of subgrade frost penetration (s) for the combined base thickness.
Design Combined Base Thickness b
Subgrade Frost Penetration Depths
Traffic Area
mm (in.)
mm (in.)
A
432 (17)
114 (4.5)
B
432 (17)
127 (5.0)
C
457 (18)
127 (5.0)
D and Overruns
508 (20)
127 (5.0)
(d) Compare these design pavement thicknesses with those obtained with the
reduced subgrade strength design procedures.
In this case, the thicknesses required for traffic areas A, B, and C using the limited subgrade frost
penetration design are more economical than from the reduced subgrade strength design. For
traffic area D, even though the limited subgrade frost penetration design requires the greatest
thickness of pavement and base, it may still be the most economical design as it requires only
241 millimeters (9.5 inches) of PCC versus the 292 millimeters (11.5 inches) required by the
reduced subgrade strength design procedure. The designer must make a decision based upon a
comparison of costs between the PCC and the base material. The design pavement thickness
selection is shown below. The final thickness of PCC for the same base-course thickness for
nonfrost conditions is also shown. The thicker value of the two will be used.
Reduced Subgrade Strength Method
Limited Subgrade Frost Penetration
mm (in.)
mm (in.)
Traffic
Combined
Combined
Area
PCC
Base
Total
PCC
Base
Total
A
483 (19.0)
483 (19.0)
966 (38.0)
406 (16.0)
432 (17.0)
838 (33.0)
B
470 (18.5)
470 (18.5)
940 (37.0)
394 (15.5)
432 (17.0)
826 (32.5)
C
381 (15.0)
381 (15.0)
762 (30.0)
305 (12.0)
457 (18.0)
762 (30.0)
D
292 (11.5)
292 (11.5)
584 (23.0)
241 (9.5)
508 (20.0)
749 (29.5)
20-20
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