UFC 3-260-02
30 June 2001
the F-15, 4,000 passes of the C-17, and 4 pass of the B-52. (Since the B-52 is included in the design,
the runway must be 61 meters (200 feet) wide.) On-site and laboratory investigations have yielded the
following data required for design: (1) the subgrade material is classified as a silty sand (SM); (2) the
modulus of soil reaction, k, of the subgrade is 54 kPa/mm (200 pci); (3) a nearby source of crushed
gravel meets the requirements for base course; (4) frost does not enter subgrade material; and
(5) 90-day concrete flexural strength, R, is 4.8 MPa (700 psi).
b. Example Design, Slab on Grade. Figure 12-8 is entered with the subgrade k = 200 pci, concrete
design flexural strength R = 700 psi, and the pavement thickness is determined for the various traffic
areas and overruns as follows:
Thickness, mm (in.)1
Traffic Area
406 (16.0)1
A
B
406 (16.0)
C
302 (12.0)
D and overruns
229 (9.0)
1
Fractional values would be rounded up to the nearest full- or half-inch for design.
c. Example Design, Slab on Unbound Base. For comparison purposes, designs are developed
below for three base-course thicknesses. Field plate bearing tests conducted in a test section to
establish the modulus of soil reaction for three thicknesses of base course give k values of 68 kPa/mm
(250 pci) for a 152-millimeter (6-inch) base, 81 kPa/mm (300 pci) for a 305-millimeter (12-inch), and
95 kPa/mm (350 pci) for 460-millimeter (18-inch) base. These values are supported by Figure 8-1 and
are thus selected for design. Figure 12-8 is entered with the design flexural strength, modulus of soil
reaction, and traffic areas to determine the required concrete pavement thicknesses. Thicknesses for
shoulders were determined from Figure 12-17. The thicknesses for this example are summarized as
follows:
Modulus of
Thickness, mm (in.)
Foundation
Soil Reaction
Shoulders1
Condition
kPa/mm (pci)
A
B
C
D & Overruns
(1)
(2)
(3)
(4)
(5)
(6)
(7)
150-mm (6-in.)
68
370
370
290
215
150
base
(250)
(14.5)
(14.5)
(11.5)
(8.5)
(6)
300-mm (12-in.)
81
340
340
260
200
150
base
(300)
(13.5)
(13.5)
(10.5)
(8.0)
(6)
460-mm (18-in.)
95
330
320
250
200
150
base
(350)
(13)
(12.5)
(10)
(8.0)
(6)
Note: Final thickness should be rounded values.
1
Use minimum thickness of 150 millimeters (6 inches) for shoulders.
The final selection of concrete pavement thickness must be based upon a study of the cost of importing
and placing base course versus savings in concrete pavements.
12-3
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