30 June 2001
b. Army and Air Force Design.
(1) Equivalency factors. The use of stabilized soil layers within a flexible pavement provides
the opportunity to reduce the overall thickness of pavement structure required to support a given load.
An equivalency factor represents the number of millimeters (inches) of conventional base or subbase
that can be replaced by 25 millimeters (1 inch) of stabilized material. Equivalency factors will be
determined for Army and Air Force designs from Table 10-2 and for Navy and Marine Corps designs
from Table 10-3.
(2) Design. The design of a pavement having stabilized soil layers is accomplished through
the application of the equivalency factors to the individual unbound soil of a pavement. A conventional
flexible pavement is first designed, and then the base and subbase are converted to an equivalent
thickness of stabilized soil. This conversion is made by dividing the thickness of unbound material by
the equivalency factor for Army and Air Force airfields. For example, assume that a conventional
pavement has been designed consisting of 102 millimeters (4 inches) of AC, 254 millimeters (10 inches)
of base, and 381 millimeters (15 inches) of subbase for a total thickness above the subgrade of
737 millimeters (29 inches). It is desired to replace the base and subbase with cement-stabilized GW
material having an unconfined compressive strength of 6.27 MPa (910 psi). The equivalency factor from
Table 9-1 for the base-course layer is 1.15; therefore, the thickness of stabilized GW to replace
254 millimeters (10 inches) of base course is 254/1.15 (10/1.15) or 220 millimeters (8.7 inches). The
equivalency factor for the subbase layer is 2.3, and the thickness of stabilized GW to replace the
381-millimeter (15-inch) subbase is 381/2.3 (15/2.3) or 165 millimeters (6.5 inches). The thickness of
stabilized GW needed to replace the base and subbase would be 406 millimeters (16 inches).
c. All-Bituminous Pavement Section. Alternate procedures have been developed for design of
Army and Air Force airfield pavements composed entirely of AC. These procedures are based on
layered elastic theory and incorporate the concept of limiting tensile strain in the AC and vertical
compressive strain in the subgrade. The procedures are applicable for trial optional designs with the
approval of TSMCX, for Army airfields and the appropriate Major Command for Air Force airfields.
These design procedures are contained in Chapter 11.
8. SPECIAL AREAS. Areas such as overrun areas, airfield and heliport shoulders, blast areas, and
reduced load areas require special treatment as described in the following text for the various services.
a. Air Force Bases.
(1) Overrun areas. Overrun areas will be paved for the full width of the runway exclusive of
shoulders, and for a length of 305 meters (1,000 feet) on each end of heavy, modified heavy, medium,
light, and auxiliary runways and for 90 meters (300 feet) on each end of an assault landing zone runway.
Surface the overrun areas with double-bituminous surface treatment except for the first 45 meters
(150 feet) abutting the runway pavement end which will have a wearing surface of 51 millimeters
(2 inches) of dense graded AC. That portion of the overrun used to certify barriers or that must support
snow removal equipment may also be surfaced with dense graded AC. Design the pavement thickness
in accordance with Figures 10-17 to 10-32 herein, except that the minimum base-course thickness will
be 152 millimeters (6 inches). The strength of the assault overrun shall be equal to the strength of the
runway. Minimum base-course CBR values are as follows: