UFC 3-260-03
15 Apr 01
8. PAVEMENT CLASSIFICATION NUMBER. In addition to evaluating airfield pavements for allow-
able load, using the above procedures, it is also necessary to report weight-bearing capacity of pave-
ments in terms of the PCN. The PCN can then be compared with an aircraft classification number
(ACN) to determine if a pavement can support a particular aircraft. Values of ACN for given aircraft can
be obtained from the aircraft manufacturer or from the locations presented in chapter 9. The PCN is
presented in chapter 8.
9. EVALUATIONS FOR ARID REGIONS. The danger of saturation beneath flexible pavements is
reduced when the annual rainfall is less than 381 millimeters (15 inches), the water table (including
perched water table) is at least 4.6 meters (15 feet) below the surface, and the water content of the
subgrade will not increase above the optimum as determined by the ASTM D 1557 compaction test.
Under such conditions, the total design thickness of the pavement, when based on a soaked CBR, can
be reduced 20 percent. This reduction will be subtracted from the thickness of the select material or the
subbase course having the lowest design CBR value. Therefore, when flexible pavements are evalu-
ated using a soaked CBR value, the total thickness above the subgrade will be increased 25 percent
before entering the evaluation curves. This increase in thickness will be added to the select material or
the subbase course having the lowest CBR or to the same layer in which the reduction was made in the
design analysis. This increase in thickness would not apply for evaluations using in-place data.
10. EVALUATIONS FOR FROST CONDITIONS. If the existing soil, water, and temperature conditions
are conducive to detrimental frost effects in the base-course or subgrade materials, then the pavement
evaluation will be based on frost-area soil support indices as given in chapter 7 of this manual.
11. EVALUATIONS FOR STABILIZED LAYERS. Stabilized layers are incorporated in the design of
pavement sections to make use of locally available materials that cannot otherwise meet the criteria for
base or subbase courses. Materials must meet the requirements in TM 5-822-14/AFJMAN 32-1019.
When stabilized layers are used in design, equivalency factors assigned to the material result in a reduc-
tion in thickness requirements as compared with an unbound base course or subbase course. There-
fore, for evaluating a stabilized layer, an equivalency factor is applied that results in an increase in
thickness of the layer. Equivalency factors are determined from table 5-1 for the Army and Air Force and
from table 5-2 for the Navy and Marine Corps. If no information is available on the condition and
strength of the stabilized layer, it should be treated as a high-quality granular layer. If ECP or DCP
results indicate the layer is well stabilized (refusal for DCP), then the layer should be considered for the
equivalency factors. As an example, assume that an Air Force pavement structure determined from a
test pit consisted of a 101-millimeter (4-inch) asphaltic concrete, a 203-millimeter (8-inch) bituminous
concrete base, and an 203-millimeter (8-inch) cement-stabilized gravelly clay subbase with an
unconfined compressive strength of 48 MPa (700 pounds per square inch). From table 5-1, the
203-millimeter (8-inch) bituminous concrete base equivalency factor is 1.15 which would increase the
thickness of the stabilized base for evaluation to 233 millimeters (9.2 inches). From table 5-1, the
203-millimeter (8-inch) cement-stabilized subbase equivalency factor is 2.0 which would increase the
thickness of the stabilized subbase for evaluation to 406 millimeters (16 inches).
5-7
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