UFC 3-260-03

15 Apr 01

a flexible pavement using the procedures presented in chapter 5. Thus, when evaluating by the flexible

pavement evaluation method, it will be necessary to determine the physical properties that are required for

flexible pavement evaluations; that is, the quality of the asphaltic concrete portion of the overlay will have

to be established, as well as the CBR values of the subgrade and base course beneath the rigid base

pavement. As mentioned above, the rigid base pavement will be assumed to have a CBR of 100.

c. Evaluation Example for Army and Air Force. Evaluate a type A traffic area pavement having a

uniform thickness of a nonrigid overlay on a rigid pavement. A standard evaluation is to be accomplished

for 50,000 passes of the C-141 aircraft. The pavement consists of a 152-millimeter (6-inch) bituminous

overlay, a 152-millimeter (6-inch) rigid base pavement with a 4.1-MPa (600-psi) flexural strength, an

203-millimeter (8-inch) base course having a k of 81 kPa/mm (300 pci) and a CBR of 30, a subgrade

with a CBR of 10. Since the k value under the rigid pavement exceeds 54 MN/cubic meter (200 pci), it is

necessary to evaluate the pavement by both the nonrigid and the flexible evaluation methods to obtain the

highest allowable gross weight at the selected pass level.

(1)

Rigid Pavement Evaluation Method. The following steps are followed:

(a)

From figure 6-73, determine F to be 0.803.

(b)

Calculate the equivalent thickness by substituting in equation 6-6:

1

[0.33 (152) % 152] ' 252 *millimeters*, *using SI units*

0.803

1

[0.33 (6) % 6] ' 9.94 *inches*, *using IP units*

0.803

(c) Having determined the equivalent pavement thickness, the remainder of the evaluation

will be accomplished in the same manner as a plain concrete thickness using the equivalent thickness as

the existing thickness. Therefore, using the k on the base course and figures 6-13 and 6-31, the allow-

able load would be 100,000 kilograms (220 kips).

(2) Flexible Pavement Evaluation Method. Since the existing thickness of asphalt exceeds the

minimum thickness of 102 millimeters (4.0 inches) by 51 millimeters (2.0 inches), the thickness equivalen-

cies of paragraph titled "Selection of Thickness Values" must be applied. The resulting section for the

purpose of evaluation of the subgrade is then 102 millimeters (4.0 inches) of asphalt, 152 millimeters

(6.0 inches) of 100 CBR base and 320 millimeters (12.6 inches) of 30 CBR subbase on a 10 CBR sub-

grade. The allowable aircraft gross weight on the subgrade for this condition is 122,000 kilograms

(270 kips). To evaluate the subbase, the excessive asphalt is converted to an equivalent thickness of

base course resulting in a section above the subbase of 102 millimeters (4.0 inches) of asphalt and

211 millimeters (8.3 inches) of base course. This would result in an allowable load of 212,000 kilogram

(467 kips) for the subbase. The 152 millimeters (6.0 inches) of asphalt on the 100 CBR base course

would evaluate for 263,000 kilograms (580 kips).

(3) Controlling Evaluation. Regardless of the procedure used, the higher controlling weight of

either the flexible or rigid method would be used for the pavement evaluation. For this example, the

122,000 kilograms (270 kips) determined for the subgrade using the flexible pavement method would be

the controlling evaluation.

d. Evaluation Example for Navy and Marine Corps. Evaluate a primary traffic area pavement

having a uniform thickness of a nonrigid overlay on a plain concrete pavement. The evaluation is to be

6-12