may be particularly true for flexible pavements containing much distress. Because of the time and effort involved, frequent

surveys of the entire feature may be beyond available manpower, funds, and time.

statistical sampling plan was developed to obtain an adequate estimate of the PCI determined by inspecting only a portion

of the sample units within normal size features (i.e., 20 + 5 slabs for rigid pavements, and 5,000 + 1,000 sq ft for flexible).

Use of the statistical sampling plan described herein will considerably reduce the time required to inspect a feature without

significant loss of accuracy. However, this sampling plan is optional, and inspection of the entire feature may be desirable

in some cases.

a. Determination of pavement feature. The first step in the condition survey is the designation of pavement features.

Each facility such as a runway, taxiway, etc., is divided into segments or features that are definable in terms of the same

design, the same construction history, the same traffic area, and generally the same overall condition. General features

can be determined from pavement design and construction records and can be further subdivided as deemed necessary

based on a preliminary survey. It is important that all pavement in a given feature be such that it can be considered

uniform. For example, the center part of some runways in the traffic lanes should be separate features from the portion

outside the traffic lanes.

b. Selection of sample units to be inspected. Assuming a normal distribution of data, the number of sample units to

be surveyed to provide a 95-percent confidence level can be determined from

2

N

(eq 4-1) n =

2

e

2

4 (N - 1) +

where

n = number of sample units to be inspected

N = total number of sample units in feature

= one standard deviation in PCI between sample units within the feature

e = allowable error in determining the true PCI

Data collected during the development of the PCI procedure gave average values of 10 and 15 for flexible and rigid

pavements, respectively. These values should be used for determining the number of sample units to be inspected unless

field data and experience indicate the higher or lower values would be more appropriate for military airfield pavements.

The number of samples n obtained from the equation is the minimum number to be inspected in a given pavement feature

in order to have 95 percent confidence that the PCI is within 5 points. The above equation is presented graphically in

figure 4-1 to simplify its use in application.

c. The minimum number of sample units that must be surveyed to obtain an adequate estimate of the PCI of a

feature is selected from figure 4-1. Once the number of sample units η has been determined from figure 4-1 the spacing

interval of the units is computed from

(eq 4-2) i = N

η

where

i = spacing interval of units to be sampled

N = total number of sample units in the feature

η = number of sample units to be inspected

Integrated Publishing, Inc. |