UFC 3-260-03
15 Apr 01
pavement could have either "A" or "B" traffic depending on its use. Location of traffic areas depends on
the airfield class or type as defined in TI 825-01/AFM 32-1124(I)/NAVFAC DM 21.10, for the Army and
Air Force and in MIL-HDBK-1021/2 for the Navy and Marine Corps.
b. Pavement Type and Construction. After the pavements have been categorized by traffic area,
further subdivide each area, if necessary, into features having the same pavement type and construction.
Each area should be assigned a feature designation denoting the feature type (runway, taxiway, or apron),
the feature number (numerical identification within a given feature type), and the type of traffic area. Fig-
ure 4-1 illustrates proper feature identification and designation for a typical airfield.
5. STEP 2 (SELECT REPRESENTATIVE DEFLECTION SECTIONS). Either all basins, selected
basins, or a representative deflection basin is selected for each pavement feature to be evaluated.
Depending on the speed of the computer systems used, all basins or a representative basin may be
analyzed for each pavement section. For faster computer systems it is recommended that all basins be
analyzed and the mean modulus value for each layer will be used for the pavement evaluation. Simply
taking the average of each deflection reading is not acceptable because high or low values disturb the
mean and change the shape of the basin. The computations which are made by the computer program
BASIN are as follows:
a. NDT data are grouped into areas of equivalent impulse stiffness modulus (ISM). ISM is defined
as the force or load in kips divided by the deflection measured at the center of the load in inches.
Although a pavement feature may supposedly be of the same type and construction, it should be treated
as more than one pavement group when the strength characteristics measured in one section of the fea-
ture are greatly different from those in another section. An ISM is computed from the basin data to pro-
vide a qualitative stiffness comparison between test points and between pavement sections. The current
procedure is to plot the ISM values along the length of the feature and visually determine if a change in
strength exists.
b. Measured deflections are normalized to a common load. In most cases, the NDT loading will
vary slightly from test to test. To eliminate the effects of this variability, deflections are normalized with
respect to load before the basins are compared. This is accomplished by multiplying each deflection by
the load ratio (largest load measured within the feature divided by the load at which the deflection was
obtained).
c. The geometric average deflection is computed for each sensor offset distance within a pavement
feature.
d. The area of each deflection basin is determined as illustrated in figure 4-2. Only the hatched
area (under the measured portion of the basin) is considered in this computation, and the area between
two sensors is assumed trapezoidal.
e. Compute the average deflection basin area.
f. Although not used in determining the representative basin, an estimate of the modulus of sub-
grade reaction, k , beneath rigid and nonrigid overlay of rigid pavements can be determined by computing
the volume of the deflection bowl as illustrated in figure 4-3. The k value obtained in this manner is only
an estimate, and it should be noted that a substantial portion of the area used in the computation is in the
extrapolated range.
g. Compute an error function. An error function is computed as:
4-2
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