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repeated for all layer moduli and thicknesses. The NDT device used in
the parametric study was the FWD with a 9-kip loading and sensor spacing
as previously described. However, the findings also apply to the
Dynaflect loading system, under the principle of superposition and
linear elastic theory.
Figures 4.4 through 4.10 show the effect of change of either
modulus or thickness on the FWD deflection basins. The rate of change
of deflections is most pronounced with changes in E4, as compared with
the moduli of the upper pavement layers. In the case of the layer
thicknesses, the effect is most apparent with changes in the base course
thickness, t2. It is possible that the t2 effect was due to the high E2
relative to E3 and E .
Table 4.2 shows the percent change in deflections as a result of
doubling or halving each layer modulus while keeping the other para
meters unchanged for the pavement section shown in Figure 4.3. The
table shows that changes in E4 affect the deflections to the greatest
degree. The percent change in deflection is highest for any sensor
position when the E4 value is changed. This change with regard to E4
also increases substantially for the sensors further away from the load
center. The table thus suggests that E4 contributes the most to the FWD
deflections.
Similar comparisons were also made for changes in deflections for
tl values of 1.5 and 6.0 in. The effect of layer thicknesses, tx, t2,
and t3, on the theoretical FWD deflections were also studied and the
results are summarized in Table 4.3. In this table, t2 seems to have
the most effect. The effect of tx on the deflections becomes negligible
when the original value (tx = 3.0 in.) is halved.