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pavement exhibits extensive cracking (e.g., alligator cracking), Ex will
be reduced considerably. Details pertaining to the use of Figure 6.64
will be presented in Chapter 8.
Tables 6.17 and 6.18 show that the base course and subbase moduli
from the Dynaflect are, respectively, higher than those for the FWD.
The corresponding comparison for the subgrade is shown in Table 6.19 and
this does not necessarily follow the trend of the base and subbase
layers. A comparison for all three layer moduli is shown in Figure 6.65
and Table 6.20. In Table 6.20, the ratio of the Dynaflect to FWD moduli
for all test sections are listed for the various layers. The good
agreement for the AC layer has already been discussed. For the base
course layer, the ratio ranges from 1.0 to 3.87. The 3.87 value oc
curred with the SR 12 test section in which the base course material was
a sand-clay mixture instead of the limerock material used for the rest
of the test pavements. The higher predictions of E2 from the Dynaflect
than FWD agrees with the findings of Bush and Alexander (23), and Wise
man et al. (130). These researchers found that the moduli of the base
course determined from FWD deflection basins were significantly lower
than those obtained from analyzing deflection basins produced by either
the Dynaflect, Road Rater, Pavement Profiler, or 16-kip vibrator. The
Pavement Profiler and 16-kip vibrator also operate on the steady-state
vibratory loading principles of the Dynaflect and Road Rater. The base
course moduli predictions obtained from this research therefore support
the belief that deflection basins produced by steady-state vibratory
loading devices result in higher base course moduli than those produced
by impulse loading devices such as the FWD.