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6.6.1 Comparison of Deflection Basins
Figures 6.50 through 6.63 show comparisons of the field measured
FWD and Dynaflect deflection basin for each test section. The deflec
tions are normalized to an equivalent 1000-lb. load level. Deflection
basins normalized with respect to a standard load level are very helpful
in comparing NDT devices that apply different loads to the pavement.
Normalization of the FWD deflection basins, as illustrated in the plots,
is also another way of assessing linearity and stress dependency of the
load-deflection response. The figures indicate that FWD deflections
measured at about 7.0 kips load levels are very close to those measured
around 9.0 kips for all test sections. This would suggest that line
arity is achieved at FWD loads beyond 6.0 kips as postulated in Section
6.5.5.
In comparing the Dynaflect deflection basin to the FWD deflection
basins for each test section, the following three trends can be differ
entiated from the normalized plots:
1. Pavements which have FWD deflections greater than the Dynaflect
deflections. Test sections in this group are SR 26C, US 301, US
441, and SR 12. The normalized plots for these pavement sections
are illustrated in Figures 6.50 to 6.53.
2. Pavements which exhibit the reverse of the above, that is, Dynaflect
deflections are greater than those of the FWD. These are SR 26B, SR
15A, and SR 715 test sites and they are shown in Figures 6.54, 6.55,
and 6.56, respectively. Note that the SR 715 site (Figure 6.56) had
similar FWD normalized deflection basins, confirming the linear load
response diagram of Figure 6.9. The different Dynaflect deflection
basin could therefore be due to differences in NDT devices.