304
7.4.2 Correlation of Resilient Moduli with Cone Resistance
The average qc values determined from each layer were compared to
the respective NDT tuned layer moduli. The results of these comparisons
are illustrated in Tables 7.2, 7.3, and 7.4, for the base course, sub-
base, and subgrade layers, respectively. The ratios of tuned moduli to
cone resistance presented in Tables 7.2 to 7.4 indicate that variability
increases from E2 through E3 to E However, significantly high ratios
were obtained for the base course and subbase layers for some of the
pavements. For example, the SR 12 pavement had a ratio of 61.29 using
the Dynaflect tuned E2 (Table 7.2). The corresponding FWD E2 to qc
ratio, 15.83, does not differ much from the others in the FWD column.
Also, the plate loading test results gave an E2 value of 43,000 psi (see
Table 6.17) as compared to the NDT tuned values of 120,000 and 31,000
psi, respectively, with the Dynaflect and FWD deflection responses.
Thus, the FWD prediction of the base course modulus on SR 12 test
section may be more realistic than that of the Dynaflect. Pavement
sections and layers having extremely high or low ratios were excluded in
subsequent analysis of the data.
Regression analyses were performed between resilient (or tuned NDT)
moduli and cone resistance. The results are summarized in Table 7.5.
The results suggest that the correlations are good for the base and
subbase layers but poor for the subgrade. Also, the results for the
combined data are similar to those for the base and subbase layers as
compared to the subgrade layer. The poor correlation in the subgrade
could be due to the natural variability in the subgrade soils compared
to the essentially homogeneous base and subbase materials. The tech-
nique of determining the subgrade layer might have also affected the