273
E
12
+ t 3 ST
2
Eqn. 6.9
2
Figures 6.70 and 6.71 present the relationships between E and
Dx D4 for each of the weighting methods. There is very little
difference between modulus-deflection relationship for the standard
weighting method (Equation 6.8) and the Thenn de Barros1 formula
(Equation 6.9), as shown in Figure 6.70 and Figure 6.71, respectively.
It would appear that either method would be suitable for defining E12
although the difference between methods becomes significant at low E
values and high Dx D4 values (e.g., E12 < 34.0 ksi, and D1 D4 > 1.0
mil). Thus knowing E from Dj D^, and Ej from asphalt rheology (or
using Figure 6.64), E2 can be calculated using Equations 6.8 and 6.9. A
procedure incorporating the above and other layer moduli predictions for
routine pavement evaluation studies is presented in Appendix F.
The relationship between E3 and 04 D? is illustrated in Figure
6.72. The figure shows that the simplified format of Equation 4.15
could be used for a wider range of E3 values. Even though the results
of the regression analysis of Figure 6.72 is fairly good, the range in
E3 values is still narrow and limited to only two values below 20.0
ksi. Additional test data in the lower range would be helpful in either
verifying the validity of the E3 prediction equation or modifying the
regression equation.
Subgrade modulus prediction equations and the modified Dynaflect
sensor 10 deflection values are shown in Figure 6.73. The simplified
equation (Equation 4.35), as previously explained, was originally
developed using data collected in Quebec, Canada and Florida. Figure