El (Predicted) = 75.612 + 0.848E1 (Actual) Eqn. 4.31
(N = 97, R2 = 0.848)
Deleting the cases with E4 equal to 0.35 and 200 ksi resulted in
El (Predicted) = 28.707 + 0.989E, (Actual) Eqn. 4.32
(N = 90, R2 = 0.934)
The improvement in R2 value suggests that the El prediction equa-
tions for Case 2 should be used with caution when E4 values are
extremely low or high.
Case 3: 10.0 < E < 85.0 ksi; and 7.0 < t < 10.0 in.
2 1
For this case, Equations 4.1, 4.6, and 4.7 were derived to predict E1.
As mentioned previously, these equations appear to be simple compared
with those for Cases 1 and 2. The relatively simple E, prediction
equations for Case 3 were developed using data for t = 8.0 in. only,
but it was found to be applicable for thicknesses between 7 and 10 in.
This also suggests that for thicker pavements, the effect of ti on E ,
E and D1-D4 becomes negligible, as shown in Figures 4.17 and 4.18.
The percent difference between actual and predicted E1 values for
Case 3 were within 6 percent. Only three pavements exceeded this,
having less than 10 percent error. When the predicted and true moduli
values were regressed, the following equation was obtained.
E1 (Predicted) = 2.896 + 0.991E1 (Actual) Eqn. 4.33
(N = 22, R2 = 0.998)