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Other than one test site (SR 80 Section 2), the D10 values pro
vided an excellent, highly reliable relationship (Figure 6.69). How
ever, the slope of 0.95 suggests that predicted deflections are about 5
percent less than measured 01Q values. The discrepancy occurs because
the straight line log-log relationship for predicting E4 from D1() (stan
dard D5) tends to be a curvilinear (hyperbolic) relationship for E4
values below 10.0 ksi or above 100.0 ksi (see Figure 2.8).
6.7.2.2 Development of Simplified Layer Moduli Equations. Si nee
/
the tuned layer moduli provided predicted Dynaflect deflections which
correlated exceedingly well with the measured deflections, regression
analyses were performed to assess the relationship between
a) Composite modulus of asphalt concrete and base course layers
(E12) and Dj D4
b) Subbase or stabilized subgrade modulus (Eg) and D4 D?
c) Subgrade modulus (E4) and D1Q.
As mentioned previously, these sensor deflections were selected from the
analytical study on the basis of being related to the moduli of specific
layers. It was necessary to combine the asphalt concrete and base
course moduli because the analyses had indicated that no sensor location
or combination of sensor deflections were suitable for separation of Ex
and E2. The series of equations (Equation 4.1 through 4.10) developed
for prediction of either Ej or E2 from D1 D4, with a reasonable esti
mate of E2 or E respectively, albeit their high degree of prediction
accuracy, were considered to be too complex for routine evaluation of
pavements. Therefore, it was necessary to simplify the various £1 and
E2 prediction equations. The approach used is described below.