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equations could be applied to an expanded range of parameters without
introducing much error. The prediction accuracy of these equations and
others are discussed in the next section.
4.4 Accuracy and Reliability of NDT Prediction Equations
The previous section presented several layer moduli prediction
equations for both the Dynaflect and FWD testing systems. The equations
are theoretical in the sense that they were developed from theoreti
cal ly-derived deflections (using the BISAR computer program), layer
thicknesses and moduli. The prediction accuracy of these equations are
assessed in this section.
The various equations were used to predict and evaluate prediction
errors. This was achieved by relating predicted moduli values to the
true or actual values. High prediction errors were deleted from the
data set and the remaining values were correlated to the actual values
of moduli originally selected for analysis. In general, prediction
errors of the order of 10 percent were considered to be compatible with
the variabilities commonly noted in field deflection-basin measurements.
4.4.1 Prediction Accuracy of Dynaflect Equations
4.4.1.1 Asphalt Concrete Modulus, Er The complexity of devel
oping a generalized equation to predict Ex for varying t1 and from
D -D^ resulted in the development of three equations to cover the dif
ferent ranges of E2 and tx (Equations 4.1 through 4.7). The accuracy of
these equations is discussed below.
Case 1: 10.0 < E < 30.0 ksi; and 3.0 < t < 6.0 in.
2 1