95
moduli and thickness of layers 1 and 2. Figures 4.14, 4.15, and 4.16
show that for a fixed t1 the relationships between Ex and D D^ are
not significantly affected by E3 and E^. Also, the plots suggest that
the effect of E2 becomes negligible as the thickness of the asphalt
concrete increases. This relationship was therefore used to develop
power law equations to predict E: with an estimate of E2 for different
layer combinations using the Dynaflect modified system.
The sequential development of layer moduli prediction equations
using the BISAR generated Dynaflect and FWD deflections is presented in
Section 4.3.2 for both NDT devices. Equations for the FWD used theore
tical deflections from a 9-kip FWD load. The methodology employed
involved the use of simple power law relationships and multiple linear
regression analysis (39) procedures.
4.3.2 Development of Dynaflect Prediction Equations
4.3.2.1 Prediction Equations for E^ Initial analysis of theo
retical Dynaflect deflection basins had indicated that E: and E2 were
essentially independent of E3 and E4 using Dj D^ as shown in Figures
4.14 through 4.16. Thus Ex could be expressed as a function of E2, t15
t and D D where D, and D, are deflections at sensors 1 and 4,
respectively, in the modified Dynaflect sensor array (see Figure 4.2).
The use of constant base course thickness (Table 4.1) removes the
influence of t2.
Power law relationships between E1 and Dx D^ for several combina
tions of t and E2 were developed. Regression analyses were then per
formed to establish intercepts and slopes for the linear trends. The
basic form of the regression equation used in the analyses was