103
K
2
0.9399 + 0.00112(E )
2
Eqn. 4.7
In Equations 4.1 through 4.7, Ej and E2 are in ksi; t1 is in inches; and
is in mils. The equations for Case 3 appear to be simple com
pared to those for Cases 1 and 2. The accuracy of these equations,
neglecting the estimation error of E2, is discussed later in this chap
ter. It will also be shown later that the equations can be combined
into a simpler form when field measured Dynaflect deflection data are
evaluated.
4.3.2.2 Prediction Equation for E2 for Thin Pavements. Analysis
of data for thin asphalt concrete pavements (1.0 and 2.0 in.) indicated
that El has little effect on Dx for any specific value. Figure
4.19 shows that E2 versus D: D4 is not sensitive to changes in Er
This lack of sensitivity suggested that it would be more reliable to
develop an equation for the prediction of E2 using estimated values of
Ex without introducing significant errors. Therefore, E2 was esta
blished to be a function of E^ tlS and D: D4. The general form of
the equation is
Eqn. 4.8
where E2 is modulus of base course in ksi, and Kx and K2 relationships
are as shown in Case 4.