103
K = 0.9399 + 0.00112(E ) Eqn. 4.7
2 2
In Equations 4.1 through 4.7, E1 and E2 are in ksi; t1 is in inches; and
D D 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 D1 D4 for any specific value. Figure
4.19 shows that E2 versus Di D4 is not sensitive to changes in El.
This lack of sensitivity suggested that it would be more reliable to
develop an equation for the prediction of E2 using estimated values of
El without introducing significant errors. Therefore, E2 was esta-
blished to be a function of El, t1, and D, D4. The general form of
the equation is
-K
E = K (D D ) 2 Eqn. 4.8
2 1 1 4
where E2 is modulus of base course in ksi, and K, and K2 relationships
are as shown in Case 4.