The third school of thought contends that layered elastic theory,

 when used with certain combinations of pavement moduli, predicts tensile

 stresses in granular base layers, even if gravity stresses are also

 considered (16,45,112). Instead of using a layered approach, this group

 prefers a finite element model in which the nonlinear responses of the

 granular and subgrade materials are accurately characterized. Again,

 the asphalt concrete layer is considered to be linear elastic. The

 ILLI-PAVE finite element back-calculation program (45) is a classic

 application of this theory.

 In the finite element approach discussed above, researchers have

used, with limited success, various failure criteria and in some cases

arbitrary procedures to overcome the problem of tensile stresses

(16,112). For example, Brown and Pappin (16) used a finite element

program called SENOL with a K-0 contour model and found it to be capable

of determining surface deflections and asphalt tensile stresses but

unable to determine the stress conditions within the granular layer.

The asphalt layer was characterized as elastic with an equivalent linear

modulus. They therefore concluded that the simplest approach for design

calculations involves the use of a linear elastic-layered system pro-

vided adequate equivalent stiffnesses are used in the analysis. This

conclusion is shared by other investigators (10,61,96,97) and is the

philosophy behind the work presented in this dissertation.