layers will differ as a function of the modulus of elasticity of each
layer.
2.2.4 Three-Layer System
Although Burmister's work provided analytical expressions for
stresses and displacements in two- and three-layer elastic systems, Fox
(38) and Acum and Fox (2) produced the first extensive tabular summary
of normal and radial stresses in three-layer systems at the intersection
of the plate axis with the layer interfaces. Jones (52) and Peattie
(89) subsequently expanded these solutions to a much wider range of
solution parameters. Tables and charts for the various solutions can be
found in Yoder and Witzcak (133) and Poulos and Davis (92). It should
be noted that the figures and tables for stresses and displacements have
been developed, respectively, for Poisson's ratios of 0.5 and 0.35, for
all layers, and on the assumption of perfect friction at all interfaces.
Hank and Scrivner (42) presented solutions for full continuity and
zero continuity between layers. Their solutions indicate that the
stresses in the top layer for the frictionless case (zero continuity)
are larger than the stresses presented for the case of full continu-
ity. In an actual pavement, the layers are very likely to develop full
continuity; hence, full continuity between layers should probably be
assumed.
Schiffman (100) extended Burmister's solution to include shear
stress at the surface for a three-layer system. Mehta and Veletsos (73)
developed a more general elastic solution to a system with any number of
loads. They extended the solution presented by Burmister to include
tangential forces as well as normal forces.