2.2.5 Multilayered or N-Layered Systems
A general analysis of a multilayered system under general condi-
tions of surface loading or displacement, or both was developed indepen-
\
dently by Schiffman (99) and Verstraeten (125). Schiffman (99) con-
sidered the general solutions for stresses and displacements due to non-
uniform surface loads, tangential surface loads, and slightly inclined
loads, but no numerical evaluations were presented. Verstraeten (125)
presented a limited analysis of the four-layered elastic problem. He
first derived expressions for the stresses and displacements for the
general case and performed numerical calculations for the particular
case of four-layered systems with continuous interfaces. The analysis
by Verstraeten included not only a uniform normal surface stress, but
also two types of surface shear stresses: (1) uniform one-directional
shear stress and (2) a uniform centripetal shear stress.
Recently, the Chevron Research Corporation (74) and the Shell Oil
Company (32) have developed computer programs for multilayered solutions
of the complete state of stress and strain at any point in a pavement
structure. Notable programs of interest are the BISTRO and BISAR pro-
grams by Shell (32), and the various forms of CHEVRON program by the
Chevron Research Corporation. These computer solutions are essentially
an extension of Burmister's work that permit the analysis of a structure
consisting of any number of layers supported by a semi-infinite sub-
grade, and under various loading conditions. In reality, it is only the
CHEVRON N-LAYER program (74) which is suitable for any number of layers.
All the others are restricted to a maximum number of layers. BISAR
(32), for example, can handle nine pavement sub-layers of known thick-
nesses plus the semi-infinite subgrade or bottom layer.