Multilayer solutions that calculate stresses, strains, and displacements in pavement structures caused by surface loading have been in existence for several years. However, most elastic layer computer software applications have been developed for mainframe computers. Recently, computational capabilities of the practicing engineer have been greatly enhanced by recent developments in personal computers. Results of this study involved development of an accurate and efficient solution to the multilayer problem. In addition, software was developed for use on a personal computer that included routines for backcalculating pavement layer moduli from measured surface deflections.

A convergence technique, employing a combination of closed form and numerical solutions, has been developed to provide accuracy of results at the surface of the pavement and near the load. Special methods of solving the system of boundary equations were developed to obtain the terms needed for the closed form part of the solution. Maximum efficiency has been obtained through an in-depth analysis of the parameters affecting accuracy and their relationship with the numerical integration step.

In its current form, the computer solution WESLEA is a fully competent three-dimensional solution that will handle up to five layers with varying interface conditions and a maximum of 20 loads. The fifth layer is semi-infinite and can be made stiff based on the choice of modulus of elasticity. A personal computer-based backcalculation program, WESDEF, has been developed utilizing the multilayer program. An evaluation of the new program is made through comparison of identical deflection data using the BISAR n-layered computer program.