Abstract

In order to adequately design a pavement system, attention must be paid to the subgrade. This thesis attempts to formulate such a design method based on the expected traffic volumes, the subgrade material properties, and material behaviour. The methodology described in this thesis involves two main phases. The first phase develops a relationship between the vertical strain produced at the top of the subgrade and a combination of five axle loads and three base thicknesses. This relationship is based on constitutive equations and the finite element method. These fifteen relationships shown as strain contours are for a specific material, and can be used to find the critical strain for a given axle load and base thickness. The second phase of this thesis deals with the development of a pavement design method using vertical strain contour charts. These strain contour charts have been developed using constitutive equations and the finite element method for different types of soil parameters and behaviors. This method then utilizes equations from the Asphalt Institute design method to determine base thickness and the life of the subgrade. Numerical examples of the design method have been provided. A set of computer programs have been developed for the finite element analysis. These programs have been unified under a menu program (FINITE) and are capable of finding the stress-strain distributions in the subgrade