Background Discussion of Mechanistic-Empirical Approach and CalME Models

The Mechanistic-Empirical approach to pavement design makes use of fundamental physical properties and a theoretical model to predict the stresses, strains and deflections, i.e. the pavement response, caused by a load on the pavement, as illustrated below. If the basic assumptions with respect to materials and boundary conditions are correct, this method is valid anywhere and may be used to correctly predict the response for any combination of loads, climatic effects and materials.

In the second part of the approach the pavement response is used with empirical relationships to predict the pavement performance:

In the Classical Mechanistic-Empirical method the pavement response is only calculated for the initial pavement condition (using different undamaged properties of pavement layers across the seasonal conditions of a year) and the empirical relations predict the number of loads to failure, through cracking, rutting or roughness using Miner’s Law. The Classical Mechanistic-Empirical method is used for asphalt pavement design in the Mechanistic-Empirical Pavement Design Guide (link) developed as part of the NCHRP 1-37A project, the Asphalt Institute method (current method, first version in 1982), the Shell Method (current method, first version in 1963, addition of seasonal properties in 1978).