9.4.1.1 Routine Pavement Analysis
In practice much routine pavement design is carried out as catalogue-based design. Nevertheless, routine structural analysis and design methods are used as supplemental design methods where the pavement is considered as a multi-layered elastic system (Amadeus Project, 2000). The layers are characterised by Young’s modulus, Poisson ratio and thickness. The simplest model for the stress-strain behaviour of isotropic materials is based on linear elasticity, which is described by Hooke’s law. In two or three dimensions, the model is written:
°ij = Ejr (9.1)
where oij, ей, Eeijkl are respectively members of the stress, strain and stiffness tensors а, є and Ee.
A symmetric stiffness matrix is used to describe the constitutive equations in those cases. As a road pavement is a layered structure, the material behaviour might be non-isotropic, with different stiffnesses in horizontal and vertical directions. Thus, the constitutive matrix is described with more independent parameters, which are also difficult to determine in a laboratory test. Hence, materials are usually considered isotropic. If the layers are not too thin, this might be a reasonable simplification.
