Fundamental characterisation of the anisotropic resilient behaviour of unbound granular materials

The paper presents an in-depth investigation of the resilient behaviour of an unbound base material. It is based on the assumption that the material is non-linear and cross anisotropic. A testing programme that includes different incremental stress paths, principal stress ratios and confining pressures is proposed. The programme requires the use of a triaxial cell where both the vertical and horizontal stresses and deformations are either controlled or measured. The paper describes the analysis steps whereby only three material parameters, out of the five cross anisotropic parameters, can be obtained in the above conditions. Four specimens of a good quality base material were prepared in the laboratory and tested according to the above testing programme. The analyses of the tests show that: (1) The vertical modulus depends solely on the bulk stress, as expected for a good quality base material; (2) The vertical to horizontal Poisson's ratio and the horizontal parameter are also nonlinear and function of the first two stress invariants; (3) The material parameter functions from the incremental loading tests are different from those of the resilient modulus test; (4) The characterization is sensitive to the type of loading.