The purpose of this paper is to demonstrate the influence of granular material behaviour models in flexible pavement design, by comparison with measured response observed during wheel load tests on experimental pavements and with numerical simulations performed by the finite element method. The experimental pavements were instrumented during the construction phase with deformation gauges installed in bituminous, granular and soil foundation layers. The resilient behaviour of unbound granular materials was back analysed by wheel load test results, using different nonlinear elastic models, which were verified and calibrated by repeated load triaxial tests. Comparisons between the field results and numerical simulations have demonstrated the importance of a more accurate behaviour model for unbound granular materials in structural pavement analysis