Unlike conventional pavements which rely on upper stiff layers (asphalt or concrete) to bear and spread traffic loads, the unbound aggregate inter-layer in an inverted pavement plays a major role in the mechanical response of the pavement structure. The boundaries imposed on the unbound aggregate base in an inverted pavement structure change radically from those in conventional pavements. Therefore, current empirically derived design methods are unsuitable for the analysis of inverted pavement structures. Given the critical role of the unbound aggregate base and its proximity to the surface (high stresses), new laboratory and field tests have been developed to characterize the stress-dependent stiffness of the unbound aggregate base. A complementary numerical study that incorporates state-of-the-art concepts in constitutive modeling of unbound aggregates is used to analyze experimental results and to develop preliminary guidelines for inverted base pavement design.nlike conventional pavements which rely on upper stiff layers (asphalt or concrete) to bear and spread traffic loads, the unbound aggregate inter-layer in an inverted pavement plays a major role in the mechanical response of the pavement structure. The boundaries imposed on the unbound aggregate base in an inverted pavement structure change radically from those in conventional pavements. Therefore, current empirically derived design methods are unsuitable for the analysis of inverted pavement structures. Given the critical role of the unbound aggregate base and its proximity to the surface (high stresses), new laboratory and field tests have been developed to characterize the stress-dependent stiffness of the unbound aggregate base. A complementary numerical study that incorporates state-of-the-art concepts in constitutive modeling of unbound aggregates is used to analyze experimental results and to develop preliminary guidelines for inverted base pavement design.