The Empirical-Mechanistic Design Method used for the structural design of pavements is based on the determination of stresses at critical points of the structure to establish if the deterioration will remain between some acceptable limits which do not affect the serviceability level offered to the user for the design period. Under traffic loads, soil responds with two different deformations: the resilient or recoverable one and the permanent or plastic one. This work presents a study on the resilient and plastic behavior of unbound granular soils based on laboratory test results carried out using both the repeated load triaxial apparatus and the monotonic triaxial shear strength apparatus. Test results of different types of sand and granular material used as pavement subgrades or subbases are shown; different constitutive models to predict the accumulation of permanent deformation are compared; and finally the evolution of the resilient modulus during the test is analyzed.