The strength and the durability of pavement systems are directly related to the stiffness of the unbound and subgrade soil materials. The 1993 AASHTO flexible pavement design guide and more recently, the AASHTO ware software for the mechanistic-empirical design of pavements relies on the resilient modulus as the primary input parameter to characterize the stiffness of the subgrade and unbound base materials. Models that describe the modulus as a function of externally imposed stresses has been adopted in design procedures, but models that consider the internal stress state of the material at all levels of saturation have not been evaluated due to the lack of data available. This paper presents an evaluation of the Cary and Zapata (2010) model parameters, which includes the matric suction stress state of the material as a driver of the moisture soil retention capability. The evaluation was performed with data collected from resilient modulus testing on six different soil types at different moisture contents. Laboratory test performed include the soil-water characteristic curve, filter paper method and a comprehensive set of index properties. The resilient modulus tests were performed on soil specimens in accordance with the NCHRP 1-28 A protocol at different compaction conditions.