Normalized resilient modulus model for subbase and subgrade based on stress-dependent modulus degradation

The flexible pavement system consists of layered structures. Each layer is composed of different materials and represents different response to loading. Successful pavement design, therefore, requires proper evaluation of mechanical properties for the sublayers, which can realistically describe the behavior of pavement substructures. The resilient modulus is an important mechanical property widely used for the analysis and design of flexible pavements. In this study, a normalized resilient modulus model applicable to both subbase and subgrade materials is proposed. A series of laboratory test results for subbase and subgrade materials are collected and analyzed to investigate effects of the confining and deviatoric stresses on the resilient modulus. Based on test results, a normalized degradation relationship of the resilient modulus as a function of normalized stresses is developed. Values of model parameters for the proposed model are also evaluated and presented. To check validity of the model, a finite element analysis is performed and compared with measured responses of pavement structures.