Civil Engineering Association

Estimating Stiffness of Subgrade and Unbound Materials for Pavement Design

The new Mechanistic Empirical Pavement Design Guide (MEPDG) and other existing pavement design guides use resilient modulus as the primary input parameter when characterizing stiffness of subsoils and unbound bases. Resilient modulus of soils is typically determined either by using laboratory tests or field tests. This report was prepared to describe the significance of the resilient modulus property, various methods of determining this property of subsoils and unbound bases, and the application of this parameter in the MEPDG. The report will be of interest to design, geotechnical and materials engineers and technicians. Information collected in this synthesis was based on a comprehensive literature review, surveys of pavement design, materials and geotechnical engineers from state departments of transportation (DOTs), and selected interviews. Information collected also included research reports from studies conducted by several state DOTs.