Assessment of resilient modulus testing methods and their application to design of pavements (FHWA-OK-91-08)

Resilient modulus (RM) is an important property of subgrade soils that accounts for repetitive loads due to vehicular traffic. Since AASHTO recommended its use in pavement design in 1986, various transportation agencies have devised procedures for testing and evaluation Of RM. A comprehensive literature search was conducted in this study with two objectives in mind: (i) to obtain information on current practices pertaining to RM testing of subgrade soils; and (ii) to compile information pertaining to the collective experience of various agencies in correlating RM with other engineering soil properties. Practices adopted by different transportation agencies in testing RM are not identical; some follow AASHTO guidelines, while others differ. The differences are centered around deviator stress, rate of loading, confining stress, moisture-density relationship, specimen preparation and stress sequence. The well known relationship between RM and CBR, proposed by AASHTO, does not correlate well for many soils. Efforts have been made by various researchers to correlate RM with other factors including clay, silt and organic carbon contents, plasticity index, liquid limit, group index, compressive strength, initial elastic modulus and confining pressure. Very limited efforts have been directed toward understanding the RM characteristics of bonded materials and aggregate bases.N