Characterization of Subgrade Resilient Modulus for Virginia Soils and its Correlation with the Results of Other Soil Tests

About the report:

In 2004, the Guide for the Mechanistic-Empirical Design of New & Rehabilitated Pavement Structures (MEPDG) was developed under NCHRP Project 1-37A to replace the currently used 1993 Guide for Design of Pavement Structures by the American Association of State Highway and Transportation Officials, which has an empirical approach. Implementation of the MEPDG requires the mechanistic characterization of pavement materials and the calibration of performance prediction models by the user agencies. The purpose of this study was (1) to determine the resilient modulus values for Virginia's subgrade soils for input into MEPDG design/analysis efforts, and (2) to investigate the possible correlation of the resilient modulus with other soil properties. Although the MEPDG provides default values and correlations for resilient modulus, they are based on a limited number of tests and may not be applicable for Virginia soils and aggregates. The possible correlation of the resilient modulus with other soil properties was investigated because such correlations could be used for smaller projects where costly and complex resilient modulus testing is not justified. More than 100 soil samples from all over Virginia representing every physiographic region were collected for resilient modulus, soil index properties, standard Proctor, and California Bearing Ratio testing. Resilient modulus values and regression coefficients (k-values) of constitutive models for resilient modulus for typical Virginia soils were successfully computed. There were no statistically significant correlations between the resilient modulus and all other test results, with the exception of those for the quick shear test, for which the correlation was very strong (R2 = 0.98). The study recommends that the Virginia Department of Transportation's Materials Division (1) implement resilient modulus testing for characterizing subgrade soils in MEPDG Level 1 pavement design/analysis, and (2) use the quick shear test to predict the resilient modulus values of fine soils using the relationships developed in this study for MEPDG Level 2 design/analysis.

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