Models to Estimate Subgrade Resilient Modulus for Flexible Pavement Design (05-0236)
Ashraf M. Rahim, California Polytechnic State University, San Luis Obispo
K. P. George, University of Mississippi

Mechanistic pavement design procedures require characterization of each material in the pavement structure in terms of resilient moduli. Repeated triaxial load tests on cylindrical disturbed/undisturbed samples, yielding a resilient modulus, are frequently used for characterizing subgrade soil. Because of the complexities encountered with the test, in-situ and other laboratory tests would be desirable if a reliable correlation can be established. Relying on data from two-field test programs, correlation equations to predict resilient modulus of fine- and coarse-grain soils are proposed in this paper. Undisturbed samples are extracted from twelve in-service Mississippi subgrades, using a Shelby tube, and tested in a repeated triaxial machine for MR employing AASHTO TP46-94 protocol. The results suggest two comprehensive models—one for fine-grain and another for coarse-grain soil—in correlating laboratory MR to stress state. Model parameters are then correlated with soil index properties allowing the models to capture the effect of stress state, soil type, and soil properties. For model verification, an independent set of data from nine different Mississippi subgrades is used, observing good comparison between actual and predicted moduli.