Subgrade soil index properties to estimate resilient modulus for pavement design

Abstract

Mechanistic pavement design procedures based on elastic layer theory require characterization of each material in the pavement structure in terms of elastic 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 M R for fine- and coarse-grained (sandy) soils are proposed in this paper. Twelve test sections reflecting a range of typical subgrade soil materials of Mississippi are selected and tested. Undisturbed samples are extracted and tested in a repeated triaxial machine for M R, employing AASHTO TP46-94 protocol. Other soil index properties are also determined, facilitating soil classification according to AASHTO procedure. The results suggest two relations—one for fine-grain and another for coarse-grained (sandy) soil—in correlating laboratory M R to soil index properties. These models include the most relevant factors that influence M R values. For model verification, an independent set of data is used, observing good comparison between actual and predicted moduli. These models with the soil properties included could be used in levels 2 and 3 in the new 2002 AASHTO Design Guide substituting other empirical correlations (level 2) and the use of modulus typical values (level 3).