Evaluation of Pavement Base and Subgrade Material Properties and Test Procedures (1335-2)

The objective of this research was to develop simpler and less expensive procedures for characterizing the resilient properties, K1 to K3; the strength parameters, cohesion, C; and angle of internal friction, [phi], of base and subgrade materials. Researchers accomplished this by developing prediction equations which use easy to obtain soil properties and by evaluating a modified Texas biaxial test procedure which can be used to determine both the strength and resilient properties of pavement materials. Researchers tested five subgrade soils, i.e., sand, lean clay, fat clay, silt, and sandy gravel, and four base materials, i.e., crushed limestone, caliche, shellbase, and iron ore gravel, according to Texas specifications to obtain a database of material properties for developing the prediction equations. In developing this database, the strength parameters, C, and [phi], of the Mohr-Coulomb yield criterion, were obtained from standard Texas biaxial tests. For the resilient properties, compressive creep and recovery tests were run using AASHTO T-274 as a guide, to obtain the resilient moduli and Poisson's ratios of the materials tested at different stress states and moisture contents. The standard Texas biaxial test procedure, TEX-117-E, was modified to include a creep and recovery cycle before the test sample is loaded monotonically to failure. This loading sequence produced test data that allowed the estimation of the K1 to K3 resilient properties in addition to the strength parameters, C, and [phi]. The strength and resilient parameters obtained from the modified Texas biaxial test were compared to those obtained from the standard Texas biaxial test and the compressive creep and recovery test. Researchers document the results of these comparisons, as well as the development of the equations for predicting the strength and resilient parameters of base and subgrade materials, in this report.