Performance Prediction and Moisture Susceptibility of Anisotropic Foundations
Significant work has been done by the International Center for Aggregate Research (ICAR) to identify the effects of the anisotropic nature of compacted base courses on the stress, strain, and permanent deformation characteristics of pavement foundations. As continuation to this effort, current paper presents a mechanistic approach for determination of the variation of pore water pressure under a moving wheel load. This paper also presents a methodology as to evaluate the effect of pore water pressure on the anisotropic response of aggregate layers. Sixty-two aggregate systems were tested with varying fine contents and water contents. The aggregate blends were molded according to AASHTO T-180 and tested using state of the art equipment called the Rapid Triaxial Tester (RaTT) at three saturation levels to capture the moisture susceptibility of the aggregate systems. Variable Dynamic Confining Pressure (VDCP) stress paths were in turn used to determine the anisotropic material properties for each aggregate system. This approach shows that the external pressure applied on the surface of the pavement results in a reduction of the initial negative pore water pressure. The change in pore water pressure induced by traffic load for high fines content specimens at elevated saturation levels results in positive pore water pressure which is synonymous with more critical conditions for plastic deformation. Further analysis on the results shows the agreement between the proposed approach and the principle of change in pore water pressure presented by Henkel. Mohr-Coulomb yield function was employed as a performance indicator in this study. The stress sensitive and anisotropic material model showed that the hardening component of the stiffness in vertical direction at the centerline of the load and at the top of the aggregate base layer is approximately 20% smaller when the influence of pore water pressure is considered in the formulations.