Effect of Cyclic True-Triaxial Boundary Types on Stress-Strain Behavior of Unbound Material

The stiffness characteristics of pavement foundation layers are one of the major factors affecting long-term pavement performance. Resilient modulus (MR) is a key parameter to evaluate the behavior of geomaterials when they are subjected to continuous traffic loads. Therefore, a reliable characterization of the stress-strain behavior of geomaterials through laboratory tests is crucial for pavement design. In this study, a cyclic true-triaxial device that has the capability of conducting MR tests on prismatic specimens with mixed rigid and flexible and six rigid boundary conditions was used to determine the effects of boundary type and stress history on the stiffness characteristics of an unbound geomaterial. The test results revealed that the rigid boundary condition yielded higher MR in both vertical and horizontal directions regardless of the applied stress history. The anisotropy ratios for mixed-type and rigid boundary conditions were determined as 0.09 to 0.21 and 0.05 to 0.41, respectively.