Determination of the resilient modulus under anisotropic stress conditions

The resilient modulus (MR) is one of the most important indicators of performance of geomaterials used in pavement foundation design, and since designed pavements often are not able to fulfill their service life, researchers have been led to evaluate the procedure of resilient modulus characterization of geomaterials used in pavement foundations systems. A preliminary study was conducted on a granular aggregate base material to determine whether conventional MR testing simulates actual stiffness behavior of these materials under actual traffic loads. The results of this study showed that the conventional testing equipment used to measure MR did not simulate actual field behavior of geomaterials because it fails to take into account anisotropic stress conditions, suggesting a need to produce more realistic experimental results by measuring and monitoring anisotropic stress conditions during testing. To respond to this need, a series of advanced MR tests were conducted using a custom designed and manufactured dynamic polyaxial testing system that enabled measurement of the resilient modulus of materials in both vertical and horizontal directions. It was observed that the geomaterial had different stiffness values at each direction and that the ratio of vertical stiffness to horizontal stiffnesses (modular ratios) can be defined to produce a better understanding of the performance of geomaterials used in pavement foundation design. It is believed that the findings of the study will enhance the long term performance and service life of designed pavement systems.