EFFECTIVE MODULI AND STRESS DEPENDENCE OF PAVEMENT MATERIALS AS MEASURED IN SOME HEAVY-VEHICLE SIMULATOR TESTS

The purpose of this paper is to describe a method for determining field-effective moduli of pavement materials and to demonstrate stress dependence, especially of unbound materials. The effective moduli were determined from resilient deflections measured with a multidepth deflectometer at different depths within pavement structures. The results of measurements on four structures are reported. These structures cover light, unbound pavements to stronger inverted structures. The heavy-vehicle simulator was used to determine the moduli at different wheel loads and at various stages of trafficking. The ELSYM5 linear elastic-layered program together with the measured depth deflections were used in an iteration technique to determine effective moduli. The stress-stiffening behavior of granular materials and the stress-softening behavior of subgrade materials were clearly demonstrated. The constants in the models normally used to describe the behavior of these materials could be determined from the field results at various stages of trafficking and under changing moisture conditions. Laboratory and field values of stress-dependent moduli for granular materials were compared and a shift factor was determined. The effect of subgrade support on the effective moduli was also illustrated. (Author)