An Assessment of the In Situ Test Technologies for Estimating the Resilient Modulus of Subgrades

Resilient modulus of the subgrade is the most critical parameter in the structural design of a flexible pavement. To estimate the resilient modulus, repeated cyclic loading tests are usually employed. Due to the difficulties associated with cyclic load testing, approximate methods are often employed to determine the resilient modulus. In the current study, this factor is evaluated using empirical relationships with elastic modulus by conducting experimental study. A full scale evaluation of the subgrade performance was carried out in a test pit facility using few common in situ test technologies such as Soil Stiffness Gauge (SSG), Dynamic Cone Penetrometer (DCP) and Light Weight Falling Deflectometer (LWFD). Correlations have been developed for the estimation of resilient modulus from the elastic moduli measured from SSG, DCP and LWFD. The equations take into account the plasticity index, moisture content and dry density, so that the equation parameters represent the effect of soil type. The equations give consistency between the estimated resilient modulus and elastic modulus. These equations could serve as means to estimate the resilient modulus of the subgrade material in case of absence of the actual resilient modulus testing facility.