Model for Seasonal Variation of Resilient Modulus in Silty Sand Subgrade Soil: Evaluation with Falling Weight Deflectometer

Abstract

One of the main input parameters in the mechanistic design and analysis of pavement systems, the stiffness of unbound pavement material usually is moisture dependent. As a result, most unbound pavement layers exhibit seasonal variations in stiffness as the pavement moisture content changes over the year. Any realistic pavement design should take this variation into account. In unbound material with a high fines content, a change in moisture content can change the stress state because of suction effects. An enhanced predictive resilient modulus model is presented to account for seasonal variation by means of suction measurement. A silty sand subgrade soil was tested with a modified repeated load triaxial system under different moisture (suction) conditions, and a set of resilient modulus model regression parameters was determined. The capability of the model to capture seasonal variation in moisture content was evaluated further with field data. A series of falling weight deflectometer (FWD) tests with multilevel loads was conducted on an instrumented pavement structure in which the moisture content of the subgrade was changed by manipulating the pavement drainage condition. The resilient modulus values obtained from the model were compared with backcalculated stiffness data obtained from FWD tests conducted under different moisture conditions. Overall, agreement was good between the laboratory-based resilient modulus values and the backcalculated stiffness. The resilient modulus–suction model could efficiently capture the moisture content effects.