Resilient Modulus Modeling of Unsaturated Subgrade Soils with Matric Suction Control

Publisher's full text
Farhad Salour
Claudia E. Zapata

Stiffness of pavement subgrade materials that is commonly determined by the resilient modulus parameter is an important component in the mechanistic design of flexible pavement structures. Environmental effects such as seasonal variations in pavement moisture content can considerably influence this material property which should be properly consideredin any realistic pavement design. The seasonal changes in moisture condition affects the stress state in the subgrade due to changes in the matric suction which is an important stress state variable in unsaturated soil mechanics.

In this study, a modified test procedure and apredictive resilient modulus model that takes into account the subgrade soil matric suction asa stress state variable is presented. Two different silty sand subgrade materials were tested inunsaturated conditions using a series of Repeated Load Triaxial (RLT) tests. The tests wereperformed under various matric suctions (moisture contents) to enhance the understandingof its effect on the resilient modulus. The results showed a considerable influence of the moisturecontent (matric suction) on the subgrade resilient modulus. The resilient modulus datatogether with the suction measurements were used and a set of parameters for the enhancedpredictive model were developed. This model accounts for seasonal variation of subgradematerial stiffness by incorporating suction as a stress state variable.

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