Characterising the elastic behaviour of fine-grained subgrade soils under traffic loading

Resilient modulus is a measure of the elastic behaviour of subgrade soil under traffic loading. The design thickness of a pavement structure and its predicted performance are highly dependent on subgrade modulus. Characterisation of subgrade resilient modulus involves conducting advanced repeated loading triaxial testing that requires special equipment and technical experience that are not available in many soil laboratories. The objectives of this paper were to characterise the resilient modulus of typical fine-grained subgrade soils and develop design inputs for the Mechanistic-Empirical Pavement Design Guide. The resilient modulus of subgrade soil samples was tested at different levels of moisture content. Results of the laboratory testing were used to develop prediction models for resilient modulus as function of physical properties of the subgrade soil and stress state. The proposed models were compared to those developed under the Long-Term Pavement Performance programme. The results showed that the proposed models provided more reliable predictions with lower root mean square error.