Developing Pavement Design Inputs for Fine-Grained Subgrade Soils in Manitoba

Resilient modulus is the primary design input for subgrade soil in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Characterization of subgrade resilient modulus requires instrumentation and technical experience that are not available in many soil testing Laboratories. The objective of this paper is to characterize the resilient modulus of typical subgrade soils available in Manitoba and develop design inputs for the MEPDG. The resilient modulus of fine-grained 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. A good agreement was found between measured resilient modulus and predicted values with the proposed models. The proposed models were compared to those developed under the Long Term Pavement Performance (LTPP) program. The results showed that the proposed models provided more reliable predictions with lower root mean square error.