Characterisation and modelling of subgrade resilient modulus for pavement structural design in Egypt

In Egypt, estimation of subgrade resilient modulus (MR) for the structural pavement design is based on empirical correlation with California Bearing Ratio (CBR) adopted from literature. Thus, this study aims at verifying if this correlation is still valid for different Egyptian subgrade soils, otherwise calibration is warranted. A comprehensive experimental program is conducted on local sixteen subgrade materials. The testing program includes MR, CBR, and index soil properties such as gradation, Atterberg limits, Proctor compaction characteristics, and shear strength parameters. Four simple regression models correlating MR and CBR values are developed for local subgrade materials based on the anticipated field stresses under two different traffic loading conditions pertinent to Egypt. The proposed correlations yield more accurate MR values for the local materials and traffic loading conditions. Consequently, this is expected to contribute to a realistic pavement structural design, and hence better pavement performance over the service life.