Elastoplastic framework of relationships between CBR and Young’s modulus for granular material

Abstract

CBR testing, developed before the Second World War, is still the most commonly used experimental procedure for pavement design. Today, CBR tests are correlated with the resilient modulus, which is a key parameter in current mechanistic pavement design methods. However, results of these correlations have been scattered, indicating that other variables are ignored. The purpose of this study is to show how the value of the CBR test is a function of other variables such as particle size and shape, crushing, and the elastic behaviour of the material. These variables were evaluated through FEM (Finite Element Method) simulations while varying several geotechnical parameters known in practical geotechnics. These FEMs include a linear elastic model and a failure criterion (elastoplastic model) and were prepared for granular soils under drained conditions. The evaluations show that the CBR not only depends on Young’s modulus (the parameter commonly used to correlate with the CBR), but also appears to depend on compressibility due to particle crushing. This appears to be a predominant parameter that can affect the CBR in the elastic domain as much as Young’s modulus does. Finally, this paper provides insights that improve the understanding of variables leading to high or low CBR values for granular materials. In addition, FEM simulations have been compared to the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) and other methodologies used in road geotechnics.