Elastoplastic framework of relationships between CBR and Young’s modulus for fine grained materials

Abstract

Abstract Despite its limitations, the California Bearing Ratio (CBR) test is currently the most commonly used method for measuring the quality of road materials. The CBR measures the resistance of a soil to penetration by a punch. The CBR index consists of the ratios between stresses measured at certain penetration levels in the tested material and the stress in a standard material at the same penetration level. Several studies have tried to correlate CBR test results with the resilient modulus because the resilient modulus is a key parameter in modern methods of mechanistic pavement design and analysis. Nevertheless, the high degree of scatter of these correlations indicates a need for theoretical analysis of the effects of the geotechnical variables that go into producing CBR measurements. The purpose of this study is to show how the California Bearing Ratio is a function of other variables including compaction energy, permeability, and the elastic behavior of a material. These variables were evaluated through FEM (Finite Element Method) simulations while several geotechnical parameters known in practical geotechnics were varied. These FEMs were prepared for fine soils and include an elastoplastic model. The evaluation shows that the CBR depends not only on Young’s modulus (a parameter commonly correlated with the CBR), but also appears to depend on compressibility due to compaction energy. In addition, the CBR is a function of permeability as indicated by differences found between drained and undrained conditions. After those evaluations, simulations were compared with pavement design guides, international standards and international recommendations.