Dr. Yuqing Zhang is a Lecturer (Assistant Professor) in Highway Engineering and the Deputy Director of Aston Institute of Materials Research (AIMR) at Aston University in Birmingham, UK. He earned his Bachelor and Master’s Degrees at Southeast University in Nanjing, and Ph.D. Degree at Texas A&M University. Dr Zhang moved to the UK in 2015 and is now leading an infrastructural material research group at AIMR. His research is focused on mechanics based multiscale and multiphysics modelling of pav

Abstract:

Unbound granular base (UGB) has a cross-anisotropic and nonlinear (stress-dependent) modulus with a plastic behaviour. Existing UGB models addressnonlinear cross-anisotropy and plasticity separately. This study presents a coupled nonlinear cross-anisotropic elastoplastic (NAEP) constitutive model for the UGB and implements it in a weak form equation-based FEM. No material subroutine is needed to address the model’s circular dependence. The NAEP model was calibrated by triaxial resilient modulus and strength tests and validated by a large-scale soil-tank pavement structural test. It is found that the NAEP model is valid and effective in predicting the UGB responses in flexible pavements. The model predicted less horizontal tensile stresses at the base bottom and introduced compressive stresses in the middle and top of the base course. This is caused by an increasing confinement resulting from a horizontal plastic dilation in the base course, which cannot be modelled without considering plasticity. Compared to a nonlinear anisotropic elastic (NAE) model, the NAEP model predicted the same tensile strain at asphalt layer bottom, a higher base modulus and a higher subgrade compressive strain. Thus the NAE model can predict the same fatigue life as the NAEP model, but may riskily under-predict the rutting damage.