Estimation of level of anisotropy in unbound granular layers considering aggregate physical properties

A simple procedure is developed to account for the effects of aggregate physical properties (gradation and shape characteristics) in predicting the cross-anisotropic properties of unbound granular layers. Variable confining pressure repeated triaxial tests were performed on six aggregate sources with three different gradations (coarse, intermediate and fine) and three different moisture contents (wet, optimum and dry). The experimental results were analysed to determine the parameters of a cross-anisotropic non-linear elastic model. Image analysis techniques were utilized to measure aggregate shape characteristics (form, angularity and texture). The distributions of particle size and shape characteristics of the six aggregates were fitted using a non-linear regression model. The cross-anisotropic model parameters of unbound granular bases were in turn related to the coefficients of the regression model. The analysis results indicate that aggregate physical properties significantly affect the anisotropic resilient behaviour of unbound granular bases, and this anisotropic resilient behaviour has substantial effect on the critical pavement responses. Thus, it is valuable to approximate the degree of cross-anisotropy in unbound aggregates based on aggregate physical properties in order to adequately analyse and design pavements.