Effect of clay invasion on shear behavior and dilatancy of unbound aggregate subbase

Unbound aggregate subbase is occasionally fouled by the invading or pumping of fine subgrade soils, and evaluation of clay invasion on shear and dilative behaviors become practically valuable. This paper presents an experimental investigation of the effect of clay invasion on shear and dilative behavior of a tested granite aggregate, used as subbase fill. To deepen the understanding of dilation, the large-scale triaxial tests (TX) tests were conducted on aggregate–clay mixtures in saturated conditions. The invasion of clay into unbound aggregate subbase leads to decreasing peak strength and critical strength, with a 20–30% strength loss. Both the clay inclusion and the increasing confining pressure decrease the volumetric strain in the form of dilation suppression. For the mixtures, the linear relationship was observed between the constant parameter of dilatancy angle and shear stress ratio. A hyperbolic model was proposed for the dilation rate and shear stress ratio, and the parameters, a, b, k, were identified. Results show a good agreement between the experimental diagrams and the modeling trends. The findings would benefit the application of unbound aggregate materials in pavements.