Investigation of Dilatancy Effects on Asphalt Interface Shear Strength

Dilatancy is described as the shear-induced volume change in granular materials. An inclined shear test was used in this study to measure dilatancy on double layer asphalt specimens, where, due to the configuration of the device, dilatancy cannot be inhibited. Under monotonic loading conditions, three angles of 30°–45°–60° between the specimen axle and the horizontal were considered, so as to set different ratios between normal and shear force. A guillotine shear test was used to compare allowed and inhibited dilatancy at different levels of applied normal stress. The dilatancy angle ψ and the dilatancy speed were introduced as useful parameters to characterize the phenomenon. The results proved that, by inhibiting dilatancy, the interface shear strength increases of a constant amount regardless of the applied normal pressure. Moreover, the comparison of the test outcomes between the two devices highlighted the non-contemporaneity between the dilatancy speed peak and the shear stress peak in the inclined shear test. It can be attributed to the fact that the volumetric expansion of the specimen is countered by the normal stress, which increases proportionally to the shear stress during the test.