Dynamic analysis of thin asphalt pavements by using cross-anisotropic stress-dependent properties for granular layer

A three-dimensional (3-D) finite element (FE) model was developed to investigate the dynamic responses of thin, flexible pavement under impulsive loading similar to a falling weight deflectometer test. The FE model simulated the hot-mix asphalt (HMA) surface layer as a linear viscoelastic material and considered the cross-anisotropic stress dependent modulus for the unbound base layer. Implicit dynamic analysis was used to consider the effect of inertia on pavement structural responses. Using two thinpavement structures of different HMA layer thicknesses, 76 and 127 mm, the study analyzed the effects of cross-anisotropic stress-dependent aggregate base modulus and dynamic analysis on pavement responses, including surface deflection, tensile strain at the bottom of the HMA layer, deviator stress in the base layer, and compressive strain on top of the subgrade. Results showed that use of the cross-anisotropic stress-dependent modulus for the unbound base layer resulted in greater predicted pavement responses and, hence, less estimated pavement life for rutting and fatigue cracking. It was found that as the thickness of HMA surface layer or the ratio of horizontal modulus to vertical modulus decreases, the effects of stress dependency and cross anisotropy become more significant. Analysis-predicted surface deflections were compared to field-measured values and they were in agreement when the stress dependency and cross anisotropy of the base layer and subgrade were considered.