A three dimensional (3D) finite element (FE) model has been developed to predict pavement responses to vehicular loading. The model incorporates measured tire-pavement contact stresses, continuous moving-wheel loading, and HMA viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pavement response from accelerated loading. Two tire configurations (dual-tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152mm, 254mm and 420mm) were utilized in both FE modeling and accelerated loading tests. The predicted and calculated strain responses at the bottom of HMA were in agreement. The study had several conclusions. Most importantly, it shows that vertical shear strain in the upper 76-100mm of the pavement surface is critical for thick pavement and is influenced by the 3D tire-pavement contact stresses under each tire rib. However, the tensile strain at the bottom of HMA is mainly affected by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. It is important to note that top-down cracking could result from the local vertical shear strain in the upper 25mm of the HMA where the effect of tire-pavement tangential stresses are the highest. Additionally, the study concluded that wide-base tires cause higher longitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses.
Abstract