Several research studies have shown that unbound pavement layers exhibit anisotropic properties. Anisotropy is caused by the preferred orientation of the aggregate, to which both the shape characteristics of the aggregate and the compaction force itself contribute. The result is that unbound pavement layers have higher stiffness in the vertical direction than in the horizontal direction. The efÞcacy of using anisotropic properties to represent unbound layers is demonstrated by comparing pavement surface deßection measurements under wheel loads to Þnite element predictions based on models that incorporate isotropic and anisotropic properties for the unbound base and subbase layers. The surface deßections in the ßexible pavements of the AASHO road test were selected for this comparison because the AASHO road test is such a widely used database and because of the tight control of trafÞc, pavement cross sections, and material quality at the road test. The paper also analyzes the inßuence of characterizing pavement layers as isotropic and anisotropic on the predictions of fatigue and permanent deformation performance of ßexible pavements using the recently developed National Cooperative Highway Research Program 1-37A models. The results show that the anisotropic behavior of pavement layers explains part of the shift and calibration factors used to relate laboratory measurements to Þeld performance.
有意思吗诸位,那话都不通顺,就别往过粘了行吗?