Performance prediction of pavements requires the proper assessment of permanent deformations and fatigue of the structure under applied traffic loads. Of particular importance in this case is whether a given pavement structure will experience progressive accumulation of plastic strains or whether the increase in plastic strains will cease to occur, thereby leading to a stable response or shakedown. A numerical method for predicting shakedown of pavements in developed in this paper. The proposed numerical approach involves discretization of the pavement structure using the finite element method. An iterative scheme is implemented that satisfies shakedown conditions, together with the nonlinear resilient load-deformation characteristicsof the granular and subgrade layers. Convergence is attained when alimiting or shakedown load could be determined for which the stress-resilient strain relations are satisfied, and a time-independent residual stress field exists for which equilibrium conditions, boundary conditions, and yield conditions (i.E., Mohr-coulomb yield criterion in this case) are fulfilled. The proposed method is applied to study the shakedown behavior of pavements with granular layers. Specifically, the influence of strength of the granular layer in terms of cohesion and friction is investigated. In this case, the results of a limited number of laboratory triaxial tests showing the effect of aggregate interlock, percent fines, and compaction water content on the cohesion and friction parameters are used. The influence of other factors (such as initial stresses induced by compaction and overburden pressure) is illustrated. Shakedown behavior is then compared with fatigue of the surface layer in an attempt to develop a better understanding of pavement performance. This paper appears in transportation research record no. 1227, Rigid and flexible pavement design and analysis: unbound granular materials, tire pressures, backcalculation, and design methods.
Abstract