Numerical modeling of geogrid-reinforced flexible pavement and corresponding validation using large-scale tank test

This study aimed to develop a finite element model to simulate the geogrid-reinforced flexible pavement structure by taking into account the lateral confinement effect of geogrid layer, the interaction between geogrid and aggregate/soil, and the nonlinear cross-anisotropy of geogrid-reinforced unbound granular material (UGM). First, an analytical model was proposed to quantify the effect of the lateral confinement of geogrid layer on the resilient modulus of UGM. By comparing to the laboratory triaxial test results, the developed analytical model was proven to accurately predict the resilient modulus of geogrid-reinforced UGM. Second, the Goodman interface element model was used to characterize the contact behavior of geogrid-aggregate/soil interface. In order to simulate the nonlinear cross-anisotropic behavior of geogrid-reinforced UGM, a user-defined material (UMAT) subroutine was programmed using the secant modulus approach. The accuracy of the developed UMAT was verified by comparing the numerical simulation results to the analytical solutions in a virtual triaxial test. Two pairs of geogrid-reinforced and unreinforced pavement models were analyzed in this study. It was found that the geogrid reinforcement is effective in mitigating the rutting damage of base course and subgrade, but cannot significantly extend the fatigue life of flexible pavement. The geogrid reinforced in the middle of the base course is better at reducing the rutting damage of base course than that placed at the base/subgrade interface. However, the geogrid reinforcement is much more effective in reducing the rutting damage of the subgrade when it is placed at the bottom of the base course. A comprehensive large-scale tank (LST) testing program was designed to record the critical pavement responses, including the surface deflection, the tensile strain at the bottom of the asphalt concrete, and the vertical stresses in base course and subgrade. The developed geogrid-reinforced and unreinforced finite element models were finally validated by comparing the model predictions with those measurements from the LST test.