Performance Evaluation of Backcalculation Algorithms Through Three-Dimensional Finite-Element Modeling of Pavement Structures

Abstract

Currently, the only means of assessing the performance of a backcalculation algorithm is to compare its results with the values obtained through laboratory measurements of core samples. Discrepancies are attributed to the inability of replicating in laboratory tests the same consolidation and stress conditions encountered in the field. In this paper, an explicit three-dimensional (3D) finite-element model (FEM) is used to back-calculate the layer moduli of rigid, flexible, and composite pavement structures. The modeling approach accounts for the dynamic nature of the falling weight deflectometer (FWD) load, friction at pavement-layer interfaces, and the 3D geometrical characteristics of the pavement structure. The FWD-measured and FEM-generated deflection basins are matched by adjusting the values of layer moduli used in the FEM. The backcalculated moduli using 3D FEM are compared with the results obtained from three backcalculation programs: MODCOMP, MODULUS, and EVERCALC. The results indicate that the three programs have an excellent capability of predicting the FEM-generated subgrade modulus values for flexible, composite, and rigid pavements provided that a correction factor is used. A correction factor for backcalculated subgrade modulus is estimated for each program and pavement type. The mechanistically evaluated correction factors were found to be in close agreement with the experience-based values recommended for flexible and rigid pavements in the American Association of State Highway Officials pavement design guide.