A Best-Fit Rigid Pavement Back-Calculation Algorithm Using Site-Specific Deflections

This paper introduces an improved best-fit back-calculation technique based on deflection predictions obtained using finite element method (FEM) simulations (i.e., computer program EverFE), rather than generic theoretical deflection predictions. It is based on minimizing the squared error between falling weight deflectometer (FWD) measured deflections and FEM predicted deflections. It assumes that the modulus of the portland concrete is known and gives a closed-form solution for the reaction modulus k of the layers supporting the concrete slab. The results were compared to those obtained by the best-fit method used for the Long Term Pavement Performance (LTPP) program. The comparison was in terms of the mean absolute error between measured and estimated deflections. The latter were obtained using the slab reaction moduli back-calculated by the two methods. Comparing the back-calculated reaction moduli to the ones obtained by the plate loading test was less conclusive. Overall, the results support that the additional work required in modeling the slab and the loading configuration at the time FWD measurements are taken is worthwhile.