Significance of Subgrade Damping on Falling Weight Deflectometer Test

Falling Weight Deflectometer (FWD) produces pavement responses by a falling mass drop to evaluate structural parameters of the pavement. A reliable simulation model is helpful to calibrate the apparatus as well as the backcalculation programs. The key points in the finite element simulation of FWD tests were studied including model size, boundary conditions, and analysis time increment. The subgrade in the finite element model was formulated with springs of stiffness coefficient of subgrade and dashpots of the derived damping values. The minimum model size is concluded to be 6 times the radius of relative stiffness to avoid boundary cut-off error. A rigorous procedure is proposed to derive subgrade reaction and damping for various types of subgrade soil. Subgrade damping plays an important role in simulations of FWD test. Backcalculation programs without subgrade damping may over-predict structural condition of pavements.