Significance of subgrade damping on vehicle-pavement interactions

The falling weight deflectometer (FWD) producespavement responses by a falling massdrop to evaluate structural parameters of the pavement. A reliablesimulation model is helpfulto calibrate the apparatus as well as the backcalculation programs. The key points in the finite element simulationof FWD tests were studied including model size, boundary conditions, andanalysis 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. It was concluded that at least sixtimes the radius of relative stiffness is required to avoid boundary cut-off error. A rigorous procedureis presented to derive subgrade reaction and damping for various types of subgrade soil. Subgrade damping plays an important role in simulations of the FWD test. Backcalculation programs without subgrade damping may over-predict structural condition of pavements.