Validation of theoretical models through measured pavement response

Most models for structural evaluation of pavements are of the analytical-empirical type. An analytical model, derived from solid mechanics, is used to calculate stresses or strains at critical positions, and these stresses or strains are then used with empirical relationships to predict pavement performance.

The analytical models are based on a number of simplifications with respect to reality and must be verified experimentally.Different pressure gauges were installed in a sand, assumed to be a semi-infinite halfspace. The surface of the sand was loaded by a Falling Weight Deflectometer (FWD) at different lateral positions with respect to the gauges.

An integration of the stresses measured at the plane of the gauges showed that the total load recorded by the gauges was close to the loade imposed by the FWD, cofirming the reliability of the gauges. The theoretical stress calculated using continuum mechanics was quite different from the measured stress, the peak theoretical value being only half of the measured value.On an instrumented pavement structure in the Danish Road Testing Machine, deflections were measured at the surface of the pavement under FWD loading.

Different analytical models were then used to derive the elastic parameters of the pavement layeres, that would produce deflections matching the measured deflections. Stresses and strains were then calculated at the position of the gauges and compared to the measured values. It was found that all analytical models would predict the tensile strain at the bottom of the asphalt layer reasonably well, but that the vertical strain at the top of the subgrade could only be predicted with some degree of accuracy if the subgrade was treated as a non-linear elastic material.