Study of In Situ Pavement Material Properties Determined from FWD Testing

The Vermont Agency of Transportation (Agency) developed pavement design procedures patterned after the American Association of State Highway and Transportation Officials (AASHTO) pavement design model described in the AASHTO 1993 pavement design guide (guide). A consequence of using the structural number approach to pavement design is the need for structural layer coefficients (ai) to characterize the component materials of the pavement structure. The agency has developed and tested a method for determining layer coefficients using a falling weight deflectometer (FWD), and the resulting layer coefficients are representative of the in situ behavior of the pavement materials. The agency found layer coefficients determined for unbound subbases to be reasonable, while layer coefficients estimated for asphalt cement concrete materials were generally 25–35% higher than AASHTO’s implied maximum of 0.44. However, a statistical analysis indicates considerable support for the predictive qualities of FWD derived layer coefficients to approximate layer coefficients simulated from the in situ conditions expected to prevail in the final pavement structure.