Flexible Pavement Evaluation Using Hertz Theory

Hertz's theory of the deflection of an elastic plate on a fluid subgrade, which was the basis for Westergaard's analysis of concrete pavements, is shown to be applicable to flexible pavement evaluation. Graphs are presented enabling the interpretation of deflection bowl measurements for both the vibratory Road Rater and the Benkelman Beam in terms of the characteristic length, l, of the flexible pavement. The load required to cause a unit deflection of the pavement surface, referred to as pavement stiffness, is examined in terms of the size of the loaded area, the pavement flexural rigidity, and the coefficient of subgrade reaction. The required pavement stiffness is shown to increase for multiple wheel gears with increasing pavement characteristic length. Test data are presented for both conventional flexible and full depth asphaltic concrete pavements on clay subgrades using both the Road Rater and Benkelman Beam.