A Method for Evaluating the Structural Performance of Subgrades and/or the Overlying Flexible Pavements

Report No: 70-R31

Published in 1971

About the report:

The structural evaluation of flexible pavement is now carried out mostly by deflection measuring devices such as the dynaflect or Benkelman beam. The object of this investigation was to determine whether the properties of the deflected basin measured by these devices on the pavement surfaces could enable evaluation of the subgrade and/or its overlying pavement separately. The properties of the deflected basin are defined by the maximum deflection and the spreadability, which is the average deflection expressed as a percentage of the maximum deflection. A theoretical analysis showed that these properties are a function of the modulus of elasticity of the subgrade, the average modulus of elasticity of the pavement over the subgrade, and the thickness index of the overlying pavement. A general chart was developed which correlates maximum deflection and spreadability with (i) the subgrade strength, (ii) the average pavement strength, and (iii) the thickness index of the pavement. This chart was tested for structural evaluations of the subgrade and/or its overlying pavement for satellite projects in Virginia. Ten typical examples of the satellite projects are given in the report and the change in their structural behavior with time is discussed.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


  • N. K. Vaswani 

Last updated: February 12, 2024

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