Subgrade Evaluation Based on Theoretical Concepts

Report No: 70-R29

Published in 1971

About the report:

Evaluations of pavement soil subgrades for the purpose of design are mostly based on empirical methods such as the CBR, California soil resistance method, etc. The need for the application of theory and the evaluation of subgrade strength in terms of the modulus of elasticity in place of empirical methods is essential for rational design techniques. In this investigation, the maximum deflection of the pavement and the shape of the deflected basin were utilized to determine the modulus of elasticity of the subgrade. The shape of the deflected basin is defined by the word "spreadability", which is in turn defined as the average deflection as a percentage of the maximum deflection. An evaluation chart was developed. By means of this chart the modulus of elasticity of the subgrade can be determined if the maximum and four other deflections in the deflected basin are known. The same principle could be applied to develop a similar type of evaluation chart based on the information of the deflected basin collected by any other agency.

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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