Acknowledgment

This report has been prepared with funds provided by the United States Department of Transportation to the Mountain-Plains Consortium (MPC).  The MPC member universities include North Dakota State University, Colorado State University, University of Wyoming, and Utah State University.

The authors would like to express their appreciation to Mr. Benjamin Adkinson, Wyoming DOT Laboratory Technician for completing the laboratory tests and to Dr. Richard Anderson-Sprecher for technical assistance in the statistical analyses.

Disclaimer

The contents of this report reflect the views and ideas of the authors, who are responsible for the facts and the accuracy of the information presented herein.  This document is disseminated under the sponsorship of the Department of Transportation, University Transportation Centers Program, in the interest of information exchange.  The U.S. Government assumes no liability for the contents or use thereof.

Preface

This report describes a study jointly conducted by the University of Wyoming and the Wyoming Department of Transportation to better understand how selecting a M_R value influences the thickness of an asphalt overlay pavement. The objectives of this study were to:  1) investigate the importance of several fundamental soil properties (water content, plasticity index, liquid limit, group index) on selecting a design subgrade resilient modulus value for cohesive soils; 2) define the actual relationship (correction factor) between back calculated and laboratory based M_R values for typical cohesive subgrade soils in Wyoming; 3) compare actual subgrade field deviator stresses to the deviator stress assumed in determining a design M_R value from laboratory testing; and 4) determine the effect of selecting a M_R value on the design overlay thicknesses for typical pavement sections in Wyoming.  The data analysis resulted in several important conclusions about factors that influence the determination of the subgrade resilient modulus value and how this value affects the final design overlay thickness for a given pavement section.