Improvements to Pavement Subgrade Strain Criterion

Abstract

Relationships between maximum allowable elastic strain on the subgrade and number of load repetitions have been used extensively in pavement design procedures. Their development is reviewed to allow a proper perspective on their correct use and as a background for describing improvements which take account of the differing deformation resistance offered by various asphalt mixtures. These improvements are derived from both field data and the results of an extensive testing program during the last four years at the University of Nottingham using repeated load triaxial tests. A continuously graded dense bitumen macadam base can carry more than 1‐1/2 times the number of load applications before developing the same limiting rut depth as a gap graded hot rolled asphalt of equal elastic stiffness. Factors on the design life against permanent deformation are given for four typical materials for use in conjunction with the subgrade strain criterion.