Laboratory resilient modulus tests were conducted on granular materials at stress states exceeding the materials' static shear strengths. The test results show that, above the static strength, the modulus decreases with increasing stress levels. These data were used to develop a characterization model that is a modification of the commonly used k-theta-n model. The modification consists of the addition of a stress ratio (stress/strength) parameter. The stress ratio model was used in the finite element program illi-pave to analyze typical flexible pavement sections. The analysis results are compared with similar analyses using the mohr-coulomb stress adjustment model normally used with illi-pave. The coparison shows that similar stress and strain patterns are predicted by both models but that the stresses predicted in the granular base by the stress ratio model appearto be more realistic. Also, the stress ratio model provides a meansfor analyzing the structural effects of granular materials having different shear strength characteristics. This paper appears in transportation research record no. 1227, Rigid and flexible pavement design and analysis: unbound granular materials, tire pressures, backcalculation, and design methods.
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