Techniques typically used in mechanistic analyses to characterize the behavior of unbound granular materials in a flexible pavement often predict stress conditions exceeding the material's static strength. Some pavement analysis tools such as ILLI-PAVE attempt to adjust predicted stresses in unbound layers so that they do not violate the Mohr-Coulomb failure envelope. However, the adjusted stresses are used only to calculate the resilient modulus to be used in the next iteration of the model, resulting in "final" stresses that are questionable and that frequently exceed the material's strength. Laboratory resilient modulus tests were conducted on granular at stress states exceeding the material's static shear strengths. Based on the data obtained, a material model for unbound granular material was developed that is a modification of the commonly used "k-theta-n" model for unbound granular materials. In addition, an advantage of the modified model is the ability to analyze the structural effects of granular materials having different shear strength characteristics. (A)
Abstract