Deformation characteristics of granular materials subjected to rapid, repetitive loading

Abstract

The engineering behavior of soils and aggregates is a function of their basic properties and the environment to which they are subjected. In pavement design the effect of repeated loading is in important environmental condition which has received little attention, especially for granular materials. This report present results showing the influence of repetitive triaxial stressing on the deformation of granular (flexible base course) materials. The materials examined were a) hard rounded material (gravel), b) hard angular material manufactured by crushing oversized pieces of the gravel, and c) a soft crushed limestone. Each material -- except the soft -- was tested at three separate gradations representing the coarse, medium and fine ranges allowed by Texas Highway Department specifications for such materials. The total strain characteristics of the materials were quantitatively related to the applied stresses and number of stress repetitions. It was shown that the behavior under repetitive stresses was not closely related to static shear strengths as determined by the Texas triaxial method. Rebound strains could only be expressed qualitatively. Under repetitive stressing the rounded material, which ranked lowest in static shear tests, was at least equivalent to the angular material for the stress range expected in roadways; both were superior to the soft material. It is believed that the relative densities of the respective materials influenced their behavior more than particle shape or hardness. Finally, recommendations were made for improving equipment and testing procedures which should simplify analysis of results and reduce experimental error in future investigations.