Influence of Grain Gradation on Permanent Strain of Unbound Granular Materials under Low Confining Pressure and High-Cycle Loading

Abstract

Unbound granular materials (UGMs) are widely used as road-base and subbase materials for bearing traffic loading. Significant road settlements can be caused by cyclic traffic loading after several years of operation. To investigate the settlements of base and subbase induced by traffic loading, a series of large-scale cyclic triaxial tests were conducted under low-amplitude and high-cycle loading. Special attention was paid to the effects of the grain gradation on the strain accumulation of UGMs under cyclic loading. Test results showed that the gradation had a considerable effect on the accumulated deformation of UGMs under various cyclic loadings. Based on the experimental results, an improved high-cycle accumulation (HCA) model, incorporating a new function to consider the influence of grain gradation, was proposed. Good agreement was observed between the results predicted by the improved HCA model and the validation-test results.