Sands Subjected to Repetitive Loading Cycles and Associated Granular Degradation

This study examines the load-deformation response of sands subjected to high- and low-stress cycles, i.e., both ends of the Wöhler’s fatigue curve. At high peak cyclic stress σf, the terminal void ratio decreases with σf due to crushing-dependent densification, and it can be smaller than emin when the peak stress approaches the yield stress σf→σy. When σf≪σy, the soil retains memory of the initial fabric even after a very large number of cycles, and the terminal void ratio correlates with the initial void ratio eo. Data show that the maximum change in relative density leads to simple strategies to estimate the maximum settlement for first-order engineering analyses. In agreement with Wöhler’s fatigue, tipping points in void ratio and stiffness trends occur at a small number of high-stress cycles or after a large number of small-stress cycles. During repetitive loading, sands stiffen with the number of cycles to reflect increased interparticle coordination following crushing, as well as contact flattening due to asperity breakage and fretting. The strong correlation between the resilient modulus Mr and the maximum shear modulus Gmax suggests the possible application of geophysical methods based on shear wave propagation to monitor geosystems subjected to repetitive loading cycles.