Evolution of particle breakage during cyclic shear of sand

The evolution of particle breakage in sand with different mineralogy under cyclic shear loading is explored. The work focuses on the impact of factors such as the cyclic stress ratio (CSR), confining pressure, amplitude of shear stress and number of cycles. Direct shear tests were carried out at increasing stress levels and numbers of cycles. Specimens were recovered after each test and subjected to dynamic image analysis (DIA), which permitted capturing not only changes in the particle size distribution (PSD) but also evolution of particle shapes for approximately 4% of all particles tested at a fine scale. Detailed analysis of the PSD curve combined with an analysis of the evolution of particle shapes, demonstrates how soil gradation evolves during cyclic loading and how this impacts the mechanical behavior of sand. The study presents a novel framework for predicting particle breakage in sands subjected to cyclic loading using readily available stress–strain data, eliminating the need for complex and costly fine-scale particle size analyses. The method adapts the existing Loading Intensity (L_I) framework, incorporating an efficiency factor that accounts for the diminishing effect of cyclic loading as the number of cycles and cyclic stress ratio increase. A strong correlation was established between the Particle Partition Potential (P₃) and Hardin's Breakage Index (Br), enabling the prediction of particle breakage with generally small errors (< 2%) and remarkable accuracy at higher breakage levels. This framework offers a reliable and practical tool for assessing soil degradation under cyclic loading.

Graphical Abstract