Evolution of the strain localization and shear-zone internal structure in the granular material: Insights from ring-shear experiments

Shear zones are commonly observed in natural faults, landslides, and laboratory experiments involving granular materials. Gaining insight into the evolution of shear zones in these materials is essential for understanding the mechanics of faults and landslides, yet this process remains insufficiently understood. To address this, we conducted a series of ring-shear experiments to study the development of strain localization and the internal structure of shear zones in both cohesive and non-cohesive granular materials. Using high-resolution X-ray computed tomography (CT), we quantitatively analyzed shear-zone structures, including particle shapes, orientations, and grain-size distributions, at various levels of shear strain. Our results reveal that with increasing shear displacement, larger particles within the shear zones become progressively rounded, though without a preferred orientation. Additionally, wear and attrition processes generate a significant number of nanoparticles within the shear zones. Fine-particle layers composed of these nanoparticles were observed to form along the edges of the shear zones as shear localization developed, suggesting a transition of the shear process from a distributed zone to a more defined interface. These findings provide insights into the evolution of shear zones in granular materials, offering a deeper understanding of the mechanics underlying fault and landslide dynamics.