Cyclic Loading–Induced Volume Change in Angular and Rounded Gravel–Sand Mixtures in Centrifuge Models

Abstract This study examines the vertical strain behavior of gravel-dominated sand–gravel mixtures under cyclic loading using geotechnical centrifuge modeling. Two mixtures were tested, one comprising 80% angular crushed limestone gravel and 20% sand by mass, and the other comprising 80% rounded pea gravel and 20% sand, representing gravel-supported soil structures. Four models, prepared under loose and dense conditions, were subjected to sinusoidal shaking with a peak base acceleration of ∼ 0.37 g . Results showed that gravel particle shape strongly influences packing behavior, with angular gravel exhibiting higher maximum void ratios and a wider void ratio range than rounded gravel. Under drained monotonic loading, particle shape strongly influences global relative density, D r , with rounded gravel forming denser packs than angular gravel. However, this effect is much weaker in gravel skeleton relative density, D r g , which reflects only the gravel framework. Because D r g removes the influence of sand filling the voids, both mixtures start with nearly the same gravel skeleton, greatly reducing shape-related differences in vertical strain. Under cyclic loading, however, rounded mixtures generated higher excess pore pressure ratios, particularly at depth, despite comparable D r g values, due to their lower initial void ratios and sand migration. These conditions promoted upward flow and greater reconsolidation settlement. The findings highlight the critical influence of particle shape on the mechanical and hydraulic behaviors that govern the seismic response of coarse-grained soils, with important implications for foundation design and seismic site response analysis in gravel-dominated deposits.