Effects of calcareous fine contents on the dynamic behavior of calcareous sand

To investigate the influence of calcareous fine contents ( FC ) on the dynamic behavior of calcareous sand, a series of undrained cyclic triaxial tests was performed on calcareous sand-fine mixtures with relative densities ( D r ) of 40% and 80%, incorporating FC values of 0%, 10%, 40%, 70%, and 100%. The study examined the effects of FC variation on dynamic strain accumulation, pore pressure generation and particle breakage under initial confining stresses ( σ ’ 3 ) of 50 kPa and 100 kPa. The experimental findings demonstrate that the number of cycles to failure ( N f ) decreases consistently with increasing FC under identical cyclic stress ratios ( CSR ). Specifically, the cyclic resistance ratio at 10 cycles ( CRR 10 ) decreases by up to 35.9% as FC increases from 0% to 70% at D r = 40%. Conversely, CRR 10 increases by approximately 25%–28% when D r rises from 40% to 80% across all tested FC values. Higher confinement ( σ ’ 3 = 100 kPa) reduces CRR 10 by 12.5% compared to σ ’ 3 = 50 kPa. Particle size analysis reveals that particle breakage, quantified by the relative breakage index ( B r ), is inversely correlated with FC , with B r values ranging from 0.71% to 0.87% depending on density and confinement. A power-law model effectively characterizes this attenuation effect. These findings elucidate the coupled mechanisms of fines-induced skeletal restructuring and particle crushing, providing critical parameters for the seismic design of calcareous sand foundations in coastal reclamation projects.