Particle breakage is a key microscopic mechanism associated with damage accumulation, strength degradation, and geohazard evolution in granular systems subjected to cyclic loading. In this study, two-dimensional breakable photoelastic granular specimens were used to investigate the cumulative evolution of particle breakage and local structural responses under cyclic shear with different shear amplitudes and constant normal loading. A reproducible evolutionary process of particle breakage was experimentally captured and characterized. Although the onset time and growth rate of breakage vary markedly with shear amplitude, the systems consistently evolve toward a similar saturated breakage state, exhibiting a common plateau feature. The delayed onset of breakage indicates an amplitude-dependent incubation period, which can be interpreted as a cyclic-shear-driven activation process in which the granular assembly escapes from a metastable structural potential well. At the plateau stage, surviving intact particles are commonly surrounded by fragment-rich shell-like structures with multidirectional encirclement. Further displacement analysis suggests that the final steady state is jointly controlled by local fragment reorganization and non-affine particle motions. These findings reveal a multiscale pathway from incubation and activated breakage to saturation and stabilization, providing experimental insight into progressive damage evolution in crushable granular systems under long-term cyclic perturbations.

cyclic shear,non-affine motion,damage saturation,particle breakage,model granular media,fragment shell