<p>The origin and mechanism of silo failure represent challenging and prominent issues in current mechanical–structural coupling studies of granular matter. Continuum theory indicates that pressure distribution at the silo bottom is closely correlated with the packing height of granular materials. Consequently, recent research has predominantly focused on stress and porosity distribution differences arising from variations in packing height. Although this theory can adequately explain typical phenomena such as the silo effect under specific assumptions, the microscopic mechanisms and critical failure conditions remain incompletely understood. In this study, we conducted cyclic shear experiments on packing systems with different particle numbers using fixed-diameter cylindrical containers to measure their densifying behavior and mechanical response. The results demonstrate that when particle number undergoes minute variations (as small as 0.9%), leading to changes in geometrical packing structure and even particle layer configurations, not only do the densifying process and final state exhibit significant differences, but the friction torque on the top surface also displays distinct evolutionary patterns. Critical behavior emerges near the solid–liquid transition point, with a critical phase transition density of approximately 0.63. Fine adjustments in particle number can induce substantial changes in macroscopic mechanical properties, revealing the strong correlation between mechanical properties of granular matter and geometrical packing structure. Boundary confinement, particle number within the confinement, and their coupling effects render granular matter inappropriate for continuum theory treatment under certain circumstances. Therefore, the application of continuum theory to granular systems requires conditional consideration.</p>