Abstract: To investigate the influence of particle breakage on the coefficient of earth pressure at rest (K₀) of coral sand, this study employs coral sands from the South China Sea for saturated K₀ consolidation tests under single-particle-size conditions. The particle breakage is quantified using the relative breakage rate, and the effects of particle size, relative density, and vertical stress on K₀ are systematically analyzed. The results demonstrate that: Under the action of high stress, particle breakage weakens the transmission ability of lateral stress, resulting in the average value of K₀ being higher than its stable value at 1600 kPa. For a given particle size and identical vertical stress level, higher initial relative density correlates with reduced lateral effective stress during consolidation. Moreover, the influence of relative density on test outcomes becomes increasingly pronounced with escalating vertical loading. A predictive formula for K₀ incorporating particle breakage is established. This formula can be used to quantify the effects of particle breakage on the coefficient of earth pressure at rest for coral sand. Particle breakage is identified as the primary driver of K₀ reduction in coral sand. The proposed formula provides a theoretical foundation for earth pressure calculations in island and reef engineering projects.