<p>A series of drained triaxial shear tests were conducted to investigate the breakage evolution and energy dissipation mechanisms of saturated quartz sand under high-stress conditions. The test results show that the mechanical properties of saturated sand are significantly affected by the effective confining pressure. The content evolution of each quartz sand particle fraction is governed by the interplay between particle breakage and replenishment. Axial strain and confining pressure synergistically shift particle size distribution curves rightward, with the area between pre-/post-test particle size distribution curves expanding markedly as both parameters increase. Higher confining pressure amplifies the effect of axial strain on the relative breakage index. Energy dissipation comprises three components: shear dilation energy, particle friction energy, and particle breakage energy. Shear dilation energy constitutes a minor portion of total input energy, while both particle friction and particle breakage energy show positive correlations with confining pressure and axial strain. Finally, a hyperbolic function establishes the particle breakage energy-axial strain relationship through regression analysis.</p>