Effect of Crushability on the Drained Shear Behavior of Carbonate Sand

• A total of 66 drained shear tests were conducted on carbonate with four initial PSDs to investigate the shear behavior and breakage evolution. • Higher crushability leads to faster reductions in peak strength, dilatancy, and strain softening as confining pressure increases. • Secant stiffness E 50 evolves in three distinct trends based on crushability. • More crushable sands exhibit a faster decrease in peak strength with increasing breakage index B g . Soil crushability reflects the susceptibility of granular materials to particle breakage and significantly affects their shear response. A grading index proposed by Muir Wood and co-workers was adopted to quantify crushability arising from different initial gradations. Carbonate sand specimens were prepared with four initial gradations: uniform, gap, fractal A, and fractal B, covering a range of crushability. A total of 66 drained shear tests were conducted over three relative densities and a wide range of confining pressures to investigate the shear behavior and breakage evolution of carbonate sand. The results show that with increasing confining pressure, the degree of strain softening, dilatancy, and peak strength all decrease at rates that depend on soil crushability. This decrease tends to stabilize as soil crushability decreases. The relation between secant modulus E 50 and confining pressure also varies with crushability. For confining pressures beyond about 200 kPa, E 50 decreases in the most crushable specimens (uniform gradation), remains approximately unchanged in the intermediate-crushability sands (gap and fractal A gradations), and continues to increase in the least crushable sands (fractal B gradation). By correlating peak strength with the degree of particle breakage, differences in crushability were found to be closely associated with the shear responses of carbonate sand. These findings provide a useful reference for the safe design of island and reef infrastructure foundations in the South China Sea.