Effect of initial grading on shear behavior and particle crushing of dry calcareous sands

This study investigates crushable calcareous sand behavior under varying initial gradations and normal pressures using direct shear tests combined with high-performance acoustic emission (AE) measurements. Results reveal that increasing initial grading size, featured with specific particle morphologies, causes an initial reduction followed by a rise in shear strength and modulus, with shear stress-displacement curves transitioning from strain-softening to strain-hardening behavior. AE activity closely correlates with macroscopic mechanical responses: both larger initial particle sizes and higher normal stresses generate more AE hits. A strong linear relationship ( R 2 = 0 . 90 ) on a double-logarithmic scale between high-frequency AE hits and the breakage index confirms that high-frequency AEs serve as an effective indicator of particle crushing. The evolution of AE hit rate and dominant frequency response also vary markedly with initial gradation. Finer gradations exhibit three-stage AE evolution (rapid increase, decrease, and stabilization), dominated by low-frequency (