Investigation of the effect of particle size and strain level on the dynamic behaviour of carbonate sand

This study describes an experimental investigation of dynamic behaviours of carbonate sands containing two size groups (i.e., d = 2–3.2 mm and 3.2–4 mm) using resonant column (RC) and cyclic simple shear (CSS) tests over a wide shear strain range from γ = 1 × 10−4% to γ = 5%. Results show that shear modulus increases with confining pressure, while damping ratio decreases. At small strains, shear modulus increases with decreasing void ratios, but its influence becomes negligible at higher densities. More importantly, the shear modulus degradation curves exhibit a linear variation at γ < 10−3% and progressively a nonlinear variation given γ > 10−3%. Furthermore, the shear modulus of specimens of the size group d = 2–3.2 mm is consistently higher than that for specimens of d = 3.2–4 mm at both small and large shear strains, whereas a coupling effect from the particle size and strain level has been identified for the damping ratio, which is independent of particle size in case the shear strain is greater than 0.01%. A unified framework integrating RC and CSS results is proposed to characterise carbonate sand behaviour from small to large strains.