Particle shape effects on packing density, stiffness, and strength: Natural and crushed sands

The size and shape of soil particles reflect the formation history of the grains. In turn, the macroscale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness, and smoothness characterize different scales associated with particle shape. New experimental data and results from published studies are gathered into two databases to explore the effects of particle shape on packing density and on the small-to-large strain mechanical properties of sandy soils. In agreement with previous studies, these data confirm that increased angularity or eccentricity produces an increase in emax and emin. Furthermore, the data show that increasing particle irregularity causes a decrease in stiffness yet heightened sensitivity to the state of stress; an increase in compressibility under zero-lateral strain loading; an increase in the critical state friction angle Φ_cs; and an increase in the intercept Γ of the critical state line (there is a weak effect on the slope λ). Therefore, particle shape emerges as a significant soil index property that needs to be properly characterized and documented, particularly in clean sands and gravels. The systematic assessment of particle shape will lead to a better understanding of sand behavior.