Particle Shape Effects on Packing Density, Stiffness, and Strength: Natural and Crushed Sands

TLDR

Particle size and shape reflect formation history, and macroscale soil behavior arises from particle‑level interactions influenced by shape characteristics such as sphericity, roundness, and smoothness. The study compiles experimental and published data into two databases to systematically assess how particle shape influences packing density and the mechanical properties of sandy soils, aiming to improve understanding of sand behavior. The authors assembled two databases of experimental and published data to investigate particle shape effects on packing density and mechanical properties across strain ranges. The data confirm that greater angularity or eccentricity increases maximum and minimum void ratios, while increased irregularity reduces stiffness, raises compressibility under zero‑lateral strain, and elevates the critical state friction angle and intercept, establishing particle shape as a key soil index property.

Abstract

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 ϕcs; 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.