Effects of particle sphericity on shear behaviors of uniformly graded sand: Experimental study based on 3D printing

Abstract

This paper presents an experimental study on how particle sphericity affects the shear behaviors of uniformly graded sand. Using the Wadell 3D sphericity index S, the study examines natural calcareous sand and quartz sand grains. Five typical forms with varying sphericities were selected: S0 represents a perfect sphere (S = 1.000), while S1, S2, S3, and S4 denote irregular forms derived from natural calcareous sand and quartz sand, with S values of 0.954, 0.914, 0.888, and 0.848, respectively. Artificial sand particles with specific sphericities were then fabricated using a 3D printer. A series of consolidated-drained triaxial compression tests were conducted on these artificial sand particles at four different confining pressures ranging from 20 kPa to 100 kPa. The results show that the shear strength of sand increases with decreasing sphericity, as evidenced by an increase in both peak-state and critical-state friction angles. This suggests that irregular shapes enhance the shear strength of sand. Regarding the sand dilatancy under shear, the relationship with sphericity is complicated. As sphericity decreases, the maximum dilation angle increases under a low confining pressure, whereas it initially decreases and then increases under high confining pressures. Predictive models, which are capable of estimating peak-state friction angle, critical-state friction angle, and maximum dilation angle, were developed for a given sphericity and confining pressure. Verification of Bolton’s stress-dilatancy equation revealed a constant dilatancy coefficient for the artificial sand particles with different sphericities, suggesting that the contribution of dilatancy to the excess strength of sand remains independent of particle shape.