Grain shape effect on the anisotropic behaviour of silt–sand mixtures

Abstract

The anisotropy of sand–silt mixtures has not been fully studied in terms of the effects of different grain shapes and silt content. This study investigated the effects on anisotropy in three different sands with various silt contents and grain shapes. The tests performed in this research include 90 hollow cylinder torsion shear tests conducted on three types of sand: Hamadan sand with high angularity, Firoozkuh sand with medium angularity and Tehran sand with low angularity. The samples had silt contents of 0, 15, 30 and 50 per cent. To define the shape criteria in this study, two ratios were defined. The first was roundness, which can be obtained from the ratio of the radius of the corners of the grains to the largest circle that encompasses the entire grain; this ratio is denoted by rr. The second criterion was sphericity, which can be obtained by dividing the smallest pictorial width by the minimum graphical length; this ratio is denoted by rs. Under similar initial effective confining pressures, sand with high roundness and sphericity showed contractive behaviours. An increase in silt content, as well as in the ratios rr and rs, decreased the sample strength. Moreover, increasing these two ratios caused the stress–strain curves to be close to one another.

Monotonic Behaviour of Sand Under Torsional Loading With Different Confine Stress

“…This behavior has been confirmed and described by Yoshimine and Ishihara [29] for Toyoura sand and by Khayat, et al [1] for a Firoozkuh sand-silt mixture.…”

“…Some researcher has extensively described the non-coaxial behavior of sand under various stress paths through a series of HCTS tests [1,16,19]. The non-coaxial behavior was found to depend on the type of sand, relative density of the sample and on the direction of stress increment, and was also found to decrease with increasing strains [20].…”

“…The stress-strain behavior of sands under monotonic loading has been the subject of various studies in the past [1][2][3]. Key parameters-such as density, grain size distribution, particle shape and mineralogy, a method of sample preparation, the direction of loading, and anisotropy that affect the behavior of a sand under monotonic loading have been presented widely [3][4][5][6].…”

“…One of the objectives was to recognize the yield surface within the light of the elastoplasticity framework. Therefore, in the following decades, with advances in measurements and control techniques, complex machines such as the true triaxial, by Arthur and Menzies [15]; hollow cylinder torsional shear (HCTS) by Hight, et al [16]; Khayat, et al [1]; and plane strain machines by Park, et al [17], were used to further explore the role of induced anisotropy, principal stress rotation and intermediate principal stress.…”

Editorial

“…The sixth paper, by Khayat et al (2014), considers the effect of grain shape on the anisotropic behaviour of silt-sand mixtures. The authors present the results of 90 hollow cylinder torsion shear tests conducted on three types of sand with different angularity but similar particle size distributions, mixed with different amounts of silt.…”