Influence of Particle Morphology on the Friction and Dilatancy of Sand

The shear strength of granular materials is influenced by many factors that include particle morphology, gradation, mineralogy, fabric, material density, applied stresses, boundary conditions, and loading path. In recent years, three-dimensional (3D) imaging techniques such as computed tomography enabled researchers to quantify sand particle morphology based on 3D images of particles. This paper presents an experimental investigation of the influence of particle morphology (i.e., surface texture, roundness, form, and sphericity), specimen density, and initial mean stress on the shear strength properties of dry specimens of silica sands and glass beads. Spherical glass beads as well as three other sands (with different morphologies) with grain sizes between U.S. Sieve No. 40 (0.42 mm) and Sieve No. 50 (0.297 mm) were tested at 15-, 50-, 100-, and 400-kPa confining pressures under axisymmetric triaxial compression. The influence of particle morphology on stress-strain response and volume change behavior as well as peak state and critical state (CS) friction and dilatancy angles was examined. The triaxial test results of Toyoura and Hostun RF sands collected from the literature were included in the analyses. Simple statistical models capable of predicting the peak and CS friction angles as well as dilatancy angle by providing particle surface texture, roundness, sphericity, relative density, and initial mean stress as input parameters were developed. The results show that morphology parameters highly influence dilatancy angle, CS, and peak state friction angles. (C) 2017 American Society of Civil Engineers.