Strength and dilatancy of sands from their image-based intrinsic properties

Recent advances in image-based particle shape characterization allow reliably and rapidly determining particle roundness and sphericity of a statistically significant large number of particles, which enables systematic investigation of the influence of roundness and sphericity on macroscopic engineering behaviors such as strength and dilatancy of sands. This study collects 22 sands with a wide range of particle sphericity, roundness, gradations, and mean particle sizes. A total of 207 direct shear tests are prepared at various relative densities and normal stresses to establish the database. This database is further augmented by experimental data of another 97 sands from published geotechnical engineering sources. Influences of image-based sphericity, roundness, and gradation on the frictional and dilational components of soil strength are analyzed, leading to observations that angular, elongated, and well-graded sands exhibit larger values of critical strength, dilatancy, and peak strength. A material parameter is proposed by integrating roundness and gradation that captures the joint effects of intrinsic properties. The material parameter is used to develop predictive models for critical friction angles, dilation angles, and peak friction angles. The effectiveness and accuracy of the predicted models are validated by various published geotechnical experimental data. The material parameter and predictive models provide insights into relationships between micro particle level properties and macro mechanical behavior of sands and enable researchers and practitioners to rapidly estimate the strength and dilatancy of sands without performing laboratory tests.

Graphical Abstract