Effect of grain size distribution on the shear band thickness evolution in sand

Triaxial experiments were conducted on granular materials presenting uniform, graded and fractal particle distributions in order to investigate how the broadness of the distribution affects the phenomenon of strain localisation. The shear band thickness evolution is assessed by digital image correlation (DIC) using three cameras placed at different angles around a transparent triaxial cell. From the field of deformation, Gaussian distributions have made it possible to fit the data satisfactorily and determine the shear band width evolution. The latter exhibits a rapid decrease in the softening regime until a residual value is reached in all cases. In the conditions of the experiments, it is shown that the residual shear band thickness scales with the mean grain size and the ratio between the two increases with the broadness of the distribution. Samples with uniform distribution exhibit an average residual thickness of ∼ 10D₅₀, samples with graded distribution exhibit an average residual thickness of ∼ 12·5D₅₀ and samples with fractal distribution exhibit an average residual thickness of ∼ 17D₅₀.