Experimental investigation of shear strength of sands with inherent fabric anisotropy

Loading direction-dependent strength of sand has been traditionally characterized in the principal stress space as a direct extension of the Mohr-Coulomb criterion. A recent study found that it is more appropriate to define anisotropic strength of sand on failure/shear planes, but this proposition has only been demonstrated with discrete element method (DEM) simulations. The present study experimentally investigates anisotropic shear strength of sands in this new framework. Three granular materials with distinct grain characteristics ranging from smooth and rounded particles to flaky and angular particles are tested with the bedding plane inclination angle psi (b) varying over the full range of 0A degrees-180A degrees. The main objective is to study how the peak friction angle I center dot (p) of sand is affected by the psi (b) angle and how the psi (b)-I center dot (p) relationship evolves with the change of characteristics of constituent sand particles. We find that the general trend of psi (b)-I center dot (p) curves for real sands resembles what was predicted by DEM in a previous study, whereas rich anisotropic strength behavior is revealed by the laboratory data. The effects of normal stress and initial density, as well as shear dilation behavior at different shear directions, are also studied.