Modified direct shear test for anisotropic strength of sand

This paper presents a simple method to estimate the directional dependency of granular soil strength using a modified shear box and a special specimen preparation procedure. This method is used to investigate the strength anisotropy of granular materials with particle shapes varying from spherical to angular. The experimental results show that the friction angle of granular materials varies with the orientation of shear plane relative to the bedding plane, and the degree of anisotropy is affected by particle shape. Comparison of the data from direct shear tests in this study with those of plane strain and torsional simple shear tests in the literature shows that direct shear using the modified direct shear box can reasonably capture the directional dependency of the friction angle for cohesionless materials.