An improved direct shear apparatus for shear strength of anisotropic sands and its primary application

The deformation and shear strength of anisotropic granular materials are dependent on the shearing direction or the orientation of principal stress relative to the bedding plane. In order to investigate the shear strength properties of any shear plane for anisotropic granular materials, an improved direct shear apparatus was designed, with which the ω of Fujian standard sand defined as the angle of shear plane with respect to the bedding plane can be changed in the whole range of 0°-180°. The characteristics of the improved direct shear apparatus is that its walls are independent and demountable, thus the apparatus can be assembled according to different needs; and some top and side surfaces can be opened. By using the improved direct shear apparatus, direct shear tests are conducted on Fujian standard sands with the variation of ω from 0° to 180° at intervals of 15°. The experimental results show that the plane with the minimum peak internal friction angle is achieved at the angle of ω from 0° to 90°. After that, the peak internal friction angle increases with the increasing ω. However, the plane with maximum peak internal friction angle is not the plane perpendicular to the depositional plane(ω = 90°), but that with ω ≈105°. The planes related to the maximum and minimum peak internal friction angles are dependent on the anisotropy degree of materials.