Two-dimensional and three-dimensional inherent fabric in cross-anisotropic granular soils

This paper characterizes fabric anisotropy of granular soils by using both two-dimensional (2D) and three-dimensional (3D) images and evaluates the accuracy and effectiveness of using 2D images to characterize fabric anisotropy in 3D soils. The X-ray computed tomography (X-ray CT) is used to reconstruct the 3D volumetric images of five air-pluviated sand specimens. Then, six slices are obtained by vertically cutting the 3D volumetric image in an angle increment of 30 degrees. The 3D and 2D images are analyzed to determine long axis fabric, contact normal fabric, and branch vector fabric. The results show that 2D images produce satisfactory predictions for long axis fabric and branch vector fabric. The 2D images produce satisfactory predictions for contact normal fabric for rounded to well-rounded sands, but underestimate or contain large uncertainties to predict contact normal fabric for very angular to sub-rounded soils. This study shows that particle shapes affect the inherent fabric anisotropy in sands. Elongated sands tend to have stronger degrees of long axis and branch vector fabric anisotropy. Angular sands tend to have stronger degrees of contact normal fabric anisotropy.