Document Type : Research Article
PhD Candidate, Civil Engineering Department, Urmia University, Urmia, Iran
Associate Professor, Civil Engineering Department, Urmia University, Urmia, Iran
The inherent anisotropic behavior of sands and the grain size effects are studied in this paper. A series of undrained torsional shear tests with constant inclination angle (α°) and intermediate principle stress ratio (b) were conducted by hollow cylindrical torsional apparatus (HCTA) on four types of sand. This study furthers the knowledge on the dependency of steady states on anisotropy sands with different shape and size properties. In doing so, the direction of principal stress orientation is varied from 15° to 60°, for an intermediate principle stress ratio of 0.5 and 1.0 and constant initial confining pressure. The results show that by increasing the particle sizes, the behavior of sands changes from contractive behavior to fully hardening and dilative behavior. Also, it observed that the effect of anisotropy in coarse grain sands is more than fine grain sands. In this study two-dimensional image analysis has been adapted to classify particle shape properties. These morphological characteristics were determined from the analysis of scanning electron microscope images and were defined as sphericity and roundness. The results of the experiments on all four types of sand show that the anisotropy effects decrease by increasing the sphericity, but in coarse grain sands roundness of grains have no much effect on the behavior and anisotropy.