Experimental investigation on the inherent and initial induced anisotropy of sand

Abstract

In this paper, an experimental study concerning the relevance of the initial stress state and the inclination of principal effective stress to vertical (α) on the behavior of sand is presented. The study was carried out using the dry air pluviated Firoozkuh sand in a hollow cylinder apparatus. Most of the specimens were consolidated subjected to the anisotropic initial stress state, which is made by maintaining the principal stress ratio (i.e., Rc) and the inclination of initial principal stress (i.e., Rc) constant during the consolidation phase. Shear loading was carried out in the drained condition while the value of α and intermediate principal stress ratio (i.e., b) were held constant. Sands subjected to the anisotropic vertical initial stress (Rc = 2, αc = 0) are found to be highly influenced by α due to initial induced anisotropy in addition to inherent anisotropy. The anisotropic response of medium dense sands is observed to be strongly dependent on αc. The effect of soil anisotropy, specifically initial induced anisotropy, on the shear modulus is more noticeable than the shear strength. The initial induced anisotropy due to the initial stress state of medium dense sand may have a significant influence on the deformation of geotechnical structures such as shallow foundations, so that its neglecting may lead to unsafe designs.