عنوان مقاله [English]
In this study the effect of initial principal stress rotation on anisotropic behavior of medium dense Firoozkuh sand in drained condition was studied. Hollow Cylindrical Apparatus (HCA) was used to conduct the tests in drained condition on the medium dense specimens of Firoozkuh sand. All specimens were prepared with a height of 200 mm and outer and inner diameters of 100 and 60 mm, respectively using dry air pluviation method. The specimens were consolidated subjected to the anisotropic initial stresses with different directions (c). During consolidation, stress ratio (Rc = ’1c/’3c) was maintained to be equal to 2. Specimens were consolidated under an anisotropic condition in which the rotation of initial principal stresses had been set to a constant value varying from zero to 45o. The specimens are sheared under different inclinations of principal stress increments () varying from zero to 45 o. In these tests, the direction of principal stress increments () may be not equal to the direction of the principal stress due to anisotropic stresses, applied in consolidation phase. Generally, the results showed a decrease in the shear strength of sand by increasing . The results showed that the stress-strain behavior and shear strength of medium dense sand is influenced by the inclination of initial principal stresses. Initial anisotropic principal stresses cause initial shear strains which soften the stress-strain behavior of sand. Therefore the shear modulus and shear strength for anisotropic consolidated specimens was less than that of the isotropic consolidated specimens. The anisotropic response of medium dense sands is observed to be governed by c. It was found that the shear modulus and shear strength of sand relatively decreased and anisotropy coefficient significantly increased when anisotropic initial stress and increments of principal stresses are in the same direction. The effect of initial stress state on the shear modulus was more noticeable than that on the shear strength of sand.