Directional-dependence in the mechanical characteristics of sand: a review

The majority of granular soil is anisotropic material and it exhibits stress-strain variations depending on principal stress directions. Such directions acting on granular deposits vary with in situ loading conditions. Many experimental, numerical and analytical studies on anisotropy effects, as represented by principal stress rotation, on sand behaviour have been reported in the literatures, however, no attempt has been made to present an overview of this issue. Therefore, this review presents a comprehensive overview of the effect of anisotropy on sand behaviour, including the fabric effect, different fixed direction of principal stress and continuous rotation of the principal stress effects on the stress-strain response of sand in addition to bearing capacity under an inclination bedding plane. This review indicates that sand strength is affected strongly by the direction of principal stress, and strength decreases as the inclination increases, reaching a minimum value in the range of alpha = 60-90 degrees, although some studies report some increase in strength at alpha = 90 degrees. Moreover, the rotation of principal stress results in progress deformation with most of it occurring during the first cycles. Consequently, it is highly recommended to take anisotropy into consideration for any proper design of geotechnical problems. Ignoring anisotropy may lead to failure due to the overestimation of strength.