Formulation of Anisotropic Strength Criteria for Cohesionless Granular Materials

Abstract

Granular materials deposited under gravity usually exhibit inherent fabric anisotropy, which leads to profoundly varying strength under different loading directions in regard to the bedding plane that has been observed through experiments and numerical simulations. Classical isotropic strength criteria that are only stress dependent cannot describe such anisotropy in strength. This study introduces an anisotropic strength variable Λ that measures the distance between the bedding plane and the maximum shear stress ratio plane, thus incorporating both the stress tensor and the material orientation, and guarantees objectivity. The strength variable Λ is adopted to construct a general formulation that allows for the extension of many existing isotropic strength criteria to become anisotropic. The formulation requires only the following two parameters: kf0, reflecting the minimum strength of the material, and a, reflecting the intensity of inherent anisotropy. The two parameters can be conveniently calibrated. The proposed strength criteria formulation is validated against both physical tests and discrete-element method (DEM) simulations on various granular materials, showing its capability in describing the anisotropic strength. The anisotropic strength criteria formulation is applied to analysis of passive earth pressure to showcase the significance that considerations for strength anisotropy could make to geotechnical design.