Fabric evolution and dilatancy within anisotropic critical state theory guided and validated by DEM

Abstract

Fabric, expressed by means of an evolving deviatoric fabric tensor F, plays a very important role in the anisotropic mechanical response of granular materials. The Anisotropic Critical State Theory (ACST) addresses fabric anisotropy by rendering dilatancy a function of F, in addition to other state variables. In this paper, 3D DEM is used to guide the specific grain-level definition of F, the formulation of its continuum evolution equation and its effect on anisotropic dilatancy within ACST. DEM provides stress-ratio and shear strain variations as input for ACST analytical calculations of evolving fabric tensor and dilatancy, which are then favourably compared with totally independent direct measurements of these quantities by DEM. Dilatancy is shown to be strongly affected by the contact normal-based fabric tensor Fc, whose evolution is best described by a continuum equation within ACST that includes dilatancy and a quantity related to particle orientation-based fabric tensor Fp. The aforementioned favourable comparison of the results for fabric tensor and dilatancy obtained independently by ACST and DEM, confirms the validity of the core framework of ACST irrespective of any constitutive model that addresses the deviatoric stress-strain relations.