A Dilatancy Based Anisotropic Model for Granular Material

Soil is generally a heterogeneous material and most natural soil deposits show a some stratification. The mechanical behavior of such material differs in different directions, especially in the direction parallel and perpendicular to the stratification. A series of isotropic compression tests were carried out to study the behavior of granular material produced under controlled stratification in the laboratory. These tests were conducted both on cylindrical and square prismatic triaxial specimens. It was observed that for hydrostatic loading the strain response was different in different directions, especially in directions parallel and perpendicular to the direction of soil deposition. A definite trend of anisotropy was observed in the deformation pattern. This paper focuses on predicting the anisotropic strain response of stratified soil deposits subjected to isotropic compression. Anisotropy is modeled in this paper by treating soil-dilatancy as a variable quantity. The proposed anisotropic model is incorporated within an existing strain-hardening model. It has a modified plastic potential function with an associated and identical cap yield surface function to account for the anisotropic response observed in isotropic compression tests. The cap yield surface is supplemented by a shear hardening Mohr–Coulomb surface in the deviator direction.