Nonlinear anisotropic modeling of dilative granular material behavior

A new cross-anisotropic model is proposed to predict the nonlinear dilative granular material behavior. A cross-anisotropic representation has different material properties (i.e., elastic modulus and Poisson's ratio) assigned in the horizontal and vertical directions. Repeated load triaxial test results with vertical and lateral deformation measurements performed on a variety of aggregate types were used to characterize the nonlinear stress dependent granular material behavior for horizontal, vertical, and the shear stiffnesses. Anisotropic elastic properties employed in the models satisfied thermodynamic considerations. The ratio of vertical to horizontal moduli, expressed as a measure of stiffness anisotropy, was generally larger than 1 with ratios rapidly increasing at higher principal stress ratios (sigma(1)/sigma(3)). Dilation was observed and accurately modeled using the anisotropic approach. Depending on the material type, varying degrees of dilation - as defined by the principal strain ratios (epsilon(1)/epsilon(3)) - were predicted at high principal stress ratios.