Influence of the Poisson effect on the stress dependence of the elastic moduli of soil

Effective medium theory and discrete-element method (DEM) simulations of smooth spheres both fail to correctly capture the small-strain stiffness of soil. The inability of the latter to capture small-strain stiffness can be overcome by adopting a rough-surface contact model which includes the effect of asperity deformation. Hertzian spheres are commonly used in DEM which neglect the Poisson effect, i.e., the lateral extension of a sphere orthogonal to an applied load. The hypothesis investigated in this paper is that this omission contributes to the inability of smooth-sphere DEM simulations to correctly capture the stress dependence of the elastic moduli of soil. This hypothesis was investigated using the finite-element method. At low to moderate confining stresses, the Poisson effect has little influence on the response. The Poisson effect becomes significant only at confining stresses on the order of 100 MPa, using parameters appropriate for a silica sand: stresses at which massive particle crushing would be expected. At lower stresses, rough-surface contact models remain the most justifiable way to match the stress–stiffness response measured in laboratory testing using DEM simulations.