Near-surface soils: discrete element modeling of self-supported unconfined drained sand specimens

Abstract

Recent findings demonstrate that traditional equations governing near surface, low confinement, soil mechanics may not accurately represent changes in soil strength, behavior, and structure, particularly for dry materials. These studies suggest that these inaccuracies may be due to the over-reliance of elastic principles in their respective formulations, and have found that as confinement decreases, the soil tends to resist continuum-type behavior. In practical modeling terms, these limitations would severely impact the use of traditional finite discretization methods that typically rely on continuum-based assumptions and often employ elastic constitutive laws. In this work the discrete element method is examined for its applicability in this regard. Specifically, a series of dry, unconfined, axial tests are numerically simulated and the applied axial force is compared with physical experiments. Various contributing factors, such as the use of spherical versus non-spherical particles, the degree of translational and rotational resistance, degree and method of compaction, and force chains, are considered. It was found that particularly important are the initial calibration tests for which unconstrained (free-standing) granular columns are feasible, including the parameter calibrations for the coefficient of sliding friction and angular rotation.