Limiting mechanisms of slow dilatant plastic shear deformation of granular media

Abstract

The tendency in granular media to change volume during shear, known as dilatancy, was discussed first in 1886¹ and subsequently by other workers^2–5. Strength and resistance to slow deformation can be profoundly affected by dilatancy and this is important for the bulk handling of materials in the process industries and soil behaviour in civil engineering. Here we propose a minimal form of local collapse as a mechanism of slow steady-state deformation, complementing the familiar mechanism of potentially expansive sliding and rolling. Both are applied to ideal frictionless grains and involve, respectively, maximum and minimum rates of internal energy dissipation. Subsequent comparison to the behaviour of real granular material shows surprising similarities. Apparently, our proposed very simple idealization identifies the mechanisms in real materials and provides the possibility of quantitative predictions.