Force chain collapse as grain column buckling in granular materials

Granular materials react under external loading by self-organizing the topology of the grain assembly. Thus, quasi-linear grain patterns, known as force chains, develop within the assembly to carry the main part of the external loading. The stability of these grain patterns controls the strength of the material, under given loading conditions. This manuscript investigates the mechanical behavior of such grain columns and exhibits some instability modes that can occur even when the local behavior at the contact between grains is purely elastic. First, an analytical approach is developed, and the ability of a grain column to collapse is demonstrated. Then this result is confirmed from numerical simulations performed using a discrete element method.