Granular packings with moving side walls

TL;DR

This study uses simulations to examine how moving side walls affect stress distribution and force networks in confined granular packings, revealing significant changes from static states and dependencies on wall velocity.

Contribution

It provides new insights into how wall movement influences stress profiles and force chains in granular materials, extending understanding beyond static packings.

Findings

Final stress states differ from initial static packings.

Wall movement alters stress profiles, fitting Janssen's model at high velocities.

Force networks increase at Coulomb criterion with wall movement.

Abstract

The effects of movement of the side walls of a confined granular packing are studied by discrete element, molecular dynamics simulations. The dynamical evolution of the stress is studied as a function of wall movement both in the direction of gravity as well as opposite to it. For all wall velocities explored, the stress in the final state of the system after wall movement is fundamentally different from the original state obtained by pouring particles into the container and letting them settle under the influence of gravity. The original packing possesses a hydrostatic-like region at the top of the container which crosses over to a depth-independent stress. As the walls are moved in the direction opposite to gravity, the saturation stress first reaches a minimum value independent of the wall velocity, then increases to a steady-state value dependent on the wall-velocity. After wall movement ceases and the packing reaches equilibrium, the stress profile fits the classic Janssen form for high wall velocities, while it has some deviations for low wall velocities. The wall movement greatly increases the number of particle-wall and particle-particle forces at the Coulomb criterion. Varying the wall velocity has only small effects on the particle structure of the final packing so long as the walls travel a similar distance.