Studies of local jamming via penetration of a granular medium

TL;DR

This study investigates how the bottom boundary of a container influences the force needed to penetrate a dense granular medium, revealing an intrinsic length scale related to local jamming unaffected by velocity or grain size.

Contribution

It identifies a boundary-dependent length scale for local jamming in granular media, advancing understanding of penetration mechanics in such systems.

Findings

Penetration force near the bottom boundary is significantly affected by surface properties.

An intrinsic length scale for jamming depends on plate size and stress, not velocity or grain size.

The length scale exhibits a square root dependence on plate radius and stress.

Abstract

We present a series of measurements examining the penetration force required to push a flat plate vertically through a dense granular medium, focusing in particular on the effects of the bottom boundary of the vessel containing the medium. Our data demonstrate that the penetration force near the bottom is strongly affected by the surface properties of the bottom boundary, even many grain diameters above the bottom. Furthermore, the data indicate an intrinsic length scale for the interaction of the penetrating plate with the vessel bottom via the medium. This length scale, which corresponds to the extent of local jamming induced by the penetrating plate, has a square root dependence both upon the plate radius and the ambient granular stress near the bottom boundary, but it is independent of penetration velocity and grain diameter.