On the origins of reverse Janssen effect

TL;DR

This paper investigates the reverse Janssen effect, where the force on a granular column's base exceeds its weight, revealing that pouring protocol significantly influences this counterintuitive phenomenon through experiments and simulations.

Contribution

It demonstrates how pouring height and flux affect the reverse Janssen effect, providing new insights into granular force distributions and protocol dependence.

Findings

Reverse Janssen effect can be an order of magnitude stronger with higher pouring heights.

Pouring protocol significantly influences the magnitude of the reverse Janssen effect.

Experimental and computational results show strong protocol dependence of granular force distribution.

Abstract

We consider experimentally and computationally the phenomenon of the reverse Janssen effect, involving the counterintuitive finding that the force on the base of a column containing granular particles may be larger than the weight of the granular material itself. This finding is in contrast to the common Janssen effect, for which the force on the base is smaller than the particle weight, illustrating one of the best-known differences between granular and liquid systems. We find that the reverse Janssen effect is strongly influenced by the pouring protocol: under Earth's gravitational field, we find that the reverse Janssen effect is strongly and consistently influenced by the pouring height, as well as by (to somewhat lesser degree) pouring flux. Pouring grains from the height measured in tens of particle diameters leads to a reverse Janssen effect that is an order of magnitude stronger than the one found for small pouring heights of few particle diameters. This influence of the particles' delivery protocol allows for the development of a better understanding of the general features of the reverse Janssen effect and of the comparison between experiments and simulations reported in this and previous works.