Reverse Janssen effect in narrow granular columns

TL;DR

This paper reports a novel reverse Janssen effect in narrow granular columns where the bottom supports more than the total weight, challenging previous assumptions about stress distribution in granular materials.

Contribution

It introduces the first experimental and numerical demonstration of the reverse Janssen effect and proposes a model explaining the stress-dependent constitutive relations.

Findings

Reverse Janssen effect observed in narrow columns

The bottom supports more than the total weight of grains

A model reproduces the stress-dependent behavior

Abstract

When grains are added to a cylinder, the weight at the bottom is smaller than the total weight of the column, which is partially supported by the lateral walls through wall/grain frictional forces. This is known as the Janssen effect. Via a combined experimental and numerical investigation, here we demonstrate a reverse Jansen effect whereby the fraction of the weight supported by the base overcomes one. We characterize the dependence of this phenomenon on the various control parameters involved, rationalize the physical process responsible for the emergence of the compressional frictional forces responsible for the anomaly, and introduce a model to reproduce our findings. Contrary to prior assumptions, our results demonstrate that the constitutive relation on a material element can depend on the applied stress.