Starting to move through a granular medium

TL;DR

This study investigates the force needed to start moving a flat plate through a granular medium, revealing a linear relationship with plate diameter and dependence on grain size, highlighting dilation effects.

Contribution

It introduces a measurement of initiation force that depends on grain size and plate diameter, contrasting with steady-state drag measurements.

Findings

Initiation force scales linearly with plate diameter.

Initiation force depends on grain size.

Dilation of grains around the plate is key to force requirements.

Abstract

We explore the process of initiating motion through a granular medium by measuring the force required to push a flat circular plate upward from underneath the medium. In contrast to previous measurements of the drag and penetration forces, which were conducted during steady state motion, the initiation force has a robust dependence on the diameter of the grains in the medium. We attribute this dependence to the requirement for local dilation of the grains around the circumference of the plate, as evidenced by an observed linear dependence of the initiation force on the plate diameter.