# Dynamics of a grain-scale intruder in a two-dimensional granular medium with and without basal friction

## TL;DR

This study investigates how a grain-sized intruder moves through a 2D granular medium, revealing how basal friction influences the transition between intermittent flow and stick-slip regimes, with implications for understanding granular flow dynamics.

## Contribution

It provides experimental insights into the role of basal friction in intruder dynamics and identifies how frictional conditions affect flow regimes in granular materials.

## Key findings

- Basal friction causes a smooth crossover between flow regimes.
- Reducing interparticle friction shifts stick-slip to higher packing fractions.
- Eliminating basal friction results in persistent intermittent flow.

## Abstract

We report on a series of experiments in which a grain-sized intruder is pushed by a spring through a 2D granular material comprised of photoelastic disks in a Couette geometry. We study the intruder dynamics as a function of packing fraction for two types of supporting substrates: a frictional glass plate and a layer of water for which basal friction forces are negligible. We observe two dynamical regimes: intermittent flow, in which the intruder moves freely most of the time but occasionally gets stuck, and stick-slip dynamics, in which the intruder advances via a sequence of distinct, rapid events. When basal friction is present, we observe a smooth crossover between the two regimes as a function of packing fraction, and we find that reducing the interparticle friction coefficient causes the stick-slip regime to shift to higher packing fractions. When basal friction is eliminated, we observe intermittent flow at all accessible packing fractions. For all cases, we present results for the statistics of stick events, the intruder velocity, and the force exerted on the intruder by the grains. Our results indicate the qualitative importance of basal friction at high packing fractions and suggest a possible connection between intruder dynamics in a static material and clogging dynamics in granular flows.