Measurement of surface deformation and cohesion of a granular pile under the effect of centrifugal force

TL;DR

This study develops an experimental setup to measure how granular piles deform under centrifugal force, revealing how cohesion influences deformation and slope development, with results validated against theoretical models.

Contribution

A novel apparatus for systematic measurement of granular pile deformation under centrifugal force, enabling analysis of cohesion effects on surface deformation and slope formation.

Findings

Granular piles deform significantly under centrifugal force.

Cohesive and non-cohesive piles show different deformation behaviors.

Deformation data align with theoretical parabola models.

Abstract

An experimental apparatus measuring free-surface deformation of a centrifuged granular pile is developed. By horizontally rotating a quasi two-dimensional granular pile whose apex is located at the vertical rotation axis, the resultant force of gravity and centrifuge yields the deformation of the granular pile. In this setup, centrifugal force depends on distance from the rotation axis whilst gravitational force is constant everywhere. Therefore, free-surface deformation by various centrifuge degrees can be systematically examined using this apparatus. In the system, a small unit consisting of a camera and computer is rotated with the granular sample to record the rotation-induced deformation. To evaluate the validity of the system, deformation of a rotated water surface is first measured and analyzed. The obtained data are properly explained by the theoretical parabolas without any fitting parameter. Next, we measure the deformation of non-cohesive and cohesive granular piles using the developed apparatus. Both granular samples show the significant deformation of granular pile and finally develop steep granular slopes on the side walls. However, details of the deformation processes depend on the cohesion strength. To quantitatively characterize the difference, the effective strength by cohesion and granular local-slope variations are analyzed based on the experimental results.