Citation

Gravish N, Goldman DI. Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 2014; 90(3): 032202.

Affiliation

School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.

Copyright

(Copyright © 2014, American Physical Society, Publisher American Institute of Physics)

DOI

unavailable

PMID

25314432

Abstract

We study the evolution and failure of a granular slope as a function of prepared volume fraction, ϕ_{0}. We rotated an initially horizontal layer of granular material (0.3-mm-diam glass spheres) to a 45^{∘} angle while we monitor the motion of grains from the side and top with high-speed video cameras. The dynamics of grain motion during the tilt process depended sensitively on ϕ_{0}∈[0.58-0.63] and differed above or below the granular critical state, ϕ_{c}, defined as the onset of dilation as a function of increasing volume fraction. For ϕ_{0}-ϕ_{c}<0, slopes experienced short, rapid, precursor compaction events prior to the onset of a sustained avalanche. Precursor compaction events began at an initial angle θ_{0}=7.7±1.4^{∘} and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle θ_{m}=28.5±1.0^{∘}. Granular material at ϕ_{0}-ϕ_{c}>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at θ_{0}=32.1±1.5^{∘} prior to the onset of an avalanche at θ_{m}=35.9±0.7^{∘}. Both θ_{0} and θ_{m} increased with ϕ_{0} and approached the same value in the limit of random close packing. The angle at which avalanching grains came to rest, θ_{R}=22±2^{∘}, was independent of ϕ_{0}. From side-view high-speed video, we measured the velocity field of intermittent and avalanching flow. We found that flow direction, depth, and duration were affected by ϕ_{0}, with ϕ_{0}-ϕ_{c}<0 precursor flow extending deeper into the granular bed and occurring more rapidly than precursor flow at ϕ_{0}-ϕ_{c}>0. Our study elucidates how initial conditions-including volume fraction-are important determinants of granular slope stability and the onset of avalanches.

Language: en