Sensitivity to solid volume fraction of gravitational instability in a granular medium

Bonnet, Félix; Richard, T.; Philippe, Pierre

doi:10.1007/s10035-010-0178-7

Cited by 11 publications

(12 citation statements)

References 34 publications

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“…As in a previous experiment [15] we identified the volume fraction corresponding to the onset of dilation under shear, φ c , and showed that the dynamics of force and flow qualitatively differ across this transition. Similar observations of varying failure modes as a function of initial φ have been made in avalanche [37,38] experiments, and indicate that granular failure is sensitive to volume fraction across a range of perturbation methods. Our experiments highlight a number of nontrivial phenomena associated with granular drag and its dependence on φ.…”

Section: Discussionsupporting

confidence: 71%

Force and flow at the onset of drag in plowed granular media

2014

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We study the transient drag force FD on a localized intruder in a granular medium composed of spherical glass particles. A flat plate is translated horizontally from rest through the granular medium to observe how FD varies as a function of the medium's initial volume fraction, ϕ. The force response of the granular material differs above and below the granular critical state, ϕc, the volume fraction which corresponds to the onset of grain dilatancy. For ϕ<ϕc FD increases monotonically with displacement and is independent of drag velocity for the range of velocities examined (<10 cm/s). For ϕ>ϕc, FD rapidly rises to a maximum and then decreases over further displacement. The maximum force for ϕ>ϕc increases with increasing drag velocity. In quasi-two-dimensional drag experiments, we use granular particle image velocimetry (PIV) to measure time resolved strain fields associated with the horizontal motion of a plate started from rest. PIV experiments show that the maxima in FD for ϕ>ϕc are associated with maxima in the spatially averaged shear strain field. For ϕ>ϕc the shear strain occurs in a narrow region in front of the plate, a shear band. For ϕ<ϕc the shear strain is not localized, the shear band fluctuates in space and time, and the average shear increases monotonically with displacement. Laser speckle measurements made at the granular surface ahead of the plate reveal that for ϕ<ϕc particles are in motion far from the intruder and shearing region. For ϕ>ϕc, surface particles move only during the formation of the shear band, coincident with the maxima in FD, after which the particles remain immobile until the sheared region reaches the measurement region.

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Section: Discussionsupporting

confidence: 71%

Force and flow at the onset of drag in plowed granular media

2014

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“…The effect of φ 0 on avalanche onset has been systematically studied in granular suspension experiments in which the granular material is immersed in a fluid. Results from these experiments [22,24,25] give an indication of what we may expect in dry granular materials: increasing φ 0 increases the angle of maximum stability. However, granular suspensions, with the presence of a viscous interstitial fluid, differ from dry granular materials.…”

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confidence: 77%

Effect of volume fraction on granular avalanche dynamics

Gravish

Goldman

2014

Phys. Rev. E

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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.

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“…Therefore, the shape and diameter of the crater rim must be affected by the packing fraction mainly in a later stage. This gives the impression that events occurring after the opening of the crater, such as splashing [19,25] and avalanches [26][27][28], shape the final crater rim diameter in a profound way. Furthermore, Fig.…”

Section: Crater Evolutionmentioning

confidence: 99%

Crater formation during raindrop impact on sand

2017

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After a raindrop impacts on a granular bed, a crater is formed as both drop and target deform. After an initial, transient, phase in which the maximum crater depth is reached, the crater broadens outwards until a final steady shape is attained. By varying the impact velocity of the drop and the packing density of the bed, we find that avalanches of grains are important in the second phase and hence, affect the final crater shape. In a previous paper, we introduced an estimate of the impact energy going solely into sand deformation and here we show that both the transient and final crater diameter collapse with this quantity for various packing densities. The aspect ratio of the transient crater is however altered by changes in the packing fraction.

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Sensitivity to solid volume fraction of gravitational instability in a granular medium

Cited by 11 publications

References 34 publications

Force and flow at the onset of drag in plowed granular media

Force and flow at the onset of drag in plowed granular media

Effect of volume fraction on granular avalanche dynamics

Crater formation during raindrop impact on sand

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