Analysis of the densification of a vibrated sand packing

Abstract

International audienceTwo techniques have been used to analyze the densification of silica sand by horizontal sinusoidal vibrations of frequency f = 50 Hz for relative accelerations between 0 and 6: the quantitative analysis of motion observed through the transparent wall, and the altitude map of the free top surface of the sample. The first technique was used to analyze the transient regime: during the first 10 s, slight densification occurs at the bottom of the powder bed, while the upper part enters convective motion and the intermediate part reaches densities higher than 66%. The second technique allowed to quantify the evolution of the overall density vs. acceleration Γ during the steady regime (dynamic density) and after the vibrations (relaxed density): a maximum density is observed in both cases for an optimal acceleration which depends on the initial height of the powder bed. These results are analyzed and discussed

Preface: Focus on imaging methods in granular physics

“…24 Another option is to restrict the data collection to the surface of the granular system, with the disadvantage that bulk properties can differ significantly from the behavior at the surface. [25][26][27][28][29][30] If the volume fraction of the particles is sufficiently low, stereo-camera or volumetric methods can be used to capture three-dimensional (3D) dynamics. [31][32][33] If the particles are optically transparent, there exist two additional options.…”

Ultrasonic compaction of granular geological materials

“…Although it has been reported that particle mineralogy and shape both affect the performance of an ultrasonic compaction 3 process [12,13], the influence of geological materials is unclear. There has been conflicting evidence between different studies with respect to the influence of vibrations on densification [14], and it has been proposed that significant differences between the physical properties of the particles, such as grain size and density, are contributory factors. It has also been reported that there is a significantly increased density and particle distribution uniformity within the granular material achieved when ultrasonic excitation is superimposed on the compaction process [9].…”

“…In the vibration of granular material such as sand particles, it is known that there is a stage at which the particles begin to behave more like a fluid than a solid. This can be referred to as the fluidisation transition [14]. Convection motion has been shown to be influential in how the particles move from a solid-like state to fluid.…”

“…A sample of material undergoing compaction could exist as solid, denselypacked material in one region, but fluidised in another. It has been reported that the physical properties of granular materials, such as the particle size and the density, can affect the densification [14], however it remains evident that three zones exist, comprising a lowermost marginally compacted area, a significantly compacted middle layer, and a fluidised top layer resulting from convection. The depth of the fluidised region has been reported to be only weakly linked to the initial sample density [14].…”

“…The influence of the direction in which the vibrations are applied to the substrate has also been reported [9,14,19]. In one study, a test setup was manufactured to generate vibrations in the plane of the face of a cylindrical sample (horizontal) and in the axial (vertical) direction [9].…”