Abstract
We studied experimentally the effect of grain size and maximum load on the compaction and subsequent relaxation of a granular column when it is subjected to vertical uniaxial compression. The experiments were performed using two different types of grains: 1) solid glass beads, and 2) porous beads that consist of agglomerates of glass powder. We found that the compression force increases non-linearly with time, with sudden drops for the case of glass beads and periodic undulations for dust particles. Whereas the grain size effect is small in the average force load, the fluctuations become larger as the grain size increases. On the other hand, the relaxation process is well described by the Maxwell model with three different relaxation time scales.
Highlights
The relaxation process of a granular material after being continuously compressed is not totally well understood. This is reflected for instance in the undesirable sinking of airports and highways [1], where the relaxation times result considerably shorter than those estimated from existing models. This is in part because the relaxation dynamics strongly depends on the compression process and on the particles nature, as it has been revealed by di↵erent studies focused on the uniaxial vertical compression of granular materials and powders [2,3,4,5,6,7]
We extend our previous research [7] by exploring the e↵ect of the grain size on the compression and relaxation dynamics of a granular column composed of solid beads or hierarchical granular matter
For the case of hierarchical granular matter [7], we reported recently that the compression of granular columns composed of 1 mm dust aggregates was characterized by periodic undulations of the force load with wavelengths dependent on the compression rate, followed by a multi
Summary
The relaxation process of a granular material after being continuously compressed is not totally well understood This is reflected for instance in the undesirable sinking of airports and highways [1], where the relaxation times result considerably shorter than those estimated from existing models (e.g. the Maxwell model). The amplitudes of the sudden force drops for glass beads and undulations for dust particles increase notably with the grain size For both materials, the relaxation dynamics is well described by the Maxwell model using three exponential to slow oscillatory compaction decreases logarithmically; terms with short, medium and long characteristic times. For the case of hierarchical granular matter [7], we reported recently that the compression of granular columns composed of 1 mm dust aggregates was characterized by periodic undulations of the force load with wavelengths dependent on the compression rate, followed by a multi-
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