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Experiments on the production of transverse grain alignment in a sheared dispersion |
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| Authors: | A I REES |
| Institution: | Institute of Oceanographic Sciences, Wormley, Godalming, Surrey GU8 5UB, U.K. |
| Abstract: | ABSTRACT A series of experiments was designed to investigate grain orientation in flows with concentrations of granular solids in the range from 0.5 to 15%. Fourteen experiments were carried out in which sand-sized material was dispersed in liquid plaster of paris and the dispersion allowed to flow down a slope until it came to rest. The preferred orientation of the grains was then estimated by measuring the anisotropy of magnetic susceptibility of specimens cut from the solidified flows. Five of the experiments showed signs of deformation, both in the gross characteristics of the flow and in the grain alignment. The remaining nine had grain alignment dependent on grain concentration. At concentrations of 1.2% and less and 11.1% and more, by volume, alignment of long axes was parallel to flow. These observations were consistent with the existing theories for low concentrations, in which preferred alignment is shown to result from the varying rate of rotation of grains in a shearing flow, and for high concentrations, in which preferred alignment results from the transfer of angular momentum between colliding grains. At some intermediate concentrations transverse alignment was observed. A theoretical explanation combining the theories of the extreme cases is suggested. The observation of transverse alignment is compared with a similar observation in some turbidites. |
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