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Packing-Induced Radial Particle-Size Segregation: Influence on Hydrodynamic Dispersion and Water Trausfer Measurements¹

ABSTRACT

Previous laboratory studies have shown that radial particlesize segregation occurs when soil columns are prepared with the aid of vibratory compaction. This segregation is characterized by a greater proportion of coarser particles near the periphery than in the central region of the column. A specially devised, alternative repacking technique, utilizing a vibration-free impacting apparatus, reduced such segregation in soil columns to an acceptably low level. Soil columns prepared by the above two packing procedures (i.e., with or without induced radial segregation) exhibited significant differences in their water flow and salt transport properties. Miscible displacement tests exhibited effluent-concentration histories that agree with currently accepted one-dimensional dispersion theory in the case of nonsegregated soil columns. On the other hand the results from segregated soil columns could not be reconciled with this theory. Horizontal infiltration into either segregated or nonsegregated soil columns produced significantly different moisture content profiles. However, it yielded rather similar relations between infiltration volume and the square root of time.

¹ Contribution from US Geological Survey, Menlo Park, Calif. 94025. Presented before Western Society of Soil Science, Univ. of Utah, Salt Lake City, Utah, June 14, 1973. Publication authorized by the Director, US Geological Survey.

² Research Soil Physicist, Research Chemist, and Research Soil Physicist, respectively.

Received for publication August 31, 1973. Accepted for publication October 2, 1973.