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Published in Soil Sci Soc Am J 23:422-428 (1959)
© 1959 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Equilibrium of Soil Grains at the Threshold of Movement by Wind1

W. S. Chepil2

ABSTRACT

This paper, based on wind tunnel studies, presents an analysis of the nature and magnitude of forces on soil grains at the threshold of their movement by wind. Forces of drag, lift, and gravity were analyzed in relation to each other.

The equilibrium between these forces and the soil grains was found to be influenced by the diameter, shape, and immersed density of the grains, the angle of repose ø' of the grains with respect to the mean drag level of the fluid, the closeness of packing {eta} of top grains on the sediment bed, and the impulses of fluid turbulence TD and TL associated with drag and lift, respectively. All those factors were measured and related with actual and theoretical forces involved.

New approaches to measurement of {eta}, ø', TD and TL are presented. Analyses indicate that the magnitude of pressure impulses of both TD and TL is statistically distributed according to the somewhat skewed normal error law. The ratio of mean pressure to standard deviation {sigma} was constant for any size of grains or fluid velocity and could be expressed by equation {sigma} = cP in which P is the mean pressure of lift or drag and c is a constant which was found to have a mean value of 0.49.

NOTES

1 Contribution from Soil and Water Conservation Research Division, ARS, USDA, Kansas Agr. Exp. Sta. cooperating. Department of Agronomy contribution No. 621. Presented before Div. I, Soil Science Society of America, Aug. 7, 1958, at Lafayette, Ind.

2 Soil Scientist, Western Soil and Water Management Research Branch, SWC, ARS, USDA, Manhattan, Kans.

Received for publication April 27, 1959. Accepted for publication July 31, 1959.






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