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Movement of Air through Water in Partly Saturated Soils


WHEN the water content of a soil is reduced below saturation, the interfaces between air and water lie within pores, and are curved because of surface tension, σ. The pressure of the water Pw is lower than that of the surrounding air Pa by where rs is the radius of the interfaces. As the water content is reduced, drainage occurs from progressively smaller openings, and the interface radius decreases. The pressure of the water also falls, in accordance with equation 1, producing the well known “suction‐moisture content” relationship.

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WILLIAMS, P. Movement of Air through Water in Partly Saturated Soils. Nature 212, 1463–1464 (1966).

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