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Water Content and Bulk Density During Wetting of a Bentonite-Silt Column¹

ABSTRACT

An improved method of dual-energy gamma-ray attenuation was used to measure water content and bulk density rapidly and accurately, during one-dimensional, unsaturated water movement into a column of an equal-part mixture of initially air-dry, highly swelling bentonite and silt. The bulk density near the inlet end of the column decreased rapidly as water entered. Since the ends of the column were confined, the expansion of the wetted bentonite-silt produced a compensating compression in the remaining air-dry portion of the column. Several water-content variables were plotted against the so-called reduced material coordinate m/t^1/2 (Boltzmann variable expressed in terms of the material coordinate m and time t). Neither the volumetric water content nor the volumetric water ratio would coalesce the data when plotted against m/t^1/2. In contrast, a plot of water saturation vs. m/t^1/2 did coalesce the data into a single curve, except for very early times at positions nearer than 1 cm to the water inlet.

¹ Journal Paper no. 5998, Purdue Univ. Agric, Exp. Stn., West Lafayette, IN 47907. Contribution from the Dep. of Agronomy, Partial support was from funds provided by the U.S. Dep. of the Interior, Office of Water Res. and Tech., as authorized under the Water Resources Research Act of 1964. Presented before Div. S-1 (Soil Physics), Soil Sci. Soc. Am., 31 Oct. 1972, at Miami Beach, Florida.

² Graduate Research Assistant and Professor of Soils, respectively; first author is now Assistant Professor of Agronomy, Oklahoma State Univ., Stillwater, OK 74074.

Received for publication September 3, 1975. Accepted for publication January 30, 1976.