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A Mechanism by which Organic Liquids Increase the Hydraulic Conductivity of Compacted Clay Materials¹

ABSTRACT

The ability of concentrated organic chemicals, with low dielectric constants (E) to increase the hydraulic conductivity of compacted soils has been well documented. This study was undertaken to evaluate a mechanism by which these increases occur. Theory predicts that the spacing between adjacent clay particles diminishes as the E value decreases. Hydraulic conductivity measurements were made in fixed wall permeameters with a range of concentration of organic liquids in water. Marked increases in hydraulic conductivity occurred at concentrations above which the clay flocculated. Smectite d spacings increased when the clay was equilibrated with acetone and ethanol solutions having E values ranging from 65 to 77, but decreased when equilibrated with solutions having E values <35 to 50 as compared to that in water. All three clays tested exhibited reductions in electrophoretic mobility (µ) and the absolute value of the zeta potential|| which would be associated with flocculation at low E values. Relative clay content measurements indicated that all three soils flocculated in solutions with low E values. At E values >49, all clays remained dispersed. When bulk samples were exposed to organic liquids, the volume changes were proportional to the E values of the permeant. The results indicate that when organic liquids or salts are sufficiently concentrated, soil particles will be drawn closer together until the clays flocculate. Thus, changes in the surface electrical properties of the clays cause shrinkage, resulting in cracking and increases in hydraulic conductivity. Flocculation tests and E values may be used as tools to predict the influence of a solution on the hydraulic conductivity of compacted soils.

¹ Contribution of the Texas Agric. Exp. Stn., Texas A&M Univ., College Station, TX. This work was funded by EPA Cooperative Agreement CR-808824-030.

² Professor and Research Associate, respectively, Soil and Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843.

Received for publication September 15, 1986.