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This research was conducted to study the changes in the properties of a mixture consisting of a chemically treated bentonite and sand in contaminant environments. Seven chemicals and their aqueous solutions were used. The effects of chemicals on the soils were stressed by directly introducing the chemicals to the soil specimens and observing the changes in their properties over one year.
Index tests included expansion and sedimentation tests. These tests provided a good measure of soil-chemical compatibility. Permeability measurements were made using a consolidometer permeameter, a flexible wall permeameter, and a triple ring permeameter which was developed for this research. The triple ring permeameter preserves the advantages and compensates for the limitations of other types of permeameters.
At consolidation pressures most likely to prevail in a slurry wall, the coefficient of permeability increased with increasing concentration of the chemicals. If a soil showed less expansion in a given liquid, its permeability was observed to increase more. Tests with aniline, phenol, toluene, and 1,1,1-trichloroethane did not yield any significant adverse effect on the permeability. The largest increases were observed with sodium hydroxide. With the same chemical solutions the increases in permeability were considerably smaller at a confining pressure greater than 100 kPa.
A four-phase soil system is proposed which incorporates the effect of semi-solid expanded volume of the bentonite. Two parameters, er and ef, are defined which can account for the changes in the expansion of the bentonite resulting from the influence of chemicals. The coefficient of permeability decreases with increases in er and ef values.
permeability, expansion, permeameters, hazardous waste, contaminated permeants, bentonite, slurry wall
Senior geotechnical engineer, PSE&G, Newark, NJ
Professor, New Jersey Institute of Technology, Newark, NJ