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Results of a laboratory study of the effects of acidic and caustic permeants upon the permeability of various fine-grained soils are reported. Triaxial falling head permeability tests were performed on specimens of kaolinite, kaolinite-bentonite mixture, and magnesium montmorillonite. Permeants used were hydrochloric acid with pH values of 1, 3, and 5 and water and sodium hydroxide with pH values of 9, 11, and 13. In no case for any of the clays or permeant pH did the permeability increase during the passage of six pore volumes of permeant, which indicates that no significant dissolution of clay minerals occurred. The only permeant that caused significant change in permeability was sodium hydroxide at a pH of 13, which caused a reduction in permeability of the magnesium montmorillonite by a factor of 13. This was found to be due to precipitation of magnesium hydroxide in the pores. Results are compared with findings reported by other researchers.
It is concluded that because of the wide variety of reactions possible between clays and permeant, future reports of permeability changes should give as much detail as possible about the chemistry and mineralogy of the soil studied. The equipment used and testing technique also have significant effects on reported test results and should be described in detail. Also, it is suggested that research is needed into possible reactions which could be induced within the soil pores to create favorable changes in permeability.
permeability, permeameters laboratory testing, hazardous waste, contaminated permeant, clay soils, earth linings, soils testing, triaxial devices
Assistant professor, University of Missouri—Rolla, Rolla, MO
Assistant engineer, Anderson Engineering, Inc., Springfield, MO
Associate professor, University of New Haven, West Haven, CT