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As a consequence of hazardous and toxic waste disposal in the subsurface environment, triaxial permeability and strength tests on contaminated soils or with hazardous pore fluids must be conducted for extended time periods. The determination of hydraulic conductivity and shear strength of contaminated soils (or of uncontaminated soils using contaminated permeants) requires equipment and procedures different from those required for conventional triaxial permeability and strength testing.
The application of a back pressure works well to maintain saturation for short-term testing but may be insufficient for long-term testing. Procedure and equipment modifications are required to maintain saturation. Reservoir modifications may be made to dissolve contaminants at the solubility limit. Frequent replacement of influent permeant may maintain saturation and influent equilibrium. Equipment modifications may be required due to the chemical nature of the permeant and its incompatibility with the equipment. Long-term testing variables also include gradient, effective stress, particle migration, differential consolidation, diffusion through the membrane, and changes in water chemistry. Due to the need to permeate the specimen with at least one pore volume of permeant, gradients higher than those typically encountered in the field are used. This results in high effective stresses and differential consolidation. The volatile nature of certain permeants may cause diffusion through the membrane and changes in influent chemistry throughout the test.
laboratory testing, hydraulic conductivity, hazardous waste, soil mechanics, geotechnology, clays, triaxial, permeameters, compatibility
Associate professor, Bucknell University, Lewisburg, PA
Professor and director, Lehigh University, Bethlehem, PA