Graduation Year

2004

Document Type

Thesis

Degree

M.S.C.E.

Degree Granting Department

Civil Engineering

Major Professor

Ashmawy, Alaa

Keywords

barriers, liners, swell index, engineered clay, permeability

Abstract

Bentonite clay is widely used in barrier systems due to its low hydraulic conductivity and it high swell capacity. Exposure to inorganic solutions can cause significant increases in hydraulic conductivity, due to changes in the surface chemistry and fabric. This phenomenon can be attributed to a reduction in the thickness of the double layer, due to the cation exchange capacity of the clay. The clay can be modified with polymers to render it less susceptible to chemical attack. The treatment process allows the clay to be engineered to enhance specific properties, such as permeability and sorption. In the present study, engineered soils are prepared by sorbing organic polymers to the surface of Na-bentonite. Three classes, cationic, anionic and nonionic polymers are investigated. The sorbents are water-soluble compounds based on the polymerization of acrylamides (PAM). Mixing and sample preparation techniques are developed and discussed.

The interaction of the polymeric compounds and the clay mineral surface are evaluated by testing the liquid limit, swell index and specific gravity of the soils. Permeability tests are performed to determine if the polymer treatment enhances the hydraulic performance of the clay when permeated with highly concentrated salt solutions. The effect of permeant, void ratio, initial wetting condition and preparation techniques are found to have a significant affect on the hydraulic conductivity.

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