Date of Award

Spring 1989

Document Type

Dissertation

Degree Name

Doctor of Engineering Science in Civil Engineering

Department

Civil and Environmental Engineering

First Advisor

Raj P. Khera

Second Advisor

Su Ling Cheng

Third Advisor

Paul C. Chan

Fourth Advisor

Jay N. Meegoda

Fifth Advisor

Manish Chandra Bhattacharjee

Abstract

This research was conducted to study the characteristics of permeability and volume change of bentonite-sand mixes due to contaminants. The soil specimens consisted of clean sand, bentonite, and fly ash. Test liquids included seven diluted organic and inorganic chemicals and a landfill leachate.

Index tests included liquid limit, expansion, cracking, and sedimentation tests. Expansion tests proved to be the most useful for permeability evaluation in a contaminant environment.

The conventional consolidometer permeameter and flexible wall permeameter proved to be not completely satisfactory for testing soft bentonite mixes. A triple ring permeameter was developed to compensate for the limitations of these equipment and to provide a more convenient means of testing.

The test results indicated that diluted chemicals showed an adverse effect on permeability. However, when the consolidation pressure increased and the void ratio decreased, this effect tends to be minimized. Consolidation pressure also restricted the adverse effect of cracking in a specimen and caused no permeability increase. The change of permeability generally agrees with the results found in the index tests and can be explained by the Gouy-Chapman theory.

The fly ash from one local source mixed with bentonite did not help to reduce the permeability. The expansion of the bentonite appears to be limited in the mixtures due to the effect of ion replacements.

Permeability tests conducted on bentonite-sand mixes indicated that void ratio could not be correlated well with permeability due to the effect of expanded volume of the bentonite. A four-phase soil diagram with two physical parameters, expansion ratio, er, and expansion function, ef, is proposed. It can clearly express the volumetric changes of bentonite in a mix resulting from the influence of the chemical. Permeability was found to be strongly correlated to these parameters. It decreased with an increase in er and ef. The concept of expansion appears to be very helpful in evaluating the permeability response of a bentonite mixture in a contaminant environment.

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