Document Type

Thesis

Date of Award

1-31-1990

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Raj P. Khera

Second Advisor

Jay N. Meegoda

Abstract

Soil-Bentonite Walls offer a cost effective solution to many groundwater problems in new and remedial work projects such as hydraulic barriers in dams, dewatering large soil cuts, and as part of pollution control systems around hazardous waste landfills. However, the performance of soil-bentonite walls in environments other then fresh water types is still a matter of great controversy. In recent years, some data on soil-bentonite backfill have became available. The data indicate change in properties of these walls with time of exposure and concentration of chemicals found in leachates. However, no research work is available in the literature on the desiccation effect on the integrity of soil-bentonite walls.

A series of experiments was conducted to study the effects of dry-wet cycles on the backfill materials composed of bentonite and other soil components. To simulate field conditions, one half of a specimen was subject to cycles of drying and wetting while the other half was maintained dry. Solutions of aniline, phenol and hydrochloric acid were used as the liquids. Soil-bentonite backfill containing 10 percent bentonite showed the most cracking. The size, number, and the density of the cracks increased along the dry-wet interface and spread in the other areas as the number of drywet cycles increased. The largest cracks were formed with phenol solution and the smallest cracks with water. Samples subjected to hydrochloric acid solution showed no cracks, but did exhibit some dissolution. When clay contents of the backfill mix were increased the size and density of the cracks decreased.

All the cracks essentially Closed when the specimen was subjected to permeability tests due to effective confining pressure. Permeability tests on the cracked specimen did show change in permeability of an order of magnitude or slightly greater.

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