The Relationship Between Plasticity Ratio and Hydraulic Conductivity for Bentonite Clay During Exposure to Synthetic Landfill Leachate

Author

Whitney M. Allen, University of South Florida

Graduation Year

2005

Document Type

Thesis

Degree

M.S.C.E.

Degree Granting Department

Civil Engineering

Major Professor

Alaa Ashmawy, Ph.D.

Co-Major Professor

Jeffrey Cunningham, Ph.D.

Committee Member

Manjriker Gunaratne, Ph.D.

Keywords

Atterberg limits, permeability, landfill liners, index properties, chemical compatibility

Abstract

In landfill design, the containment of solid and liquid contaminant is essential. Leachate is produced from the biodegradation of the waste with the migration of liquid including rain-water through the heap. This liquid can become a health hazard if it leaches into the groundwater. Liners are placed beneath leachate collection systems to prevent leachate from seeping into the soil underneath the landfill.

Compacted clay liners, usually containing bentonite clay, are widely used. Bentonite can be characterized by its low hydraulic conductivity and high swell potential. With a low hydraulic conductivity, the liner can serve as a barrier. The high swell potential aids in the integrity of a liner when suffering from cracking or puncturing.

The chemicals that can be found in leachate are capable of increasing the clays hydraulic conductivity due to chemical interactions. Chemical compatibility testing - laboratory hydraulic conductivity tests using specific chemical solutions as a permeant - are performed to determine the effects. Laboratory hydraulic conductivity tests, regardless of the permeant, can be time-consuming and expensive.

In this study, pure Wyoming bentonite clay and Bentofix clay were used. Deionized water and 0.01M, 0.1M, 0.5M concentrations of four inorganic salt (NaCl, KCl, MgCl₂, and CaCl₂) solutions were the liquids to which both clays were exposed during testing. Plastic limit and liquid limit tests were run on both clays with all 13 liquids. Laboratory hydraulic conductivity testing with pure Wyoming benonite clay was done with 12 different permeants- all solutions except 0.01M CaCl₂ and 0.5M CaCl₂. The hydraulic conductivity testing on Bentofix clay was run with 3 permeants- de-ionized water, 0.1M CaCl₂, and 0.1M NaCl.

The purpose of this study was to determine if a correlation exists between the experimentally determined liquid limit and plastic limit of a specific clay and its hydraulic conductivity when exposed to a synthetic leachate.

It was determined that a trend exists that will allow for less expensive and time-consuming determination for hydraulic conductivity of a clay liner when exposed to a specific chemical solution. However, more experimental data need to be collected before a definite trend is verified. The proposed procedure requires that a hydraulic conductivity test of the clay be run using deionized water as the permeant, and plasticity index tests be performed using the leachate.

Scholar Commons Citation

Allen, Whitney M., "The Relationship Between Plasticity Ratio and Hydraulic Conductivity for Bentonite Clay During Exposure to Synthetic Landfill Leachate" (2005). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/2772