Date of Graduation

12-2017

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Richard Coffman

Committee Member

Michelle Bernhardt-Barry

Second Committee Member

Findlay Edwards

Keywords

Compacted Clay Liners, Hydraulic Conductivity, In-situ Testing, Landfills, Soil Water Characteristic Curves, Two Stage Borehole

Abstract

The methods utilized to determine the hydraulic conductivity of compacted clay liners (CCLs) are of importance for safe guarding the environment from landfill leachate. Therefore, the methods utilized in the analysis of the Two Stage Borehole (TSB) test, as described in the ASTM D6391-11 (Method A, B, and C) standard, were evaluated. Data from hydraulic conductivity tests, as performed on three test pads, were utilized to review the ASTM D6391-11 equations. Additionally, two test pads were instrumented with volumetric water content and soil water matric potential sensors to facilitate the determination of field-obtained soil water characteristic curves (SWCCs) and hydraulic conductivity functions (k-functions) for unsaturated soils. For the determination of the SWCCs and k-functions, each test pad was subjected to an infiltration cycle, using either a sealed double ring infiltrometer or a two-stage borehole infiltrometer, followed by a drying cycle. To compare the results that were obtained from the field-obtained SWCCs and k-functions, laboratory tests were performed on Shelby tube samples acquired from the corresponding test pad. The obtained data were fitted using the van Genuchten model and the RETC (RETention Curve) program.

The results that were obtained from TSB testing led to the conclusion that Method B and C, as written in the ASTMs D6391-11 standard contained errors that impacted the results that were obtained from hydraulic conductivity testing. Specifically, utilizing Method C provided results that were four times greater than the hydraulic conductivity and utilizing Method B provided results that were as much as two orders of magnitude greater than the hydraulic conductivity. Several recommendations are proposed herein to ensure accurate hydraulic conductivity analysis is performed in the future. It was further determined that a poor agreement exists between field-obtained and laboratory-obtained k-functions and SWCCs, as reported in other studies. Therefore, field-obtained k-functions are preferential, when available.

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