A novel direct shear apparatus to evaluate internal shear strength of geosynthetic clay liners for mining applications
Date
2016
Authors
Soleimanian, Mohammad R., author
Bareither, Christopher A., advisor
Shackelford, Charles D., committee member
Schaeffer, Steven L., committee member
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Abstract
The use of geosynthetic clay liners (GCLs) in engineering practice has grown extensively over the past three decades due to application of this material containment applications such non-hazardous solid waste, residential and commercial wastewater management, roadways, and other civil engineering construction projects. This growth has been supported by an enhanced understanding of the engineering properties of GCL as well as hydraulic and mechanical behavior for different applications. In particular, the internal shear strength of GCLs is an important design consideration since GCLs often are installed on sloped surfaces that induced internal shear and normal stresses. The objective of this study was to develop a direct shear testing apparatus to measure the internal shear strength of GCLs for use in mining applications. The direct shear apparatus was designed to support the following testing conditions for needle-punched reinforced GCLs: hydration and testing in non-standard solutions (e.g., pH ≤ 1 or pH ≥ 12); testing under high normal stresses (up to 2000 kPa); and testing at elevated temperatures (up to 80 °C). Ultra-high molecular weight polyethylene GCL shear boxes were developed to facilitate testing 300-mm-square and 150-mm-square specimens under displacement-controlled conditions. Experiments were conducted on 150-mm-square and 300-mm-square GCL specimens to (i) evaluate gripping surface effectiveness as a function of peel strength and normal stress, (ii) assess hydration procedures to adopt into a systematic shear-testing protocol, (iii) assess stress-displacement behavior for 150-mm and 300-mm GCL shear tests, and (iv) develop failure envelopes for peak shear strength (τp) and large-displacement (τld). Shear behavior and peak and large-displacement shear strengths measured on both 150-mm and 300-mm square GCL specimens compared favorably to one another as well as to data from a previous study on a similar GCL. These comparisons validated the direct shear apparatus developed in this study and support the use of small GCL test specimens to measure internal shear behavior and shear strength of reinforced GCLs. Furthermore, the pyramid-tooth gripping plates developed to transfer shear stress from the interfaces between geotextiles of the GCL and shear platens to the internal region of a GCL were effective for a needle-punched GCL with peel strength of 2170 N/m and at normal stress ≥ 100 kPa.
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Subject
direct shear
geosynthetics
internal shear strength
geosynthetic clay liner
apparatus design
high temperature