Ghazi Zadeh, Shahin, authorBareither, Christopher A., advisorShackelford, Charles D., committee memberScalia, Joseph, committee memberBailey, Travis, committee member2019-09-102019-09-102019https://hdl.handle.net/10217/197371The objective of this study was to evaluate the shear behavior of a composite system consisting of geosynthetic clay liner (GCL) and textured geomembrane (GMX) in mining applications. In current practice, design of liner and cover systems for waste containment is based on results of displacement-controlled internal and interface shear tests, which commonly include GCL and GMX specimens hydrated in de-ionized or tap water and tested at room temperature (e.g., 20 °C). However, the use of GCL/GMX composite systems in liner and/or cover systems for mine waste containment (e.g., heap leach pads, tailings impoundments, waste rock piles) may be exposed to physical and environmental stresses that are not conventionally replicated in laboratory testing, such as high shear and normal stresses, elevated temperature, and/or non-standard solutions. Laboratory testing conducted under conventional experimental conditions may not represent appropriate stresses anticipated in field conditions. To address the aforementioned concerns and aid the design of liner and cover systems for mining applications, four main objectives were defined: (i) assess variability of internal reinforcement fibers and shear strength in GCLs; (ii) evaluate the effect of GCL and GMX characteristics on shear behavior of GCL/GMX composite systems; (iii) evaluate temperature effects on the shear behavior of GCL/GMX composite systems; and (iv) evaluation the effects of non-standard solutions on GCL internal and GCL/GMX interface shear strength. These objectives were addressed via laboratory experiments, which included approximately 400 direct shear tests, 150 peel strength tests, and 50 swell index tests. Comparable internal shear behavior was observed between 300 mm x 300 mm GCL specimens and 150 mm x 150 mm GCL specimens. Similar variability in peak internal shear strength was also observed in both size GCL specimens. Variation was also observed in GCL peel strength among specimens obtained from the same production roll. Variability in internal shear strength and peel strength were attributed to the spatial variability of reinforcement fiber characteristics within a given GCL roll. The failure mode of a GCL/GMX composite system in an interface direct shear test was a function of shearing normal stress and characteristics of the GCLs and GMXs. An increase in spike density of a GMX increased the critical strength of GCL/GMX composites at all normal stress. However, an increase in GCL peel strength most effectively increased critical strength of a GCL/GMX composite at high normal stresses when GCL internal failure occurred. Internal and interface direct shear testing at an elevated temperature to 80 °C resulted in reductions of both GCL internal and GCL/GMX interface shear strength. The reduction in GCL internal shear strength was due to a reduction in tensile strength of reinforcement fibers and reduction in the strength of the connection between reinforcement fibers and geotextile of the GCL. The reduction in GCL/GMX interface shear strength was attributed to a reduction in the interlocking strength between GMX spikes and fibers of the geotextile of the GCL, as well as a reduction in geotextile-GMX interface friction. Hydration of GCL and GMX specimens up to 10 months in synthetic acidic and alkaline mining process solutions did not produce noteworthy change in GCL internal shear strength, GCL-GMX interface shear strength, or GCL peel strength. However, stiffer shear behavior was observed in internal and interface shear tests on GCL and GMX specimens hydrated with the synthetic acidic mine process solution. Hydration with the synthetic acidic mine process solution reduced swell behavior of sodium bentonite, whereas no conclusions were made regarding the effect of hydration with alkaline mine process solution on bentonite swell behavior.born digitaldoctoral dissertationsengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text