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    Elevated Temperature Effects on Geotextile-Geomembrane Interface Shear Behavior
    (Asce-Amer Soc Civil Engineers, 2021) Karademir, Tanay; Frost, J. David
    The performance of geosynthetic layered systems during their service life in terms of interface shear behavior and strength properties is of major importance in certain geotechnical applications. The interfaces between geotextiles and geomembranes in landfill applications are subject to temperature changes. In this respect, interface shear behavior requires assessment of the engineering strength properties of the components, both independently and collectively, at different temperatures. To this end, an extensive research study was undertaken to investigate temperature effects on the interface shear behavior between needle-punched nonwoven (NPNW) polypropylene (PP) geotextiles and both smooth polyvinylchloride (PVC), as well as smooth and textured high-density polyethylene (HDPE) geomembranes. A temperature-controlled chamber (TCC) was utilized to simulate the field conditions at elevated temperatures and evaluate shear displacement and frictional response mobilized at different temperatures. The physical laboratory testing program consisted of interface shear tests between material combinations found in landfill applications under a range of normal stress levels from 10 to 400 kPa and at a range of ambient temperatures from 21 degrees C to 50 degrees C. An increase in temperature from the standard laboratory test temperature of 21 degrees C to an equivalent in situ temperature of 50 degrees C increases the peak and postpeak interface friction values by a minimum of 14%. For selected combinations of materials, the amount of increase can be in excess of 20% and as high as 22%. Consequently, interface shear behavior determined at room temperature yields interface friction values that are conservative at higher temperatures.
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    Micro-scale tensile properties of single geotextile polypropylene filaments at elevated temperatures
    (Elsevier Sci Ltd, 2014) Karademir, Tanay; Frost, J. David
    Geotextiles are porous and fibrous materials that consist of randomly oriented and isotropically distributed long filaments which vary in terms of spatial distribution, curvature, orientation, size, and mass density. The heterogeneous internal structure of geotextiles constituted from individual/discrete fibers and having different micro-structure and macro-structure properties are prone to exhibit dissimilar tensile stress-strain behavior (i.e. progressive versus reactionary) as well as showing favorable versus adverse response to varied experimental conditions such as temperature and strain rate change when tested at macro scale as opposed to micro-scale level. To this end, in order to evaluate thermo-tensile strength properties as well as to characterize tensile extension behavior of single geotextile filaments at micro-scale level, micro-mechanical tensile tests were performed at different temperatures using a Dynamic Thermo-Mechanical Analyzer (DMA) on single filaments extracted from polypropylene needle punched nonwoven geotextile. Various test temperatures between 21 degrees C and 50 degrees C were chosen to represent and simulate the wide range of temperatures encountered in the field for geotechnical applications such as landfill base liners. The paper also presents a statistical analysis of the results of the test program to provide a basis for comparison of inherent filament variability. (C) 2014 Elsevier Ltd. All rights reserved.