Physical Performance of Geomembranes Used in Heap Leach Pad Applications

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Irfan, Huma
Heap Leach Pads , Geomembranes
Geomembranes (GMB) are normally used as part of the liner system in heap leach pads. There is a need to quantify tensile strains in the geomembrane that could affect short-term puncture and long-term performance of the GMB. In this thesis, short-term tensile strains arising from indentations caused from the material placed both below and above the geomembrane are quantified, and the potential for puncturing is investigated. Experiments were conducted on 1.5 mm high-density (HDPE) and liner low density polyethylene (LLDPE) geomembranes for applied pressures up to 3000 kPa. The geomembrane punctured from underliner material having gravel and sand placed directly beneath the geomembrane and a peak tensile strain of 40% was induced. Increasing the sand fraction to obtain a well graded gravel and sand underliner resulted in peak tensile strains of 14% in the geomembrane and caused no puncture. When geomembrane is underlain by geosynthetic clay liner (GCL) and compacted clay liner, the tensile strains increased with increasing deformability (due to higher water content) of the underlying material. Experiments were also conducted to examine the implications of overliner material and pressure on geomembrane strains. It was found that the overliner having gravel and some sand resulted in 18% tensile strain in the geomembrane at 2000 kPa and 27% for 3000 kPa. A gravelly sand overliner with some silt induced tensile strains of 9% and 12% at 2000 kPa and 3000 kPa respectively. None of the overliners was able to limit stains in the geomembrane to less the maximum recommended geomembrane strain proposed in the literature. A 150-mm-thick silty sand layer placed above coarsest overliner examined reduced the geomembrane strains to 2%, even when subjected to pressures of 3000 kPa.
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