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Fan, Jiying
Geosynthetics , Geomembrane , Leakage , Tailings , Piping , Hole
Experiments are conducted to investigate the impact of fines content on the compressibility and permeability of the cyclone tailings, and to quantify leakage through a GMB hole overlain by saturated tailings. The effect of hole shapes, hole sizes, GMB thicknesses, tailings thicknesses, tailings homogeneity, applied stresses, water heads, subgrade grain-size distributions and surface irregularity, and a geotextile filtration layer on leakage and piping through the GMB defect are evaluated. It is shown that increasing the fines content from 0 to 100%, the involvement of the fine and coarse components of soil skeleton can be classified into four categories: no fines involvement, fines partially involved, increasing cushioning effect surrounding the coarse, and constant cushioning effect. For leakage through a circular GMB hole, a 1.9- and 5.0-fold increase in hole diameter cause a 1.8- and 6-fold increase in leakage, respectively, whereas a 2-fold increase in GMB thickness results in an 10% decrease in leakage. With the filter incompatible subgrade, a 2- to 4.5-fold higher leakage arising from piping is prone to occur at small consolidation stress or with a larger hole. The extent of tailings erosion into the subgrade depends on the filter compatibility and surface regularity of the subgrade, which could be significantly improved by increasing its fine particle component or placing a nonwoven needle-punched geotextile beneath the GMB. Changing the hole shape from circular to noncircular increases the leakage. There is no significant variation among leakage through triangular, diamond, and square holes, whereas the maximum increment is observed for the rectangular hole. With a constant rectangular length of 100 mm and increasing the rectangular width from 1.7 to 40 mm, the magnitude of leakage increment arising from the noncircular hole shape drops from 2-fold to 1.1-fold. The percent of head loss within the hole is independent of loading condition and only depends on the hole geometry (i.e., shape and size) and GMB thickness. A simple empirical equation predicting leakage through a circular GMB hole, considering the localized concentration of head loss around the hole and the consequent heterogeneity in hydraulic conductivity due to seepage force, is proposed and validated.
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