Leakage through Holes in Geomembranes below Saturated Tailings

Experiments conducted to quantify potential leakage from holes in two geomembranes [1-mm-thick linear low-density polyethylene (LLDPE) and 2-mm-thick high-density polyethylene (HDPE)] placed on a silty-sand [underliner hydraulic conductivity ($k_{\mathrm{UL}}$), $1.1\times {10}^{-7}\le k_{\mathrm{UL}}\le 1.2\times {10}^{-5}\mathrm{m}/\mathrm{s}$], or pea gravel ($k_{\mathrm{UL}}=1\times {10}^{-2}\mathrm{m}/\mathrm{s}$) underliner (foundation/subgrade) and covered with saturated fine tailings at 65% initial solids content are discussed [tailings hydraulic conductivity ($k_T$), $2.9\times {10}^{-8}\le k_T\le 1.6\times {10}^{\mathrm{-6}}\mathrm{m}/\mathrm{s}$]. Tests results show that the overlying tailings, with a $k_T<k_{\mathrm{UL}}$, filled the geomembrane hole and had a larger effect on flow through the hole than the underliners examined. For the tested conditions, leakage through 10 and 20-mm-diameter holes were essentially the same whereas the leakage through a 1.5-mm-diameter hole was three orders of magnitude lower. Introduction of a $580\mathrm{g}/{\mathrm{m}}^2$ nonwoven needle-punched geotextile (GTX) layer between the geomembrane and tailings increased the flow by approximately 60%. A gap below geomembrane hole attributable to a stone on the underliner filled with tailings, which flowed through the hole. The evidence of fines migration through the hole, from the tailings to the underliner is discussed.