The new understandings from collaborative research programs between Klohn Crippen Berger Ltd and the Geo-Engineering Centre at Queen’s University, Kingston, Ontario, provide a technical basis for quantifying leakage rates from tailings / geomembrane liner systems. The research program utilized hard rock copper tailings, which was screened to produce tailings with permeability in the range of 10-6 m/s to 10-9 m/s. Tailings were placed over a geomembrane, which had a hole varying from 1 mm to 10 mm in diameter, with a soil underliner of varying permeability. The samples were placed in a 590 mm diameter by 500 mm high rigid wall cell and subjected to a range of pressures up to 2000 kPa. A series of tests were out carried to assess the sensitivity of the leakage rate to: geomembrane type (LLDPE and HDPE); hole size; effect of wrinkles; effect of contact regularity; pressure; tailings permeability; underliner permeability; and, potential for piping.
The test results indicate that leakage from tailings / geomembrane liner systems is orders of magnitude less than leakage from typical landfill and heap leach geomembrane liner systems. The low leakage rate is due to the constraint of flow into a hole in the liner by the low permeability tailings. The rate of leakage is also non-linearly controlled by the permeability of the tailings and the head on the liner, but for many applications the leakage rate is on the order of 40 liters per day per hectare, assuming good quality control-quality assurance (QA-QC) and 10 mm diameter holes. The leakage rate reduced with the size of the hole, although with holes on the order of 1 mm, the leakage rate was not measurable.
Placement of tailings over wrinkles, which had a hole placed in the wrinkle, resulted in tailings infilling the folds of the liner and, therefore, limiting the effect leakage. Placement of pea gravel under the geomembrane resulted in piping of tailings through the hole indicating that control of the piping potential is required. Placement of a geotextile between the geomembrane and pea gravel controlled the piping. Further research is currently being carried out to understand the piping process, which currently suggests that although piping does occur, its extent may be limited by the reduction in flow through the hole and local “plugging” of the pea gravel.
Joshi, P. and McLeod, H. 2018. “Effectiveness of Geomembrane Liners in Minimizing Seepage in Tailings Storage Facilities: New Knowledge,” in Proceedings of the 26th International Congress on Large Dams, July 4-6, 2018. Vienna, Austria: International Commission on Large Dams.