Erosion of silty sand tailings through a geomembrane defect under filter incompatible conditions

At tailings storage facilities, a geomembrane may be used to contain tailings from relatively more permeable foundation or embankment materials. A "filter incompatible" condition may arise between the tailings and underliner materials. In this study, the potential for piping erosion of tailings through a 1cm diameter geomembrane defect was evaluated in a series of physical experiments. The geomembrane defect was sandwiched between silty sand tailings and various underliners (DF15/DB85 = 5.6-13.5) not meeting typical retention criteria for filtration. The leakage rates and visual findings revealed that a critical stress condition existed where erosion occurred continuously for up to 24 h. This stress condition could be encountered during early deposition or development of a reclaim pond at a tailings storage facility. When allowed to occur, erosion during this stress condition resulted in subsequent leakage rates that were 2-3 orders of magnitude higher than previously observed with "filter compatible" conditions and higher stresses. Practitioners unaware of this potential for erosion near the defect may significantly underestimate leakage and underpredict pore pressures within the embankment.