Piping of silty sand tailings through a circular geomembrane hole

Experiments are conducted to study leakage and piping through circular geomembrane holes from the overlying silty sand tailings. Three subgrades, a poorly graded gravel, a well-graded gravel, and a poorly graded sand are studied. Test results show that leakage through the geomembrane hole is not proportional to the surface area of the hole. A 5-fold increase in hole diameter from 10 to 50 mm results in an approximately 6-fold increase in leakage. With the filter incompatible subgrade, piping is prone to occur at small consolidation stress and/or with a larger hole. Open voids within soil skeleton induced by piping result in a 2-to 4.5-fold higher leakage than in the no-piping cases. The extent of silty sand piping and internal erosion 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 layer of nonwoven needle-punched geotextile beneath the geomembrane.