Effect of embankment construction quality on stability of Aketao tailings dam under rainfall-seismic coupling

The heightening treatment of tailings dams may lead to catastrophic dam failure accidents. The Aketao tailings dam, with a height of 22 m, has been in operation for 14 years. Increasing dam height was considered to meet new demands on tailing management. The influence of added drainage layers and improved relative density of on slope stability was analyzed through a series of field survey, laboratory tests, numerical simulation under heavy rainfall and earthquakes. The research results showed that when the dam height is increased from 22 m to 85 m, accompanied by added drainage layers and improved relative density of the tailings, the factor of safety for slope stability increased significantly. The burial depth of the infiltration line increased with added drainage layers and approached a stable value for excess of 3 layers. Similar results were obtained for increased relative density of the tailings, where relative density of 0.7 was determined optimum minimum value for marked improvement. Furthermore, the finite element model simulations showed marked decrease in magnitude and spread of liquefied zones on the dam surface with the added drainage layers and densification of the tailings. The reduction in occurrence of liquefied zones was attributed to the significant drop in excess pore water pressures inside the dam body. Similarly, marked decrease in the magnitude of maximum horizontal and vertical deformations due to earthquake loading was predicted, where the location of the maximum deformation appeared to shift from the dam surface to the interior of the dam. From both safety and economic perspective, it is recommended that the relative density of the tailings embankment be no less than 0.7, and that 3 horizontal drainage layers be arranged at equal lifts along the heightened portion of the dam. The research results provide theoretical basis for safe heightening of similar tailings dam.