Centrifuge and Numerical Modeling of Liquefied Flow and Nonliquefied Slide Failures of Tailings Dams

Tailings dams have relatively high failure rates throughout the world and the consequences of these failures often result in significant loss of life and damage to the environment and property. However, the triggers and failure mechanisms are typically hypothesized and not well understood. To investigate potential triggers and the corresponding failure mechanisms, two centrifuge model tests were conducted on loose slopes made of gold tailings using a scaled viscous fluid to induce instability in flight. A numerical back-analysis was also carried out to investigate and verify the associated mechanisms. Two failure mechanisms were observed in the centrifuge tests. In the first test, large seepage forces caused sloughing at the toe. The initially drained instability at the toe induced significant positive excess pore pressures due to the loose state, as well as to the initially higher degree of saturation in the toe region, triggering localized liquefaction at the toe (undrained response). Due to the localized liquefaction, the tailings at the toe could not support the tailings upstream of the toe, triggering a retrogressive flowslide failure. In the second test, a slope failure occurred due to drained instability, i.e., failure occurred once the drained factor of safety approached unity. No liquefaction was evident, due to the initially lower degree of saturation in the toe region, as well as to the slower rate of shearing compared to the first test. As revealed by both physical and numerical simulations, the structural collapse of the soil resulted in the drained instability of the slope, which triggered a slide-to-flow failure.