Rainfall induced transient pressure wave mechanisms in tailing dams

The failure of tailings dams are most frequently attributed to liquefaction, erosion and overtopping. The purpose of this study is to investigate alternative physical/hydrological processes resulting from high rainfall intensities causing slope instability. In particular,
the advancing wetting front may cause transient air pressure waves to rapidly increase the phreatic surface and change pore water suction status. Some research has been conducted on this phenomenon in natural hillslopes but have not been considered in the case of tailings dams. In order to quantify these physical processes, specific experiments have been conducted. Laboratory work included a large leak-proof column filled up to 2.65 m with silica fines material with similar hydraulic characteristics as platinum tailings at in-situ dry bulk density. The column was instrumented with seven
data ports, each consisting of a time domain reflectometry probe to measure volumetric water content, a mini tensiometer to sense pore water pressure and a pore air pressure
probe. The experimental setup allowed for the application of artificial rainfall at different intensities and controlled boundary conditions, during automatic logging of the hydraulic state variables. Recorded observations showed that after the application of water to the soil surface, pore air pressure ahead of the wetting front increased rapidly,
causing air pressure wave propagation to mobilise pre-event water and reduce pore water suction. This led to the conclusion that high intensity rainfall events are likely to contribute to the generation of transient pressure waves in tailings porous medium, thereby inducing the rapid transmission of pressure head to a potential failure plane, where changes to effective stress may contribute to slope instability.