Seepage through TSFs is commonly assumed to occur under gravity flow and is usually determined only under steady-state conditions. However, seepage is also highly influenced by the degree of saturation of the materials involved in these structures and can influence the stability of TSFs. TSFs in areas of alternating dry and wet seasons present additional challenges for the evaluation of soil-asmospheric interations.
The objective of this research was a comprehensive review of the parameters that influence the phreatic surface within the TSF under steady-state conditions and to assess how this behaviour changes under transient conditions. The soil-water characteristic curve (SWCC) and shrinkage curve were analysed to determine their responses to transient conditions.
For the numerical modelling stage, a generic upstream TSF was analysed with a finite element model to determine the location of the phreatic surface under steady-state conditions. Then, a transient seepage analysis was employed to assess the most influential parameters on the TSF stability considering an extremely rainy season. In the model, the effect of the hydraulic boundary conditions of the drain, the beach length, the hydraulic anisotropy of tailings, the segregation of the beach and the influence of the hysteresis of the SWCC were considered as part of assessing the stability of the upstream dam.
The results suggest that the most influential parameter on dam stability is the pond’s position on the impoundment, indicating a relationship between the height of the TSF and the beach length. The efficiency and sound design of the drainage system are also essential to prevent the phreatic surface from rising to the top of the dam and are key to increasing the factor of safety. On the other hand, tailings anisotropy, beach segregation and the SWCC hysteresis only have a secondary role, and their impact on the factor of safety is minimal.
