Tailings storage facilities are critical mine structures that must perform safely under changing operational and environmental conditions. International guidelines and best practice emphasize robust monitoring and clearly defined operational controls to ensure adverse trends are detected early and managed. Trigger Action Response Plans are central to this approach, linking observed behaviour to predefined trigger levels and response actions. Upstream‑raised facilities present challenges, including complex deformation patterns that do not necessarily correspond to conventional failure modes. When post‑construction deformations exceed initial expectations, operators must distinguish between mechanisms such as long‑term volume change and creep of rockfill and mechanisms that could evolve into instability and then reflect this understanding in their TARPs.
This paper presents the discussion of the post-construction behaviour of a downstream buttressed TSF, based on an assessment of instrumentation data taken from a monitoring system that includes vibrating wire piezometers, shape array inclinometers, survey prisms, ground‑based radar, and a real‑time data dashboard. Monitoring results show displacements greater than those assumed in design, with movements largest at lower elevations of the buttress and smaller at the dam crest. Deformation rates accelerate after major rainfall events, coinciding with rapid pore pressure responses in shallow piezometers, while deeper piezometers and bedrock instruments show slower responses. As part of the phenomenon, a system of longitudinal cracks that developed along the crest and berms was assessed.
To interpret this behaviour, a conceptual geotechnical model and a suite of kinematic hypotheses were developed. Mechanisms involving large‑scale block sliding or tailings‑driven instability are inconsistent with the combined deformation and pore pressure evidence. The most likely mechanism is a rainfall-induced densification of the buttress rockfill, particularly in its thicker lower zones. The resulting conceptual model is used to guide refinement of monitoring and the review of trigger levels and response actions, illustrating how integrated monitoring and kinematic reasoning can support risk‑informed operational control of a deforming TSF.
