A pseudo 3D approach to predicting post-closure settlement in a tailings storage facility

Authors: Eadie, J; Bui, M; Greening, G Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_153

Cite As:
Eadie, J, Bui, M & Greening, G 2026, 'A pseudo 3D approach to predicting post-closure settlement in a tailings storage facility', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-13, https://doi.org/10.36487/ACG_repo/2615_153



Abstract:
A key design consideration for tailings storage facility (TSF) rehabilitation is long-term settlement and consolidation. Long-term settlement can alter surface gradients and disrupt post-closure drainage networks. The magnitude of settlement is impacted by a range of factors including age, depth and tailings rate of rise, water management during operations, and foundation drainage conditions. This paper presents a case study of a consolidation assessment for a TSF including the data used to undertake the assessment, methodology, outcomes and proposed monitoring to calibrate the model. The methodology comprised a staged approach, coupling one-dimensional (1D) consolidation modelling with geospatial analysis of tailings thickness to approximate 3-dimensional (3D) settlement behaviour. This cross-valley TSF was commissioned in around 2000 and has been incrementally raised since then. Several factors are expected to lead to differential settlement across the facility, including the range of tailings depths (from less than 1 m to 70 m), co-disposal of waste rock in tailings at depths up to 20 m, and the presence of a rockfill decant causeway. The range of tailings depths and varying age of tailings present a challenge when assessing the final landform for the facility following settlement. To quantify settlement, 1D consolidation columns (ranging from 20 m to 70 m) were initially modelled, capturing the rate of rise for the 26 years of operation, and the age of tailings through the modelled profile. Input parameters were derived from site-specific Rowe Cell laboratory testing, with the results benchmarked against literature values for gold tailings. Outputs from the model comprised estimated settlement depth as a function of time based on the range of tailings thickness across the facility. Geospatial analysis was then undertaken to spatially integrate consolidation outputs with the mapped tailings thickness and internal rockfill geometry to predict the settlement depths and generate a final surface representative of conditions post settlement. This case study reinforces that robust operational record-keeping and early consideration of long-term settlement in landform design are essential to achieving reliable, sustainable post-closure outcomes for TSFs. Long-term settlement and consolidation is a key consideration for the design, operation and closure of tailings storage facilities (TSFs) as it can alter surface gradients with potential consequences for drainage performance, erosion control and long-term stability of the closure landforms. The prediction of settlement and consolidation is important for informed planning and risk management as regulatory and stakeholder expectations are for no or low maintenance post-closure outcomes. Assessing settlement is complex due to the nature of tailings deposits. Settlement behaviour is influenced by factors such as tailings thickness, age and rate of rise, operational water management practices, material properties and foundation drainage conditions. These factors often have spatial and temporal variability, particularly in TSFs that have been constructed and raised incrementally over multiple decades. The presence of internal structures or co-disposed materials, such as waste rock or rockfill causeways, further increases the potential for differential settlement and non-uniform deformation of the tailings surface. The impacts of consolidation are often considered late in the life of the TSF, when closure designs are already constrained and operational records may not fully capture operational deposition. This highlights the value of operational record-keeping and early consideration of long-term settlement for TSFs with variable deposition strategies, tailings properties and tailings thickness. This paper presents a case study of a TSF commissioned around the year 2000 and progressively raised over approximately 26 years of operation. The TSF contains varying tailings thickness – from less than 1 m to approximately 70 m – and includes zones of waste rock co-disposed within the tailings and a rockfill decant causeway. The objective of this paper is to demonstrate a practical, pseudo 3-dimensional (3D) approach for evaluating long-term consolidation settlement across a TSF with significant variability in tailings thickness and material composition. The approach combines one-dimensional (1D) consolidation modelling with spatial mapping of tailings and internal rockfill structures to illustrate how settlement predictions can be integrated into spatial analyses to inform post-closure surface and drainage assessments. The outcomes of the case study provide insight into the importance of early and data-driven consideration of settlement processes in supporting reliable and sustainable TSF closure designs.

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