The recently published Global Industry Standard on Tailings Management (GISTM) requirements do not make specific reference to geotechnical investigation requirements for basin and embankment foundation assessment of tailings dams. The Tailings Management Good Practice Guide does, however, emphasise the primacy of site characterisation, and its importance and contribution to the entire life cycle of the facility from its inception to its closure. This has been highlighted, particularly in some of the tailings storage facility (TSF) failures in recent times such as the Mount Polley and Cadia failures, in which embankment wall foundation failures could be ascribed to ground conditions that were, in hindsight, not adequately identified or characterised during the initial investigation phase.
This paper aims to provide an overview as to what may need to be considered and investigated to provide an adequate site characterisation regarding, particularly, the ground conditions to meet the aims of the GISTM. The conventional approach would likely be to prescribe certain data point densities, and depths of investigation based on the eventual size of the TSF, and associated infrastructure (e.g. return water dams, slit traps, slurry delivery systems, penstock towers, etc). However, the authors wish to present an alternative approach where the level of investigation activity and intensity is dictated by the complexity of the whole geological setting. The aim of the investigation should be to define the engineering geological ground model of the site, to inform the method of dam construction to be considered, and the risks to be mitigated in its construction, operation, and final closure.
The role of the engineering geologist in greenfield TSF developments is twofold. The first requirement is to develop an engineering geological ground model of the area to satisfy the design team that the three-dimensional structure of all potentially weak zones in foundation, basin, and adjacent areas that may induce or impact on failure, have been identified and geotechnically characterised. The second requirement is to support project cost and environmental sustainability objectives by identifying, characterising, and determining the lateral and vertical extent of potential construction material resources in the basin area. To fulfill these objectives, multiple site investigation phases may be required, depending on the sequential development of the TSF as well as the complexity of the site geology, and geomorphology of the site. A newly constructed hillside facility will require extensive storm water diversion infrastructure to accommodate increasing climate change-induced flood events, which a paddocked facility on flat topography will not necessarily require.
