A weak water risk management approach and ensuing low strength or brittle behaviour affect the general risk of a tailings dam facility. This can impact your insurance premiums and your internal risk management programme costs. Globally, most tailings dam failures when investigated showed poor surface water management and related low strength tailings.
Water in the tailings should be managed actively whether the dam is using solar drying alone or in combination with mechanical compaction. The tailings dam should be designed in a manner that ensures maximum exposure to the sun. Effective water risk management helps avoid low strength brittle tailings from being formed. It reduces the risk of overtopping or dam wall failure due to slope instability.
Tailings behaviour is generally classified as ductile (good) or brittle (ill-behaved). On ductile tailings, the strength and behaviour can support upstream or centreline construction approaches. If a tailings dam failure occurs on a ductile tailing, it often results in a gradual downslope movement which can be minimised in terms of damage by reinforcing with rockfill or similar materials. Brittle tailings usually are associated with loose, saturated sand/silt-sized tailings which can have sudden collapses with rapid movement and large outflows. Brittle tailings can also occur where tailings are dumped in a loose state and further deposits are made on this loose state. Depositing a layer of loose tailings within a compacted stack, or re-saturation of a layer may compromise the strength of the layer.
Good water risk management lowers the risk associated with the dam and generally results in lower insurance premiums (if externally insured) or lower fund reserves (if self-insured). As a risk management best practice, the tailings dam is not supposed to be used for holding excessive water. Depending on the size of the operation, the mine can consider having an offline dam primarily for process water with a spillway or a water treatment plant. Also, the decant and pond as a guide should be 3 times the final tailings dam height from the perimeter wall in upstream raise or centreline constructions to avoid compromising the perimeter walls.
Some of the information considered when assessing tailings dams water risk for insurance purposes include:
In conclusion, there is a lower risk of a Tailings Dam failure where there is minimal water stored on top. In the event of an embankment failure, the damage from outflow from a well-operated dam is restricted. At Firstlink, we advise mining clients on overall Tailings Dam risk management matters that enable them to manage their risks effectively and where insured, obtain economic terms.
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