Tailings Improvement by Stress-Densification from Waste Rock Capping
Authors: Thomas E. Sully, Ken Brouwer, Peter K. Robertson, Graham Greenaway
Conference: Tailings and Mine Waste 2022
Date: November 6-9, 2022
ABSTRACT
Long-term risks associated with slurry tailings facilities are often related to the requirement for long-term containment of loose, saturated, and potentially fluid tailings. Saturated loose tailings have been known to liquefy with highly fluid mudflow events occurring after a tailings storage facility (TSF) breach, despite the absence of surface water ponding.
Risks associated with long-term tailings storage can be mitigated through the appropriate application of in-situ tailings improvement techniques, such as stress-densification, which can be a relatively economic ground improvement technology for low-density saturated tailings deposits. Stress-densification results when increased effective stresses cause consolidation of the tailings mass with an associated reduction in the moisture content, brittleness and potential mobility of liquefiable tailings.
Two 30 m high test pads were constructed by selectively placing waste rock on the surface of the decommissioned Candelaria TSF. The test pads were sized to replicate the loading that would be caused by construction of a thick, gently sloping waste rock closure cap, and evaluate tailings improvements relating to stress densification.
Site investigations were carried out before and after test pad construction to assess changes to the in-situ state and strength characteristics of the tailings. The field investigations were supplemented with specialized laboratory testing which quantified the effect of increasing confining pressure on the shape of the critical state line and demonstrated improvement in the undrained shear strength of the tailings.
The trial program demonstrates the efficacy of surcharge loading to stabilize and improve the residual shear strength characteristics of in-situ tailings. Improving the tailings shear strength properties can mitigate risks related to long-term tailings containment.
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