Recent failures of upstream-raised tailings storage facilities (TSF) resulted in higher standards required by the mining industry on assessing the risk of tailings flow liquefaction.
Standard industry practice entails the use of limit equilibrium analyses to compute a factor of safety -or, in the best case, a probability of failure- assuming peak or residual undrained shear strength ratios; this procedure, however, fails to account for the effect of strain-softening and brittleness, as it neglects the work input required to drive the softening process that leads to a progressive failure.
This paper applies a numerical procedure to evaluate the flow liquefaction triggering of a real TSF; the methodology entails the use of finite element models employing the Hardening Soil model with small-strain stiffness, calibrated for this purpose by focusing on the stiffness parameters that control the evolution of shear-induced plastic volumetric strains; this calibration is able to effectively reproduce the stress-strain curve in undrained shearing, including the peak and residual undrained shear strength ratios and their associated deformations.
In the example shown, a TSF construction sequence is modelled in detail and subsequent trigger analyses are carried out for several scenarios, including: an undrained load at the dam crest, to represent a rapid embankment raise; and a contraction at the toe, to represent eventual movements due to creep or operational accidents.
Results show that this numerical modelling is useful to evaluate the flow liquefaction potential of the facility and to validate its robustness after the construction of a reinforcement buttress.
