Modelling unsaturated silty tailings and the conditions required for static liquefaction

Abstract

The potential for static liquefaction of tailings is a major focus in the design and operation of tailings storage facilities. This research models the behaviour of unsaturated tailings, with a variety of degrees of saturation, addressing the propensity for static liquefaction during monotonic loading. Unsaturated triaxial tests, including constant suction conditions and constant water-air mass conditions, were performed. A bounding surface plasticity model was used to simulate the results. The constant mass condition is relevant to undrained closed-system loading, which may prevail during fast-deformation after the tailings becomes unstable, when the air and water in the pore space remain locked inside the tailings. Boyle's law and hydraulic hysteresis were accounted for to model the changes of pore air and water pressures, and suction, with the tailings volume change. Good agreements were achieved between test results and model simulations. Additional simulations which mimic rising water tables under constant total stress states in the field, situations which may trigger instabilities, are also shown. Results are added to charts which relate peak and post-liquefaction strengths, and collapse lines, to measures of initial state, for unsaturated conditions, which may be of use in practice.

Constitutive modelling of instabilities and strengths of an unsaturated tailings

“…For unsaturated conditions approximations have been made, specifically omitting the work done by the air-water interface, e.g. Buscarnera and his colleges [3] for the water undrained case and Wang et al for the closed system case [4]. The instability points identified by these two approaches are extremely close to being identical.…”