Numerical Aspects to Evaluate Triggering of Static Liquefaction with the HSS Model

Abstract

The assessment of tailings static liquefaction has become a key topic in recent years. Recent failures of upstream-raised tailings storage facilities (TSF) have raised concerns on the stability of these dams. The stability relies on the strength of tailings, which are loose and normally consolidated materials that may exhibit strain-softening during undrained loading. Standard practices to evaluate global stability of TSFs entail the use of limit equilibrium analyses, which consider peak or residual undrained shear strengths. These procedures do not consider the work input required to drive the softening process that leads to progressive failure. This paper describes the calibration and application of the Hardening soil model with small strains to evaluate the static liquefaction triggering of upstream-raised TSFs. A calibration methodology is proposed to capture the complete stress path of the softening behavior. Focus is given on the stiffness parameters that control both the rate of elastic and plastic volumetric strains. The parameters used for the non-linear solver and their numerical implications are discussed. A variety of trigger situations are considered. A real TSF is modelled in Plaxis 2D to evaluate its vulnerability to liquefy due to an undrained lateral spreading at the foundation. It is shown that this procedure is useful to verify the robustness of the TSF design.