Abstract
Standard practice to evaluate global stability of Tailings Storage Facilities (TSFs) entails the use of limit equilibrium analyses, which considers either peak or residual undrained shear strength of the saturated area and drained shear strength for the unsaturated soils and tailings. This practice might still be non-conservative, as nearly saturated materials can develop excess pore pressures and behave in an undrained mode. Moreover, limit equilibrium analyses does not account for the work input required to drive the stress state past the peak and into the softening process.
Numerical deformation models, on the other hand, can readily model the transition from saturated to unsaturated conditions and from peak to residual strength, and therefore are able to provide further insight of the static liquefaction vulnerability of a given dam.
This paper describes the application of finite element modelling in Plaxis 2D to the analysis of the vulnerability of a TSF to static liquefaction. The procedure employs off-the-shelf features like the Hardening Soil Model with Small Strain Stiffness (HSS) constitutive model and Van Genuchten Soil Water Characteristic Curve (SWCC) to simulate the shear-induced generation of pore pressure in the saturated and nearly saturated materials while providing a smooth and physics-friendly transition from the fully undrained to the fully drained behaviours of the various portions of the dam.
It is demonstrated that, by providing a step-like SWCC, the procedure produces nearly identical results to those obtained by ignoring suction altogether and zoning the dam by hand. This, by itself, is useful, because the position of the phreatic surface can be varied within the model without the need of remeshing. On the other hand, if a realistic SWCC is employed, the vulnerability of the facility can be better understood and reported.
