Numerical Analyses of Earthquake Induced Liquefaction and Deformation Behaviour of an Upstream Tailings Dam

Abstract

Much of the seismic activity of northern Sweden consists of micro-earthquakes occurring near postglacial faults. However, larger magnitude earthquakes do occur in Sweden, and earthquake statistics indicate that a magnitude 5 event is likely to occur once every century. This paper presents dynamic analyses of the effects of larger earthquakes on an upstream tailings dam at the Aitik copper mine in northern Sweden. The analyses were performed to evaluate the potential for liquefaction and to assess stability of the dam under two specific earthquakes: a commonly occurring magnitude 3.6 event and a more extreme earthquake of magnitude 5.8. The dynamic analyses were carried out with the finite element program PLAXIS using a recently implemented constitutive model called UBCSAND. The results indicate that the magnitude 5.8 earthquake would likely induce liquefaction in a limited zone located below the ground surface near the embankment dikes. It is interpreted that stability of the dam may not be affected due to the limited extent of the liquefied zone. Both types of earthquakes are predicted to induce tolerable magnitudes of displacements. The results of the postseismic slope stability analysis, performed for a state after a seismic event, suggest that the dam is stable during both the earthquakes.

Numerical Analysis of an Upstream Tailings Dam Subjected to Pond Filling Rates

“…The horizontal displacements were assumed to be zero along the lateral edges (i.e., both left and right vertical boundaries). These hydraulic and mechanical boundary conditions can be found in many previous works dealing with two-dimensional numerical simulations of upstream tailings dams [7,[11][12][13][14][15]. The finite element mesh of the upstream tailings dam after the last construction stage is shown in Figure 2.…”

“…Note that the actual consolidation in the facility is two-dimensional under the assumption of plane strain or axisymmetric conditions, at least at the straight portions of the tailings impoundments and dams [10]. With regard to the use of the advanced numerical approach for a tailings dam, there have been a number of studies addressing two-dimensional numerical simulations [7,[11][12][13][14][15]] and three-dimensional numerical simulations [16][17][18]. In the study by Psarropoulos and Tsompanakis [12], an investigation on the mechanical behavior and the stability of a tailings dam under static and dynamic loading was performed.…”

“…Their numerical model considered the consolidation processes under self-weight loads, continuous addition of water with the tailings discharge, infiltration of rainwater, and evaporation. Ormann et al [7,11] and Zardari et al [15] boused the two-dimensional finite element method for the simulations of both consolidation processes and the stability of an upstream tailings dam. Ormann et al [7,11] focused on static aspects, i.e., stability of a curved embankment and strengthening by rockfill embankments, whereas Zardari et al [15] focused on earthquake-induced liquefaction of an upstream tailings dam.…”

“…Ormann et al [7,11] and Zardari et al [15] boused the two-dimensional finite element method for the simulations of both consolidation processes and the stability of an upstream tailings dam. Ormann et al [7,11] focused on static aspects, i.e., stability of a curved embankment and strengthening by rockfill embankments, whereas Zardari et al [15] focused on earthquake-induced liquefaction of an upstream tailings dam. However, none of the abovementioned references have closely evaluated the effects of the pond filling rates on excess pore water pressure and the stability of an upstream tailings dam.…”

Response of a Lebanese Rock-Filled Dam to Seismic Excitation

“…In 2017, Auchar Zardari [9] investigated a dam response in Sweden by the FEM method for two earthquakes (the Skellefte'a earthquake and the Virginia earthquake). The Aitik tailings dam was modelled using two different behaviours: the Mohr-Coulomb and the UBCSAND model.…”