Intraplate seismicity is characterized by few, dispersed, and irregularly occurring earthquakes. The modelling technique presented in this paper is not unique for the Aitik tailings dam and can be used for other tailings dam facilities. The above information on seismicity in Sweden suggests that it is important to analyse liquefaction potential and stability of the Aitik dam by taking into account both normal and extreme seismic conditions in Sweden. In this study, numerical modelling of seismic liquefaction of the Aitik tailings dam is performed with the finite element program PLAXIS 2D, using a recently implemented advanced constitutive model called UBCSAND (see ). More case studies of this type are needed in order to gain more experience of numerical modelling of seismic liquefaction in tailings dams. Some similar case studies regarding seismic behaviour of geotechnical structures (mainly embankment dams) could be found in the literature (see, e.g., ). To the authors’ knowledge, there are just a few case studies of tailings dams published, where such advanced numerical tools have been used (see, e.g., ). Therefore, it is appropriate to investigate seismic behaviour of the tailings dam with advanced numerical software, based on, for example, the finite element method. Seismic liquefaction in a tailings dam is a complex phenomenon.
It is relevant to mention here that several tailings dams, located in different parts of the world, have failed due to seismic liquefaction (see, e.g., ). The deformations progressively increase with each cycle of loading and may lead to failure of the dam. In the liquefied state, large deformations could occur due to low stiffness of the tailings. If the excess pore pressures increase to such an extent that effective stresses are reduced to near zero, it could lead to liquefaction (see, e.g., ). As a result, excess pore pressures increase cumulatively with each cycle of loading. In this type of dam structure, pore water in saturated tailings may not drain as rapidly as seismic shaking occurs. In this raising method, dikes are sequentially constructed on the previously deposited tailings that could be in a loose and saturated state. The Aitik tailings dam is mainly raised using the upstream construction method. In such a long time perspective, it is therefore relevant to consider the possibility of a large magnitude earthquake. Guidelines on tailings dams in Sweden suggest that a tailings dam needs to be stable for at least 1000 years. Using the available database of earthquakes that have occurred in Sweden since the 19th century, there are indications of approximately one magnitude 5 event every century and one magnitude 6 event every millennium. In Sweden, approximately one earthquake with magnitude above three occurs every year. The purpose of this study is to evaluate liquefaction potential, permanent deformations, and the stability of the dam under both a commonly occurring Swedish earthquake and a more extreme event. It is one of the first attempts to investigate the stability of a tailings dam in Sweden, using numerical methods to study dynamic loading. This paper presents finite element analyses of dynamic behaviour of the Aitik tailings dam in northern Sweden in response to the impact of an earthquake. 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. Both types of earthquakes are predicted to induce tolerable magnitudes of displacements. It is interpreted that stability of the dam may not be affected due to the limited extent of the liquefied zone. 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. The dynamic analyses were carried out with the finite element program PLAXIS using a recently implemented constitutive model called UBCSAND.
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. This paper presents dynamic analyses of the effects of larger earthquakes on an upstream tailings dam at the Aitik copper mine in northern Sweden. However, larger magnitude earthquakes do occur in Sweden, and earthquake statistics indicate that a magnitude 5 event is likely to occur once every century. Much of the seismic activity of northern Sweden consists of micro-earthquakes occurring near postglacial faults.
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