Tailings dams have been in the spotlight over the last decade due to the number of failures and the severe consequences imposed on human life and the environment. In this context, the design of the tailings storage dams should examine critical lifetime scenarios likely to impact their stability. This PhD thesis investigates the performance of tailings sand dams in a highly seismic environment, by employing the coupled Hydro-Mechanical (HM) Finite Element (FM) modelling implemented in the Imperial College Finite Element Program (ICFEP) on the El Torito tailings dam as the principal case study. The first part of the thesis focuses on characterising the relevant tailings sand and calibrating a state parameter-based bounding surface plasticity model (BSPM). A challenging calibration process is performed for a range of densities and stress levels applicable to a tailings dam. The second part examines the impact of dynamic boundary conditions (BCs) applied in the numerical model and of the lateral model dimensions on the seismic response of a tailings dam. These were examined parametrically to select the most appropriate for the case study. The third part investigates the construction, operation and seismic responses of the El Torito tailings dam. The dam is analysed with a 2D plane strain FE model and HM coupled consolidation approach. The construction stage generates the static state conditions, while the seismic response is examined with the 2015 Illapel Earthquake, reproducing satisfactorily the available monitoring data and validating the numerical model. The seismic response of the model is then investigated under different scenarios of tailings properties and seismic events. For the scenarios examined, different aspects of the seismic response are evaluated (e.g. liquefaction in the impoundment), and the overall seismic stability of the dam is examined. Finally, the performance of a cost-effective centreline model is studied, contrasting with the static and seismic response of the El Torito dam. The case analysed shows that the dam’s stability is maintained, however, different deformation mechanisms are generated, producing local instabilities.