Dynamic effective stress analysis of a centreline tailings dam under subduction earthquakes

A case study was conducted to evaluate the seismic performance of a centreline tailings dam in the South American Andes through dynamic effective stress analyses with advanced constitutive models. The seismic demand at the dam site was evaluated through a probabilistic seismic hazard assessment (PSHA), from which deterministic and probabilistic-based seismic design criteria were derived. The PSHA results were used to select spectrally matched ground motions for the subsequent dynamic analyses. The plan is for the centreline tailings dam to be raised in stages to a height of 90 m; this was considered in establishing the initial stresses and pore pressures before seismic loading. The material properties were based on a large geotechnical characterisation programme considering the mine tailings to be stored in the deposit and other critical dam components. Dynamic analyses were performed using the UBCHYST constitutive model for materials that are not expected to generate significant excess pore pressures and the PM4Silt constitutive model for materials that may generate excess pore pressures due to cyclic loading. The results showed the deformation patterns in the centreline dam, after seismic loading, to be significantly affected by the presence of mine tailings. The results of this work will be useful in planning the overall operational management of the tailings facility.