Estimation of Seismic Load for Design of Low Consequence Category Tailings Dams

Seismic design of embankment dams often requires assessment of the earthquake induced ground and dam movements. There are multiple cases where earthquakes have resulted in sliding and lateral spreading of embankments, crest settlement, and in some instances liquefaction and embankment failure. Hence, evaluation of the effects of earthquakes on embankment dams is of paramount importance for the design. A site-specific seismic hazard study is generally the first step to estimate the potential earthquake loads and the results are often presented in the form of site response spectra, earthquake time histories, and/or plots of peak ground acceleration (PGA) for “rock outcrop”. The PGA and earthquake motions which are used in liquefaction, stability and deformation analyses of embankment dams are to be further processed to develop those within or at the top of the structure. Empirical ratios or deconvolution of the input motion are used for this purpose. There are significant uncertainties involved with the former approach whilst for the deconvolution process earthquake time histories are vital, which are not readily available, at least during the early stages of a project. In this study, a series of one-dimensional response analyses of several Australian dam sites were carried out using SHAKE software (GeoMotions, 2012) to investigate the effects of material parameters (i.e. shear wave velocity) and embankment height on amplification ratios. The results are presented and compared in this paper. A general framework is also provided to estimate the PGA for the embankment analyses for low to significant consequence category tailings dams in Australia where the earthquake design load or a site-specific seismic hazard analysis is not available.