This paper addresses the earthquake response of a tailings dam with liquefiable sandy-gravel foundation. Geometry of the analyzed dam and the considered foundation conditions are typical for valley compacted earth and rockfill dams in the Andes of South America. Loose to medium dense saturated sandy-gravel foundation conditions can compromise stability of the tailings dam, especially in active seismic zones where large magnitude earthquakes may induce liquefaction of the saturated alluvial foundation material eventually culminating in flow failure beneath the downstream section of the dam.

Results of dynamic liquefaction analyses of the tailings dam – foundation system, considering alternatives for liquefaction mitigation (i.e., downstream buttress and/or in-situ foundation improvement) under two different seismic loading scenarios are presented and discussed. The effectiveness of the analyzed liquefaction mitigation measures is evaluated in terms of earthquake-induced deformations of the existing starter dam and of the proposed ultimate dam configuration.

The dynamic liquefaction analyses were conducted using a non-linear two-dimensional finite-difference scheme along with a fully coupled effective stress constitutive model. The selected geotechnical parameters and input earthquake time records as well as constitutive model calibration to laboratory test results are discussed in the paper. Results from the idealized case study analyses of both buttress and foundation improvement alternatives showed that the foundation improvement is the most effective to mitigate the liquefaction hazard for the ultimate dam configuration subject to earthquake loading.

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