Seismic Induced Flow Failures of Mine Tailings Including a Failure Case History from Chile

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The 2010 M8.8 Maule Chile earthquake caused damage over a large area of the country. Of particular interest was the flow failure of a gold mine tailings dam in the central region of Chile. A 25m high tailings dam experienced liquefaction due to strong ground shaking and flowed downslope as far as 350m resulting in several fatalities as well as degradation of the surrounding area. When tailings material liquefies it often behaves like a non-Newtonian fluid, requiring threshold shear stress before exhibiting strain rate dependent shear strength. The transition from liquefaction triggering to steady state flow, to runout involves interesting and complex physics that will be discussed. Predicting the stability of tailings dams subjected to earthquake shaking requires an estimate of the residual strength of the liquefied material. Post-earthquake field investigations of the Chile failure established the in situ engineering properties (SPT, CPT, VS) of the tailings material, and the liquefied residual strength for the failure was derived through the back calculation. The results augment the existing worldwide database to be used for future predictive models that help prevent similar failures in the future.

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Robb Moss, PhD., P.E., F.ASCE is a professor of Geotechnical, Earthquake, and Risk Engineering at Cal Ploy in San Luis Obispo, CA. His research focuses on seismic liquefaction engineering, surface fault rupture, cyclic failure of sensitive clays, seismic site response, seismic soil structure interaction, flow failures/debris flows, and the application of probability and risk concepts to those engineering hazards. He has several years of consulting experience as a geotechnical earthquake engineer in the US and abroad. He has been part of the nine NSF-funded earthquake reconnaissance teams investigating failures in: Mexico, Japan, Turkey, Chile, India, Nepal, California and Alaska. Currently he is a Fulbright Specialist to Chile focusing on the topic of Engineering Education. He is also part owner and founding member of a subsurface investigation company in Chile. Robb grew up in Montana and is happy to be back here for 6 months on sabbatical.