Report on the Immediate Causes of the Failure of the Fundão Dam

The Fundão tailings dam failed on November 5, 2015 in a liquefaction flowslide that initiated at the dam’s left abutment. This Investigation was performed to determine its cause.

In structuring its investigation process, the Panel systematically identified and evaluated multiple causation hypotheses. It further imposed hypothesis testing by means of the following three questions that the candidate failure mechanism should be able to explain: (1) Why did a flowslide occur? (2) Why did the flowslide occur where it did? (3) Why did the flowslide occur when it did?

The Fundão Tailings Dam Review Panel was constituted by Cleary Gottlieb Steen & Hamilton LLP, which was retained jointly by Samarco Mineração S.A. and its shareholders, BHP Billiton Brasil Ltda. and Vale S.A., to conduct an investigation to determine the immediate cause of the November 5, 2015 Fundão tailings dam failure. Panel members: Norbert Morgenstern, Professor Emeritus of Civil Engineering at the University of Alberta; Steven G. Vick, engineering consultant; Bryan D. Watts, Chairman of Klohn Crippen Berger Ltd.; and Cássio Viotti, engineering consultant. The aspects of the investigation related to seismicity were conducted by Gail Atkinson, Professor of Seismology at the University of Western Ontario; and Ivan Wong, Principal Seismologist for Lettis Consultants International, Inc.